The bearded airway

Anaesthesia, 1999, 54, pages 492–514 ................................................................................................................................................................................................................................................

Correspondence Awake insertion of the cuffed oropharyngeal airway for nasotracheal intubation

The cuffed oropharyngeal airway (COPA) (Mallinckrodt, Athlone, Ireland) has been used as an aid to both orotracheal and nasotracheal intubation, but in all cases the airway was inserted after the patient had already been anaesthetised [1–4]. We report a case of awake insertion of the cuffed airway and subsequent fibrescope-aided nasotracheal intubation in a patient with a difficult airway. A 25-year-old man with burns of the face and neck was scheduled for skin grafting to the face. His face and neck were disfigured due to burn contracture, and fashioning of a muscle flap and tissue expander in the neck (Fig. 1). Head and neck movements were restricted; the gap between incisor teeth at the maximum mouth opening was 1.5 cm. The patient consented for insertion of an object into his mouth, but not in the nose, before induction of general anaesthesia, because of previous experiences during attempts at nasotracheal intubation. After the patient had been sedated by propofol and fentanyl and the oropharynx topically anaesthetised using 8% lignocaine spray, the cuffed airway was inserted with minimal discomfort to the patient. Anaesthesia was induced with increasing concentrations of sevoflurane up to 5% in oxygen. The trachea was then intubated nasally using a fibrescope while the patient was breathing spontaneously through the cuffed airway. Throughout the procedure, oxygen saturation remained greater

than 98%. After correct tracheal intubation had been confirmed, the cuffed airway was removed and vecuronium injected. The operation proceeded uneventfully. Postoperatively, the patient did not recall any event during induction of anaesthesia.

tracheal tube into the trachea (Fig. 3). By connecting the breathing system to the cuffed airway, oxygen and inhalational anaesthetics can be delivered during attempts at fibrescope-aided nasotracheal intubation. We believe that in patients in whom both tracheal

Figure 1 Nasotracheal intubation was performed while the patient was breathing

adequately through the cuffed oropharyngeal airway. Note the deformity of the lower part of the face and neck due to burn contracture, muscle flap to the jaw, and tissue expander in the neck. Both mouth opening and head and neck movements were restricted.

The laryngeal mask is a useful aid to orotracheal intubation [5], but it may not be suitable for nasotracheal intubation, since the mask encloses the larynx (Fig. 2). In contrast, when the cuffed oropharyngeal airway is used, it is possible to advance the fibrescope and a

intubation and ventilation through a facemask are predicted to be difficult but awake tracheal intubation is inappropriate or unacceptable to the patient, awake insertion of the cuffed oropharyngeal airway and subsequent nasotracheal intubation after induction of anaesthesia

All correspondence should be addressed to Professor M. Harmer, Editor of Anaesthesia, Department of Anaesthetics and Intensive Care Medicine, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, UK. Letters (two copies) must be typewritten on one side of the paper only and double spaced with wide margins. Copy should be prepared in the usual style and format of the Correspondence section. Authors must follow the advice about references and other matters contained in the Notice to Contributors to Anaesthesia printed at the back of each issue. The degree and diplomas of each author must be given in a covering letter personally signed by all the authors. Correspondence presented in any other style or format may be the subject of considerable delay and may be returned to the author for revision. If the letter comments on a published article in Anaesthesia, please send three copies; otherwise two copies of your letter will suffice.

492

䊚 1999 Blackwell Science Ltd

Anaesthesia, 1999, 54, pages 492–514 Correspondence ................................................................................................................................................................................................................................................

oropharyngeal airway and Aintree intubation catheter. British Journal of Anaesthesia 1998; 80: 549P–50P. 3 Hawkins M, O’Sullivan E, Charters P. Use of a cuffed oropharyngeal airway to assist fibreoptic laryngoscopy and tracheal intubation using the Portex bougie. British Journal of Anaesthesia 1998; 80 (Suppl. I): 20–1. 4 Pigott DW, Kay NH, Greenberg RS. The cuffed oropharyngeal airway as an aid to fibreoptic intubation. Anaesthesia 1998; 53: 480–3. 5 Koga K, Asai T, Latto IP, Vaughan RS. Effect of size of a tracheal tube and the efficacy of the use of the laryngeal mask for fibrescope-aided tracheal intubation. Anaesthesia 1997; 52: 131–5.

Anaesthesia for thyroplasty

Figures 2 and 3 Nasotracheal intubation while either the laryngeal mask airway (Fig. 2)

or the cuffed oropharyngeal airway (Fig. 3) is in place. The laryngeal mask obstructs the passage of the fibrescope and tracheal tube to the trachea, rendering it difficult to intubate through the nose. In contrast, the presence of the cuffed airway allows insertion of the fibrescope and tracheal tube while oxygen and inhalational anaesthetics are provided through the cuffed airway.

(while maintaining spontaneous breathing) is a useful option. T. Asai H. Matsumoto K. Shingu Kansai Medical University, 570-8507, Osaka, Japan 䊚 1999 Blackwell Science Ltd

References 1 Uezono S, Goto T, Nakata Y, lchinose F, Niimi Y, Morita S. The cuffed oropharyngeal airway, a novel adjunct to the management of the airways. Anesthesiology 1998; 88: 1677–9. 2 Hawkins M, O’Sullivan E, Charters P. Fibreoptic intubation using the cuffed

May I thank Drs Griffin et al. (Anaesthesia 1998; 53: 1202–4) for their informative case report on anaesthesia for thyroplasty. We have used another technique on several occasions with satisfactory results and without taking up almost an entire operating session (i.e. 80 80 5 induction time 180 min). Anaesthesia is induced with propofol by target-controlled infusion using the Vial Fresenius pump and analgesia by continuous infusion of remifentanil at 0.05 mg.kgÿ1.minÿ1 following an initial bolus of 0.5 mg.kgÿ1; this is adjusted if respiration is less than 6 breath.minÿ1. Patients are allowed to breath with a target concentration of propofol of 4.5–5.5 mg.mlÿ1 and a respiratory rate of 8–12 breath.minÿ1. Oxygenation is maintained with the aid of oxygen via a nasal cannula at 4 l.minÿ1 and the airway is maintained using a direct laryngoscope with a microscope and camera attachment to view the vocal cords. Dexamethasone is also administered to reduce postoperative swelling and stridor. The entire procedure takes less than 1.5 h and the patients are woken at the end. Following a course of speech therapy, only one patient has felt it necessary to have a repeat procedure to have a larger prosthesis inserted. This repeat procedure was completed in less than 493

Correspondence Anaesthesia, 1999, 54, pages 492–514 ................................................................................................................................................................................................................................................

the original time as the window in the thyroid cartilage was still patent. Further speech therapy ensured that the patient had a stronger and deeper voice and could cough better. Following a haematoma development in one patient due to the direct laryngoscope, we have modified the technique as Griffin et al. suggests using an LMA and nasendoscope. Nevertheless, we feel that our patients would prefer not to be woken in the middle of surgery and given sedation. Furthermore, propofol infusions are not without their problems. I have some concerns over fixed infusion regimens using potent sedatives/hypnotics as they do not equilibrate immediately and it can take several minutes for the effect site to reach equilibrium with blood levels. Patients would almost certainly prefer a single method of anaesthesia. A. George Leighton Hospital, Crewe CW1 4QJ, UK

A reply We wish to thank Dr George for his informative letter regarding an alternative anaesthetic technique for this procedure. However, we would like to point out that the duration of the procedure did not have anything to do with the anaesthesia technique! Their point regarding haematoma development is well taken and we continue to use the LMA/nasendoscope for that reason. Similarly, we take their point regarding fixed infusion regimens – the propofol infusion we used was titrated to clinical effect during the voice analysis period. Our patient had a satisfactory result following speech therapy and did not require further surgery. M. Griffin F. Chambers Yale School of Medicine, CT 06520-8051, USA Percutaneous tracheostomy

We read with interest the survey report ‘Use and safety of percutaneous tracheostomy in intensive care’ (Anaesthesia 1998; 53: 1209–27). We would like to comment on some aspects of practice

494

in percutaneous tracheostomy, as borne out in the survey. We agree with the author that percutaneous tracheostomy is a well-established technique in intensive care. The reasons for this are its simple bedside application, ease of scheduling, avoidance of transporting critically ill patients requiring invasive monitoring, and its cost-effectiveness. Of the four known methods of percutaneous tracheostomy (PCT), only two are currently used widely [1]: the percutaneous dilatation technique described by Ciaglia (PDT) and the guidewire dilatation forceps technique (GWDF). The ‘Toye’ method and the ‘Rapitrac’ method have mostly fallen into disuse because of high complication rates [2–5]. Dr Cooper’s survey also shows that the Ciaglia method is in much greater use in the UK ICUs than is the GWDF method (72% vs. 43% of the survey respondents). Although there are no data available directly comparing the two methods, the literature indicates that the GWDF method is a much safer, quicker and more cost-effective method. Pooled data from over 1600 patients who underwent percutaneous tracheostomy shows that the overall peri-operative complication rate for the GWDF method is 1.2% compared with 7.6% for the Ciaglia method. The longterm postoperative complication rate reported is 2% for the GWDF method, and 5.5% for the Ciaglia method [1]. Serious complications, although uncommon, have been reported with the Ciaglia method (PDT) – false passage, pneumothorax, difficulty with dilatation, bronchospasm and death [6, 7]. There is no mortality reported with the GWDF method [8–10]. In our ICU, we performed 17 percutaneous tracheostomies in 1998. All of them were done using the GWDF (Portex kit) technique. A minor complication was encountered in only one patient – skin edge bleeding. Our very low complication rate may in part be due to proper patient selection, and previous experience with the standard open surgical tracheostomy technique. By sterilising and reusing the guidewire dilating forceps, the cost of the method is decreased. The dilators in the Ciaglia method are for single use only.

The mean (SD) operative time reported for performing PCT by the Ciaglia method is 15 (8) min [11]. The operative time reported for the GWDF method is 1–10 min [9]. The duration for percutaneous tracheostomy by GWDF method in our own ICU is 4–7 min. We consider that endoscopic guidance via the pre-operatively established airway is not necessary when using the GWDF technique because of: 1 visualisation of the trachea with the guidewire dilating forceps as a separate step, before introduction of the tracheostomy cannula, 2 ease of the procedure and 3 extremely low complication rate. On the other hand, endoscopic guidance seems to be desirable with the Ciaglia technique [12]. Based on current literature and our own experience, the GWDF method of performing percutaneous tracheostomy seems to be safer, quicker and more costeffective than the Ciaglia method. The rationale for development of alternative methods of tracheostomy has been the number and frequency of complications associated with the standard open method [1]. The complications associated with Ciaglia’s method are similar to those associated with the standard open technique [1], defeating one of the main reasons for developing alternative techniques. Further studies are needed to compare directly the Ciaglia method and the GWDF method for percutaneous tracheostomy. We are surprised that 2% of the survey respondents still use the Rapitrac method, considering that a 22.9% complication rate has been reported with this technique [1]. R. J. Morais S. Kotsev Dubai Hospital, Dubai, UAE References 1 Powell DM, Price PD, Forrest LA. Review of percutaneous tracheostomy. Laryngoscope 1998; 108: 170–7. 2 Toye FJ, Weinstein JD. Clinical experience with percutaneous tracheostomy and cricothyroidotomy



3

4

5

6

7

8

9

10

11

12

in 100 patients. Journal of Trauma 1986; 26: 1034–40. Pelousa EO. Percutaneous tracheostomy – ready or not. Journal of Otolaryngology 1991; 20: 88–92. Hutchinson RC, Mitchell RD. Life threatening complications from percutaneous tracheostomy. Critical Care Medicine 1991; 19: 118–20. Leinhardt DJ, Mughal M, Bowles B, Glew R, Kishen R, MacBeath J, Irving M. Appraisal of percutaneous tracheostomy. British Journal of Surgery 1992; 79: 255–8. Wang ME, Berke GS, Ward PH, Calcaterra TC, Watts D. Early experience with percutaneous tracheostomy. Laryngoscope 1992; 102: 157–62. Bobo M, McKenna SJ. The current status of percutaneous dilatational tracheostomy: an alternative to open tracheostomy. Journal of Oral and Maxillofacial Surgery 1998; 56: 681–5. Griggs WM, Worthley LI, Gilligan JE, Thomas PD, Myburg JA. A simple percutaneous tracheostomy technique. Surgical Gynaecology and Obstetrics 1990; 170: 543–5. Griggs WM, Myburgh JA, Worthley LI. A prospective comparison of percutaneous tracheostomy with standard surgical tracheostomy. Intensive Care Medicine 1991; 17: 261–3. Caldicott LD, Oldroyd GJ, Bodenham AR. An evaluation of a new percutaneous tracheostomy kit. Anaesthesia 1995; 50: 49–51. Hill BB, Zweng TN, Maley RH, Charash WE, Toursarkissian B, Kearney PA. Percutaneous dilatational tracheostomy: a report of 356 cases. Journal of Trauma 1996; 41: 238–43. Berrouschot J, Oeken J, Steiniger L, Schneider D. Perioperative complications of percutaneous dilatational tracheostomy. Laryngoscope 1997; 107: 1538–44.

Post pneumonectomy respiratory failure

In general, anaesthetists resort to highfrequency jet ventilation (HFJV) only


after failed conventional ventilation. However, consideration should be given to the use of HFJV via a minitracheostomy tube as a first-line measure in the post pneumonectomy patient who requires ventilatory support. Acute respiratory failure can complicate the postoperative course of pneumonectomy. Possible causes include: residual lung tissue inadequate for gas exchange, sputum retention, atelectasis, infection and pulmonary oedema. Patients who remain hypoxaemic, despite 100% oxygen and mask CPAP, often require mechanical ventilatory support. Conventional ventilation (highvolume low-rate) has a number of disadvantages, particularly in the post pneumonectomy patient. Tracheal intubation requires deep sedation, leaving the patient unable actively to clear secretions. High peak airway pressures may result in barotrauma to the single lung, and expose the bronchial stump to the risk of rupture. It is not surprising therefore that conventional ventilation following pneumonectomy is associated with a mortality rate of over 75% [1]. In our centre, the high mortality associated with conventional ventilation in this condition has led to a reluctance to institute it. Instead, we use HFJV via a minitracheostomy tube (Portex minitrach II) to provide mechanical respiratory support in the first instance. HFJV has been successfully used via a tracheal tube for routine postoperative ventilation, and via both tracheal tube and tracheostomy to aid weaning from conventional ventilation [2, 3]. There are a number of perceived advantages of HFJV over conventional ventilation. The peak inspiratory pressure required to achieve comparable oxygenation is reduced, there is a reduction in the air leak through any bronchopleural fistula and there may be less adverse haemodynamic effects, with improved urine output [4–6]. A lower peak airway pressure will reduce the risk of barotrauma and stump blow-out, which is especially relevant in the post pneumonectomy patient. HFJV delivered via a minitracheostomy was described by Matthews and colleagues, who claimed a number of advantages of this route [7]. There is good patient tolerance, and

minimal sedation is required. Spontaneous respiration is preserved. The minitracheostomy provides a port from which secretions may be aspirated, while glottic function is preserved, enabling the patient to assist in the clearance of secretions by generating an expulsive cough. Potential complications of the technique include bleeding from the minitracheostomy insertion site, and tube malposition or displacement [8], with the potential for gross tissue emphysema. However, given the length of a standard minitracheostomy tube, displacement should be a rare event. We have seen rapid improvement in oxygenation and clinical condition in a number of post pneumonectomy patients following the institution of HFJV via a minitracheostomy tube. However, this is not always the case, and some patients do ultimately require conventional ventilatory support. It may be that HFJV is only effective in those patients with a less severe condition and who may not ultimately have needed any form of mechanical support. The efficacy of HFJV via a minitracheostomy in this condition could only be accurately defined by the conduct of a randomised prospective trial. J. Wang S. M. Winship S. H. Pennefather G. N. Russell The Cardiothoracic Centre, Liverpool L14 3PE, UK References 1 Hirschler-Schulte CJ, Hylkema BS, Meyer RW. Mechanical ventilation in acute postoperative respiratory failure after surgery for bronchial carcinoma. Thorax 1985; 40: 387–90. 2 Sladen A, Guntupalli K, Marquez J, Klain M. High frequency jet ventilation in the postoperative period: a review of 100 patients. Critical Care Medicine 1984; 12: 782–7. 3 Klain M, Kalla R, Sladen A, Guntupalli K. High frequency jet ventilation in weaning the ventilator dependent patient. Critical Care Medicine 1984; 12: 780–1. 4 Sladen A, Guntupalli K, Klain M. High frequency jet ventilation versus

495


5

6

7

8

intermittent positive pressure ventilation. Critical Care Medicine 1984; 12: 788–90. Schuster DP, Klain M, Snyder JV. Comparison of high frequency jet ventilation to conventional ventilation during severe acute respiratory failure in humans. Critical Care Medicine 1982; 10: 625–30. Carlon GC, Howland WS, Ray C, Miodownik S, Griffin JP, Groeger JS. High frequency jet ventilation: a prospective randomised evaluation. Chest 1983; 84: 551–8. Mattews HR, Fischer BJ, Smith BE, Hopkinson RB. Minitracheostomy: a new delivery system for jet ventilation. Journal of Thoracic Cardiovascular Surgery 1986; 92: 673–5. Wain JC, Wilson DJ, Mathisen DJ. Clinical experience with minitracheostomy. Annals of Thoracic Surgery 1990; 49: 881–6.

A grading system for direct laryngoscopy

Drs Yentis and Lee’s recent paper is a welcome contribution to a discussion of the grading system for direct laryngoscopy (Anaesthesia 1998; 53: 1041–4). They evaluated a modification of the system devised by Cormack and Lehane [1] and subdivided grade 2 into easy (2a) and harder (2b) views. However, I do not believe the paper goes far enough. During attempted tracheal intubation, ease of laryngoscopy is an important ‘process variable’ but is not the only determinant of ease of intubation (the desired ‘outcome’). Consequently, reported definitions of difficult intubation vary widely and include (a) Grade 3 and 4 laryngoscopy, (b) the need to use specialist equipment, (c) more than two attempts at laryngoscopy, (d) more than three attempts at laryngoscopy, (e) intubation time more than 10 min, (f) failure to intubate the trachea. Only the first definition includes the laryngoscopic grade. Yentis and Lee used the definition ‘requiring more than one laryngoscopy, a specialist blade or other intubation aid such as the gum elastic bougie’. These could be regarded as rather ‘soft’ criteria.

496

Table 1

Laryngeal view

‘Old’ grade

Method of intubation

Modified grade

New grading

Most of cords Posterior part of cords Arytenoids only Epiglottis liftable Epiglottis adherent or only tip visible No laryngeal structures seen

1 2 2 3

Direct Direct Bougie Bougie

1 2 2b 3

EASY EASY RESTRICTED RESTRICTED

3 4

Specialist Specialist

3b 4

DIFFICULT DIFFICULT

It is recognised that the frequency of airway difficulty varies according to the definition used [2]. Classification of laryngeal view should stratify views associated with increasing degrees of intubation difficulty. This is inevitably difficult as increasing difficulty occurs in a continuous manner rather than stepwise. The point at which the grade changes should correspond with a clear increase in difficulty or alternatively with a change in practical approach. In addition, the classification should allow for unambiguous communication of that information to colleagues. Does the current classification, or that evaluated by Drs Yentis and Lee, achieve these goals? Drs Yentis and Lee divided the grade 2 view as previously suggested by other authors [3, 4]. They identified that a subset of grade 2 views are generally easy (2a) and others are more difficult (2b). The incidence of intubation difficulty was significantly greater for grade 2b than for grade 2a (chi-squared with Yates correction, p < 0.0001). Unfortunately, when comparing the incidence of difficulty, they found between grade 2b and grade 3 views that there were too few for useful statistical analysis. Therefore, the data support the view that grade 2 should be divided but does not clearly answer whether the cut-off point between grade 2b and 3 is necessary. In practice, most grade 2 (2a) views can be intubated under direct vision (and are therefore functionally akin to grade 1). In contrast, grade 2b views (where only the posterior part of the glottis is visible) generally require the use of the gum elastic bougie and many grade 3 larynxes can also be intubated with a gum elastic bougie. Although these views are from

different grades, they present similar practical problems. Intubation is not ‘easy’ but neither is it ‘difficult’. Grade 3 views that cannot be intubated with the gum elastic bougie (one might call these 3b) are very difficult and require the same sort of techniques to facilitate intubation that grade 4 views need. This suggests that a division of grade 3 view is also needed and that it would be sensible to group ‘unbougiable grade 3’ with grade 4. This is important because failed intubation is more frequently associated with grade 3 than withgrade 4 views [5], because of the rarity of grade 4 views. I have previously proposed that the grading system be reclassified [3]. The reclassification (Table 1) arose during discussions with Drs Wilson and Nolan and I believe it offers practical benefits that the current system does not. Laryngoscopy where intubation can be achieved under direct vision without aids (grade 1 and 2a) is EASY. Where intubation is best achieved using an indirect method (the gum elastic bougie) but is otherwise straightforward (grade 2b and grade 3 with epiglottis easily lifted), it is RESTRICTED. Finally, when simple indirect methods fail or are inappropriate (grade 3b where the epiglottis is adherent to the posterior pharyngeal wall or only the tip is seen and all grade 4), it is termed DIFFICULT and specialist techniques will usually be required. While this classification does not overcome the problem of the easy laryngoscopic view that presents difficulty due to poor/awkward teeth it does make an attempt to identify both easy and difficult views and to quantify the degree of practical difficulty encountered.



Does the present classification achieve unambiguous communication of the view? Less than 50% of a sample of British anaesthetists were able to correctly classify laryngeal views [6]. Whether this is due to ignorance or ambiguity in the original description is unclear. Firstly, Cormack and Lehane’s paper does not state in the text that the grade is defined by the best view obtained; this information is only in the legend of one of the figures. Second, if anterior laryngeal pressure reveals most of the cords when without it only the arytenoids were visible, is this grade 2 or grade 1? The drawing of grade 3 has small posterior bulges visible behind the epiglottis which could be (mis)interpreted as being the tips of the arytenoids. Cormack and Lehane reported that grade 3 laryngeal view occurred in 1 in 2000 cases but other reports suggest it occurs far more frequently, the incidence in various populations ranging from 1.5 to 10% [4, 7–9]. Division of grade 2 into 2a and 2b improves discrimination in communication but the grading now becomes a five-point system, much of which is redundant. Lastly, one aspect that Dr Yentis and other investigators have not addressed is the degree of difficulty. Intubation is considered as ‘difficult’ or, ‘not’. This dichotomy may be misinterpreted as implying two things that may not be true. Firstly, that in the absence of difficulty, intubation is easy and, secondly, that all difficult intubations are of equal difficulty. In reality, most would recognise a spectrum of increasing difficulty. Yentis and Lee’s criteria for difficult intubation incorporates both cases where a gum elastic bougie makes intubation possible immediately and also those cases where intubation is impossible without specialist techniques. Most truly difficult intubations are grade 3 or 4 while most grade 2b and many grade 3 views merely cause minor inconvenience. I suggest that an easy/restricted/ difficult classification is an improvement on the current classification. I believe the greatest barrier to introducing a new system of classification is the fact that Cormack and Lehane’s system is widely used.


As well as identifying difficulty with intubation, it is helpful if a classification can identify cases where difficulty is extremely unlikely (easy). I am evaluating the proposed classification to determine its sensitivity and positive predictive ability in determining both intubation that is ‘easy’ and ‘difficult’ and hope to publish this in the near future. T. M. Cook Royal United Hospital, Bath BA1 3NG, UK References 1 Cormack RS, Lehane J. Difficult intubation in obstetrics. Anaesthesia 1984; 39: 1105–11. 2 Rose DK, Cohen MM. The incidence of airway problems depends on the definition used. Canadian Journal of Anaesthesia. 1996; 43: 30–4. 3 Cook TM, Nolan JP, Gabbott DA. Cricoid pressure: are two hands better than one? Anaesthesia 1997; 52: 179–80. 4 Wilson ME, Spiegelhalter JA, Robertson JA, Lesser P. Predicting difficult intubation. British Journal of Anaesthesia 1988; 61: 211–6. 5 Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487–90. 6 Cohen AM, Fleming BG, Wace JR. Grading of direct laryngoscopy. A survey of current practice. Anaesthesia 1994; 49: 522–5. 7 Williams KN, Carli F, Cormack RS. Unexpected difficult laryngoscopy: a prospective survey in routine general surgery. British Journal of Anaesthesia 1991; 66: 38–44. 8 Frerk CM. Predicting difficult intubation. Anaesthesia 1991; 46: 1005–8. 9 Rocke DA, Murray WB, Rout CC, Gouws E. Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia. Anesthesiology 1992; 77: 67–73.

A reply Dr Cook is quite right in his summary of the problems defining ‘difficulty’ of intubation and the difficulties classifying the rarer laryngoscopic views. These points are discussed in our paper. The main reason for subdividing the

Cormack and Lehane grade 2 into 2a and 2b is that 2b is awkward and common; since grades 3 and 4 are rare there seems little point in subdividing these grades too. I think that Dr Cook’s proposed easy– restricted–difficult grading confuses laryngoscopic view with difficulty of intubation; what about the grade 4 view which is easily overcome with a bougie passed blindly, or a grade 1 view that requires a bougie? Much better to keep the descriptions of laryngoscopic view and degree of difficulty separate, e.g. ‘grade 4 – easy with bougie passed blindly’ and ‘grade 1 – bougie required’ for the above examples. S. Yentis Chelsea and Westminster Hospital, London SW10 9NH, UK Fracture of the outer varnish layer of a gum elastic bougie

A 50-year-old woman presented for a laparoscopic cholecystectomy. A grade 3 Cormack and Lehane view was obtained at laryngoscopy. A 15-Ch, 60-cm Eschmann bougie was used to assist intubation. The distal end of the bougie was gently bent forwards in an attempt to further angulate the distal segment. This caused a fracture of the outer layer of the bougie at 12 cm from the distal end. The fracture was immediately apparent. The bougie was bent at an angle of less than 90⬚. An attempt was made to pass this bougie into the trachea but this was unsuccessful. The operating department assistant went to an adjoining theatre to obtain a new undamaged bougie. The new bougie was successfully inserted into the trachea resulting in an uneventful tracheal intubation. The original bougie was subjected to further evaluation. Gentle bending of the distal 12-cm segment resulted in a further fracture of the outer layer at 5 cm from the tip. Bending of the proximal section of the bougie at an angle of 180⬚ did not result in any further fracture of the outer coating. It appears therefore that there were localised areas of weakness in the outer layer of the bougie. The damaged bougie was subsequently discarded.

497


A similar problem occurred recently. The trainee was unable to pass a bougie into the trachea but was unaware that the bougie was defective. The consultant then attempted to intubate the trachea. At that time it was noted that the outer layer of the bougie was fractured 10 cm from the tip. The bougie was changed and a further attempt at intubation was successful. Attempts to gently bend both the distal and the proximal sections of this bougie resulted in no further trauma to its outer layer. There has been a previous report of failed intubation with a defective bougie which resulted in a critical incident [1]. In that case, the outer varnish coating broke at a distance of 3 cm from the tip of the bougie. Intubation when using the bougie was unsuccessful but was eventually successful with the help of a stylet in the tracheal tube. The defect in the bougie was not recognised until later. Considering the frequency of use of these devices, it is clear that either this problem is very rare or that incidences of fracture of the outer varnish coating go unreported. Bougies vary considerably in their physical properties. Some are rigid and difficult to bend and some are very floppy. In the manufacturing process, the inner braided layer is impregnated with varnish and the bougie is then placed in an oven to dry. This process is repeated up to five times. There is therefore an art as well as a science component in the manufacturing process. Each bougie is supposed to be used up to five times and then it should be discarded. It appears that this advice is probably ignored by virtually all users. This is partly because there is normally no formal record kept of usage of the device. Also the device will usually function perfectly well for considerably more than five times. What is the indication for changing an old bougie for a new one in clinical practice? This is far from clear. It is also clear that the manufacturers instructions in respect of sterilisation after use are often ignored [2]. In a recent unpublished Cardiff audit of 200 uses of the bougie, there was one case of initial failure because the bougie was judged to be too rigid and one

498

failure where the bougie was judged to be too floppy. In both cases, successful intubation resulted when the bougie was changed. There was only one final case of intubation failure with the bougie in the 200 cases. The intubation success rate was 16/24 cases (66%) when the bougie was used in an Australian series [3]. The comparative intubation success data with use of an introducer in their series was 6/15 cases (40%). It is not clear why our results are so different from theirs. It is clear, however, that there is very little prospective data available on the effectiveness of this device. There are of course a number of case reports and other data supporting its use in the management of cases of unsuspected difficult intubation. We agree with Robbins [1] that bougies should be inspected before use. We would also recommend that users check that they are happy with the rigidity of the chosen bougie and that a spare bougie is readily available. There are no data available on optimum rigidity but it appears that the manufacturers generally get it about right because our incidence of failure was only 0.5%. P. Latto University Hospital of Wales, Cardiff CF4 4XW, UK References 1 Robbins PM. Critical incident with gum elastic bougie. Anaesthesia and Intensive Care 1995; 23: 654. 2 Letheren MJR. Sterilisation of gum elastic bougies. Anaesthesia 1994; 49: 921. 3 Williamson JA, Webb RK, Szekely S, Gillies ERN, Dreosti AV. Difficult intubation: an analysis of 2000 incident reports. Anaesthesia and Intensive Care 1993; 21: 602–7.

Vanner states that assistants can train on weighing scales [1], but we would like to suggest an easier, more accurate and reproducible method to train anyone applying cricoid force. The method requires a fresh Luer lock 50–60-ml syringe (Plastipak, Omnifix, OPS, or Sherwood) which is filled with 50 ml of air. The syringe is then capped and placed upright on a flat surface held steady by the nondominant hand. The thumb, middle and first finger are then placed on the plunger and it is depressed by 12 ml to the 38-ml mark to apply 20 N of force. To achieve 30 N of force, depress by 17 ml to the 33-ml mark. These values are not absolute but, by reviewing the data in the abstract [2], it can be seen to be much more accurate than weighing scales. We have recently completed a research project which shows that this method gives accurate, reproducible cricoid forces when a range of healthcare professionals were trained in its use. M. J. Ruth Royal Infirmary of Edinburgh, Edinburgh EH3 9YW, UK R. Griffiths Peterborough District Hospital, Cambs. PE3 6DA, UK References 1 Herman NL, Carter B, Van Decar TK. Cricoid pressure: teaching the recommended level. Anesthesia and Analgesia 1996; 83: 859–63. 2 Ruth MJ, Griffiths R. Assessment of the 50ml syringe as a simple training aid in the application of cricoid pressure. British Journal of Anaesthesia 1998; 81: 292P.

Safe use of cricoid pressure

Bronchospasm and confirmation of tracheal tube placement

We read with interest the editorial on ‘Safe use of cricoid pressure’ (Anaesthesia 1999; 54: 1–3). My colleague and I agree that anaesthetic assistants must be properly trained in the application of cricoid force, and a truly accurate method has yet to be devised. Dr

I was interested to read the case report by Chan and colleagues (Anaesthesia 1998; 53: 1207–8), in which a patient with severe bronchospasm was thought to have a misplaced tracheal tube due to an absent reading on the capnograph. I had a similar experience a few years ago



having been called to the emergency room to assess a patient with status asthmaticus. The patient was a large teenage girl, known to be a severe asthmatic, who had arrived cyanosed and unconscious. It was assumed that the aetiology of this presentation was a severe asthma attack. She had been intubated promptly by the emergency physician, but there was still concern about proper placement of the tracheal tube as she remained cyanosed, air entry was absent and a blood gas revealed an arterial partial pressure of carbon dioxide above 14 kPa. Capnography was not available in our emergency room at that time. The emergency physician was considering removing the tube as it was felt to be misplaced. I performed a laryngoscopy which confirmed the tube to be in a satisfactory position, and a quick easy pass with a suction catheter indicated no obvious occlusion of the tube. I then noted that the patient was being manually ventilated at a high rate, but not at particularly high airway pressures. By changing the pattern of ventilation to one with a slow rate, long expiratory time and high inspiratory pressures, we were able to detect chest wall movement and breath sounds bilaterally. A chest Xray ruled out a pneumothorax. With the aid of continuous nebulised and intravenous salbutamol, her gas exchange improved quite quickly and she went on to make a full recovery. I was led to wonder what the outcome might have been if the tube had been removed in an acidotic, hypercarbic and hypoxic patient. It is very likely that she would have been impossible to ventilate with a bag and mask. Although the old adage ‘if in doubt, take it out’ is often reasonable, in this case a laryngoscopy and ‘leaving it in’ led to a good outcome. R. G. Cox Alberta Children’s Hospital, Calgery T2T 5C7, Canada Another case of disappearing wheeze

With regards to the article by Murray & Lawler (Anaesthesia 1998; 53: 1006–11),


we should like to discuss a very similar scenario of a 21-year-old female who was admitted to the intensive care unit for ventilatory support on two separate occasions with a provisional diagnosis of acute bronchospasm. She had recently moved to the area and was a presumed asthmatic on regular inhalers, but was not under specialist hospital care. On both occasions, she presented to the Accident and Emergency Department with sudden onset of severe dyspnoea. On examination, she was distressed, unable to talk and was noted to have inspiratory stridor, intercostal recession and no breath sounds on auscultation. There was no wheeze. She was cardiovascularly stable and blood gas analysis showed adequate oxygenation with a slight shunt. In view of her presumed history of asthma, she was aggressively treated on both admissions with nebulised salbutamol and ipatropium, intravenous steroids and an aminophylline infusion. She failed to respond and anaesthesia was induced on both occasions with propofol and her trachea intubated following muscle relaxation with suxamethonium. Immediately, it was noted that her chest was easy to ventilate with normal airway pressure and bilateral air entry. There were no added sounds and blood gas analysis revealed normal gas exchange. On both occasions, following transfer to the intensive care unit, she was extubated within 1 h. However, she continued to complain of dyspnoea and had a persistent mild inspiratory stridor. These symptoms were successfully treated with a low-dose intravenous propofol infusion. On her second admission, a presumed diagnosis of laryngeal dyskinesia or functional psychogenic laryngospasm was made. She was discharged with a letter detailing this diagnosis and guidelines for possible management should she present again in similar circumstances. Subsequent investigations by ENT and respiratory physicians have shown normal lung function and no structural abnormality. Examination of old notes from previous hospital care show multiple similar admissions to intensive care and general medical wards. We wonder how frequently asthma is misdiagnosed in similar

circumstances. Clearly, the diagnosis of functional psychogenic laryngospasm is one of exclusion and should be made by a senior clinician. It should, however, be suspected if the airway obstruction is immediately relieved on induction of anaesthesia. Once the diagnosis is made, the patient must undergo education and receive documentation suggesting a protocol for treatment. A multidisciplinary approach should be adopted involving speech therapists, psychologists, GPs, employers/teachers and family. C. J. Langrish A. McCrirrick Gloucestershire Royal Hospital, Gloucester GL1 3NN, UK An unusual case of stridor

A 17-year-old male, with severe mental handicap and physical deformity due to cerebral palsy was admitted to our hospital for investigation of weight loss and diarrhoea. He was accompanied by his full-time professional carer and continued to spend most of his day in his specially contoured supportive wheelchair. A diagnosis of inflammatory bowel disease was made and treatment started. The response was poor and his condition continued to deteriorate. His serum albumin decreased to 19 g.dlÿ1 and dependent oedema affecting his legs, sacral area and hands became very evident. Oral methylprednisolone was given and, at that time, the carer confined him to bed, feeling that he was too unwell to sit out in his chair. Within 24 h of the first dose of steroids, he developed inspiratory stridor that was associated with obvious oedema of the face and neck. An adverse drug reaction was suspected, the steroids were discontinued and an anaesthetic opinion regarding airway management was sought. Close questioning of the carer revealed that the leg oedema had noticeably reduced with the bed rest and careful inspection showed that the patient’s head and kyphotic chest had sunk the most into the pneumatic mattress. Examination of his head, permanently turned to the left by deformity, revealed extensive pitting oedema which was

499


particularly marked around the dependent eye. It was obvious that redistribution of dependent oedema was a more likely explanation for his stridor than an adverse reaction to methylprednisolone. He was therefore transferred into his wheelchair, which maintained him in a sitting position, and was kept under close observation. The facial oedema and stridor resolved over the next few hours and methylprednisolone was later re-introduced without incident. This unusual case highlights the simple fact that dependent oedema distributes according to gravity rather than anatomy. Dependably dependent oedema. E. W. Moore M. W. Davies Royal Liverpool University Hospital, Liverpool L7 8XP, UK Miller laryngoscope blades

The Miller laryngoscope is known to be a useful tool in difficult tracheal intubation [1]. We have noted a design feature which may be of interest to individuals before purchasing a Miller laryngoscope blade. The light source, which in some designs protrudes beyond the distal margin of the blade, can be obscured by the tongue during attempted laryngoscopy (upper figure). In other designs, however, the light source is protected by the distal aspect of the blade which

500

prevents the tongue from falling across the light source (lower figure). We therefore recommend the use of a Miller laryngoscope similar in design to the one shown in the lower figure. D. Raw A. Skinner Whitston Hospital, Prescot L35 5DR, UK

allowing for adequate ventilation. This manoeuvre is also of help with the more common problem of obtaining a good airway and seal in the edentulous patient whose facial support has been removed with the dentures. J. Crooke Countess of Chester Hospital, Chester, UK

Reference 1 Henderson JJ. The use of paraglossal straight blade laryngoscopy in difficult tracheal intubation. Anaesthesia 1997; 52: 552–60. The bearded airway

Vincent and Ames (Anaesthesia 1998; 53: 1034–5) provide us with a novel but somewhat unwieldy approach to ventilating patients with beards. They highlight the twin problems of obtaining an adequate seal between mask and face, and of maintaining an effective chin lift, in the presence of slippery bristles. An approach taught to me by my anaesthetist father allows for effective ventilation without the need for clingfilm. The lower lip is everted and the caudal rim of the facemask is lowered onto the exposed buccal mucosa, in to the angle between the lip and inferior alveolar ridge. A good seal is thus formed around a significant part of the facemask,

Persistent pruritis after pentastarch infusions in intensive care patients

Following recent controversy over the safety of albumin solutions [1], the use of synthetic colloids has, inevitably, received fresh attention. Clearly, for each of these compounds, the potential benefits have to be weighed against potential risks. Against this background, we would like to report the results of a recent investigation into the incidence of persistent pruritus in intensive care patients who have received pentastarch. Our interest was aroused initially when it was noticed that pruritus seemed to be a relatively common complaint in patients returning, usually at least 2 months postdischarge, to our nurse-led follow-up clinic. In some, it significantly detracted from their quality of life, disturbing sleep and proving totally refractory to all remedies prescribed by their general practitioners. The standard colloid in use on the intensive care unit at the time was 10% ‘HAES-steril’ (Fresenius Kabi, Germany), a hydroxyethyl starch (HES) preparation with a molar substitution of 0.5. Pruritus has been reported following the use of HES solutions [2] and the product data sheet for ‘HAES-steril’ includes among the side-effects persistent, reversible itching ‘in a rare number of cases’. We therefore conducted a retrospective survey to identify the incidence of this problem in intensive care survivors. A postal questionnaire was sent to 100 consecutive adult patients who, over a 6-month period, had been on the intensive care unit (ICU) for more than 24 h. In order to avoid a biased response, only two of the 19 questions asked about itching. The others inquired about general well-being, quality of life, mood and memories of intensive care. The relevant 䊚 1999 Blackwell Science Ltd


questions were ‘have you experienced any itching since your hospital stay?’, with the options of ‘yes’ or ‘no’ as replies, and ‘if so, how would you describe this itching?’, with, as potential replies, ‘slight itch’, ‘moderate itch’, ‘severe itch’ and ‘very severe itch’. Patients either not responding to the questionnaire or who had suffered itching were followed up by telephone. In all who had suffered pruritus, standard questions were asked to identify severity, duration, triggering or relieving factors and the part of the body affected. The ICU charts for all patients were examined to identify whether they had received ‘HAESsteril’ and, if so, the volume involved. Details were obtained from 73 patients. Thirty-four per cent had experienced pruritus since their discharge from the ICU. Of these, 44% had severe, persistent pruritus which had not resolved with conventional treatments. In some it had lasted up to 1 year after the period of intensive care. In patients with pruritus, the total volume of ‘HAES-steril’ received ranged from none (in three patients) to 27.35 l (median 2 l), infused over a median of 2 days (range 1–21 days). In the nonpruritus group, the volume ranged from none (in 10 patients) to 13.35 l (median 0.5 l), infused over a median of 1 day (range 1–9 days). There was a significant relationship between the volume of HES infused and the occurrence of pruritus (p 0.003, Mann–Whitney U-test). The pathogenesis of pruritus following HES has been uncertain, although it is known to correlate well with cumulative dosage and possibly molecular weight [3]. Recent work has implicated the uptake of HES into peripheral nerve Schwann cells, a phenomenon not seen in patients who receive HES without subsequent itching [4]. The same study suggested, furthermore, that perineural release of Substance P may contribute to the symptoms. Other factors, however, must also be implicated, as evidenced by the three patients who suffered itching despite having not received HES. Pruritus following HES is well recognised, although it is generally thought to be uncommon. We have shown that a third of our patients suffered this problem which was severe enough to


detract significantly from their quality of life in many cases. It is a factor which should be taken into account when deciding which colloid is appropriate in the intensive care setting. C. Sharland A. Huggett M. S. Nielson P. S. Friedmann Southampton General Hospital, Southampton SO16 6YD, UK References 1 Cochrane Injuries Group Albumin Reviewers. Human albumin administration in critically ill patients: systematic review of randomised controlled trials. British Medical Journal 1998; 317: 235–40. 2 Speight EL, MacSween RM, Stevens A. Persistent itching due to etherified starch plasma expander. British Medical Journal 1997; 314: 1466–7. 3 Gall H, Kaufmann R, von Ehr M, Schumann K, Sterry W. Persistierender pruritus nach hydroxyathylstarkeinfusionen. Hautarzt 1993; 44: 713–6. 4 Metze D, Reimann S, Szepfalusi Z, Kraft D, Luger T. Hydroxyethylstarch (HES) – associated pruritus as a result of long-term storage in cutaneous nerves. Journal of Investigative Dermatology 1998; 110: 682.

TIVA with propofol and remifentanil

I would like to report an interesting observation made whilst using a TIVA technique with a propofol–remifentanil combination. A 16-kg, 4-year-old girl presented for a routine closure of a soft palate defect. Apart from having 22q deletion syndrome causing mild mental retardation, she was perfectly fit and healthy. Midazolam 8 mg was administered as premedication 30 min prior to surgery. Anaesthesia was induced with 8% sevoflurane in nitrous oxide and oxygen, and venous access was secured, allowing the sevoflurane to be discontinued. A 50-mg bolus dose of propofol was administered, followed by an infusion

at 10 mg.kgÿ1.hÿ1, whilst a concurrent infusion of remifentanil was commenced at 1 mg.kgÿ1.minÿ1. After 60 s, the trachea was intubated without muscle relaxants using a 5.0 RAE tracheal tube. Ventilation was continued with an oxygen/air mixture, using a T-piece system and a Penlon 200 ventilator with a Newton valve attachment. Intra-operative monitoring included ECG, pulse oximetry, noninvasive blood pressure, inspired oxygen and end-tidal carbon dioxide concentration. The operative field was infiltrated with 0.25% bupivacaine and 1 : 200 000 adrenaline. Prior to commencing surgery, the propofol and remifentanil infusions were reduced to 8 mg.kgÿ1.hÿ1 and 0.5 mg.kgÿ1.minÿ1, respectively. Despite the adrenaline infiltration, the initial heart rate was approximately 70–75 beat.minÿ1, with a sinus rhythm on the ECG monitor. The SpO2, FE, CO2 and blood pressure were all normal. Over the next 30 min, the heart rate continued to decrease, reaching a lowest value of 49 beat.minÿ1. Both the propofol and remifentanil infusions had been reduced further, to 6 mg.kgÿ1.hÿ1 and 0.25 mg.kgÿ1.minÿ1, respectively. Close examination of the ECG revealed that the patient had developed a nodal bradycardia. The blood pressure was still well maintained, but in view of the dramatic decrease in heart rate, atropine 0.1 mg was administered. This and a subsequent dose of 0.1 mg had no effect, and therefore a third dose was given. Following this, the heart rate increased to 130 beat.minÿ1 and returned to sinus rhythm. Over the next 45 min, the rate gradually decreased again, but subsequently never went below 100 beat. minÿ1. The anaesthetic proceeded uneventfully and the patient recovered rapidly and without incident. To my knowledge, this is the first report of a significant arrhythmia involving a propofol and remifentanil combination. Both drugs are known to cause a reduction in the heart rate, mainly by altering the balance of vagal and sympathetic tone [1]. Indeed, remifentanil has recently been reported as causing marked sinus bradycardia in patients anaesthetised for cardiac surgery [2]. Propofol has also been associated with prolongation

501


of the QT interval and the appearance of a junctional rhythm at induction [3], although these effects are inconsistent and may be prevented by premedication with atropine [4]. Combinations of propofol with other opioids such as fentanyl, alfentanil and sufentanil appear to give rise to more frequent and more severe episodes of bradycardia [5–7]. It is interesting that local infiltration with adrenaline did not lead to a noticeable increase in the heart rate. My clinical impression is that by using a propofol and remifentanil combination for maintenance of anaesthesia, tachycardia following infiltration is less frequent and less marked than when using a volatile agent. It seems that the only reliable means of preventing significant bradycardia or A–V nodal conduction problems in this situation is with the use of an anticholinergic, either as premedication or intravenously at the time of induction. O. Bagshaw The Birmingham Children’s Hospital, Birmingham B4 6NH, UK References 1 Deutschman CS, Harris AP, Fleisher LA. Changes in heart rate variability under propofol anesthesia: a possible explanation for propofol-induced bradycardia. Anesthesia and Analgesia 1994; 79: 373–7. 2 DeSouza G, Lewis MC, TerRiet MF. Severe bradycardia after remifentanil. Anesthesiology 1997; 87: 1019–20. 3 Saarnivaara L, Hiller A, Oikkonen M. QT interval, heart rate and arterial pressures using propofol, thiopentone or methohexitone for induction of anaesthesia in children. Acta Anaesthesiologica Scandinavica 1993; 37: 419–23. 4 Hiller A, Klemola UM, Saarnivaara L. Tracheal intubation after induction of anaesthesia with propofol, alfentanil and lidocaine without neuromuscular blocking drugs in children. Acta Anaesthesiologica Scandinavica 1993; 37: 725–9. 5 Hug CC Jr, McLeskey CH, Nahrwold ML, et al. Hemodynamic effects of propofol: data from over 25,000 patients. Anesthesia & Analgesia 1993; 77: S21–9. 502

6 Hiller A, Saarnivaara L. Injection pain, cardiovascular changes and recovery following induction of anaesthesia with propofol in combination with alfentanil or lignocaine in children. Acta Anaesthesiologica Scandinavica 1992; 36: 564–8. 7 Egan TD, Brock-Utne JG. Asystole after anesthesia induction with a fentanyl, propofol, and succinyicholine sequence. Anesthesia and Analgesia 1991; 73: 818–20. 8 Jensen AG, Granfeldt H, Kaiman SH, Nystrom PO, Eintrei C. A comparison of propofol and isoflurane anaesthesia: the need for ephedrine and glycopyrrolate. European Journal of Anaesthesiology 1995; 12: 291–9. The uptake of sevoflurane

The breathing system used by Drs Vagts and Lockwood (Anaesthesia 1998; 53: 862–6) is inherently unsatisfactory for the investigation described. The system described in their figure 1 may often behave like a closed system but it is not. If a leak develops, the ventilator drive gas will make up the deficit, but if there is an excess of respirable gas, this will escape through the ventilator taking anaesthetic agent with it. In order to obtain accurate measurement of anaesthetic agent uptake, it is essential to physically isolate the ventilator drive gas from the respired gas by an impermeable membrane which can be seen. If a ‘bellows-inbottle’ is used and the bellows rise to the same point on each expiration (preferably just short of the top of the available travel), it is possible to confirm gastightness of the system. In addition, the oxygen uptake of the patient can also be measured. Only if oxygen uptake is within expected limits can the agent uptake measurement be assumed to be valid. ‘Bellows-in-bottle’ ventilators are readily available. Why did these authors not use one? The study should be repeated with appropriate equipment. A. McHutchon Queen Elizabeth Hospital, Gateshead NE9 6SX, UK

A reply Thank you for the opportunity to comment on Dr McHutchon’s letter. He

correctly identifies two potential problems with anaesthetic systems using trunk ventilation. If there is a leak in the breathing system, ventilator drive gas makes up the deficit and in our system this would result in an increased inspired oxygen concentration. As we state in the Methods section, that did not occur. The second point does not apply to our system, because the only respirable gas supplied to the breathing system is via the trunk. The alternative system he proposes could certainly be used, but uptake of anaesthetic into the rubber of the bellows is a complicating factor. Such an arrangement would require the same measurements of loss that we have undertaken with ours [1]. In addition to this point, we did not have ready access to an anaesthetic machine with a leak-free bellows-in-bottle ventilator and a low-flow oxygen Rotameter when we began the series of studies [2], which partly explains our adoption of this system. Finally, we welcome other studies of anaesthetic uptake, which does not seem to attract the amount of interest we think it warrants. If Dr McHutchon has suitable equipment readily available, we encourage him to perform and validate measurements of uptake in his patients. G. Lockwood Hammersmith Hospital, London W12 0HS, UK References 1 Vagts DA, Lockwood GG. The loss of sevoflurane from a closed breathigng system. Anaesthesia 1997; 52: 636–9. 2 Lockwood GG, Chakrabarti MY, Whitwam JG. A computer controlled anaesthetic breathing system. Anaesthesia 1993; 48: 690–3.

Self-administration of preoperative analgesic suppositories

I read with interest Dr Jolliffe’s correspondence (Anaesthesia 1998; 53: 91) on self-administration of pre-operative 䊚 1999 Blackwell Science Ltd


analgesic suppositories to his day case gynaecology patients to avoid the problems of forgetting to consent them for suppository insertions under general anaesthetic. My question is why not use oral self-administration? I find the practice of rectal administration of analgesic is becoming very common and yet there is no documentation of any considerable advantage of rectal administration over oral administration of analgesics. Though no studies have been conducted comparing the analgesic effectiveness of the two routes, my anecdotal observation in paediatric adenotonsillectomies is that the pain relief is of similar duration and effectiveness. In addition, oral administration is acceptable to all patients, and has a better bioavailability than rectal administration [1]. The medicolegal problems associated with rectal suppositories are also well known. Gastrointestinal ulceration and bleeding as complications of administration of nonsteroidal anti-inflammatory drugs occur regardless of route of administration [2]. The only drawback to oral administration is that the stomach may not be empty; but that is so for all oral premedications. A. Asumang Southampton General Hospital, Southampton SO16 6YD, UK References 1 Davies NM, Anderson KE. Clinical pharmacokinetics of diclofenac. Therapeutic insights and pitfalls. Clinical Pharmacokinetics 1997; 33: 184–213. 2 The Royal College of Anaesthetists. Guidelines for the Use of Non-Steroidal Anti-Inflammatory Drugs in the Perioperative Period. Quick Reference Guide January 1998. Software safety and the Diprifusor

I read with great interest the article by Gray and Kenny describing the development of the Diprifusor (Anaesthesia 1998; 53 (Suppl. 1): 22–7). It is encouraging to see the extent to which the manufacturer has gone in attempting to


achieve safety in the device. I note with concern that a potential problem appears to have been overlooked in the development of the software. The authors state that as the Diprifusor uses a second microprocessor to check the results of the first, a simultaneous failure is unlikely. The argument given is that the two microprocessors are made by different manufacturers, and require different compilers. The use of so-called N-level programming is not sufficient to prevent common mode software failures, and there is in fact good evidence that programs written to perform a given task by people who do not even know of each other contain similar errors [1, 2]. Leveson [1] goes so far as to say that it is ‘Foolhardy to design process-control systems that rely solely on the proper functioning of software to maintain safety’. Writing two programs to perform the same task increases the complexity of the system, and makes it more likely that at least one of the programs will suffer an error. Even if the programs do not contain similar mistakes, common mode failures could still be present as the pharmacokinetic models used by the processors are the same, and the Diprifusor module does not stop the infusion itself, but rather relies on the pump stopping when the module indicates an error condition. Given the complexity of the underlying algorithm, it is understandable that the manufacturers opted to use software to check the results of the primary processor. To ensure safety, however, it would be preferable to use a hardware solution both as a crude check on the output of the pump, and to limit its maximum rate. J. L. Derrick Prince of Wales Hospital, Shatin, Hong Kong, PRC References 1 Leveson NG. Software safety in embedded computer systems. Communications of the ACM 1991; 34: 34–46. 2 Pamas DL, van Schouwen AJ, Kwan SP. Evaluation of safety-critical software. Communications of the ACM 1990; 33: 636–48.

A reply Thank you for the opportunity to reply to the points raised in the letter from Dr Derrick. While it is possible that programs written to perform the same task by different programmers contain similar errors, that is not the situation in the Diprifusor. The two microprocessors do not perform the same task but undertake completely different tasks from each other. Although both microprocessors are solving the same three-compartment model using the same microconstants, the mathematical solutions are totally different. One microprocessor instructs the infusion pump to infuse at a certain rate and uses one solution to the pharmacokinetic model to calculate the change in calculated blood concentration of propofol. The second microprocessor, in contrast, obtains its data input independently, directly from the pump motor and calculates the precise volume delivered by the pump. This volume is passed to different mathematical equations to those used in the first microprocessor and the resultant concentration is calculated. The two concentrations are exchanged between the microprocessors and each microprocessor carries out a simple (easily validated) comparison. Because of the different tasks undertaken by the two microprocessors and the different pharmacokinetic model solutions used in each, there will be a small difference in the values calculated by each microprocessor but the values must be within a narrow range of each other or the system will shut down. Dr Derrick is correct in that this approach will increase the risk of the system failing by generating an error but he is incorrect in then deducing that this will render the system less safe. The limits used by the Diprifusor are sufficiently broad to maintain reliability whilst providing the safety required for the administration of propofol. A rate-limiting system would be completely inappropriate in this application since the required infusion rates will vary so widely (0.1–1200 ml.hÿ1) as the concentration is titrated to the appropriate clinical level. As well as providing an adequate safety function the operation of

503


the two-microprocessor solution chosen for Diprifusor was relatively easy to validate and communicate to the regulatory authorities – an increasingly important consideration. In summary, the two microprocessors do not undertake the same tasks. The pharmacokinetic model solutions and resultant mathematical equations used by the two microprocessors are not the same. It would require an error in the software used by the first microprocessor to produce an exact calculated propofol concentration which matched another entirely different software error in a different microprocessor which had acquired its input data in a completely different manner and used a different series of equations to produce the same incorrect answer. While an infinite number of monkeys may eventually type out the entire works of Shakespeare without any error, the probability is low. G. N. C. Kenny University of Glasgow, Glasgow G31 2ER, UK Accidental switch-off of an anaesthetic machine

A 45-year-old day-case ASA I female smoker was anaesthetised with propofol 150 mg, fentanyl 75 mg and droperidol 1.5 mg for a transcervical resection of endometrium. Following induction, anaesthesia was maintained with an oxygen/nitrous oxide/isoflurane gas mixture, and she was allowed to breathe spontaneously through an LMA attached to an Excel 210 anaesthetic machine via an Ohmeda circle and 7800 ventilator/ spirometer/minute volume and inspired oxygen monitoring system. As the surgical procedure began, the patient coughed and developed laryngeal spasm. Ventilation was difficult via the LMA and so it was removed and respiration supported with mask CPAP to maintain oxygenation and deepen anaesthesia. As the anaesthetist pulled the circle system towards the patient to facilitate simultaneous airway management and manual ventilation, the machine shut-off alarms sounded and there was a loss of electrical power to the Ohmeda 7800 ventilation monitoring system and total failure of

504

the fresh gas supply into the circle. On looking at the machine, it was observed that the on/off switch located just below the work top had switched to the ‘off ’ position, apparently having been struck by the corner of a Pall BB50T breathing system filter fitted to the expiratory limb of the circle at the absorber head. On returning the switch to the ‘on’ position, there was complete restoration of the lost gas and electrical power and the case continued uneventfully. After the case, the machine was closely inspected. Although the machine in question was fitted with a protective circumferential guard around its rotational master switch, this guard had not been sufficient to protect the machine from being accidentally switched off. On reproducing the incident, it was obvious that the operator-set vertical height of the absorber assembly and the rotational orientation of the filter had been such that the filter’s corner was able to intrude into the space between the guard and rotational switch, push the side of the switch, and cause it to rotate anticlockwise to an ‘off ’ position. However, on examining other Excel machines in our department we were concerned to note that several machines lack even this simple guard around their master switch, and so presumably would be even more vulnerable to such a problem occurring. Indeed in 1992, a similar case was reported when an Excel 210 was switched off when the master switch was struck by the anaesthetist’s chair [1]. This other case, like ours, occurred during management of a ‘critical incident’ when the anaesthetist’s attention was directed elsewhere. Therefore, it would appear that the circumferential guard around the master switch of the Ohmeda Excel anaesthetic machine may not on its own be sufficient to protect the switch from accidental switch-off in circumstances when other equipment deliberately or accidentally intrudes into the space between guard and switch. Therefore, perhaps all master switches on ‘mission-critical’ healthcare equipment also need to be protected by a cover placed over the switch which has to be ‘removed’ to allow switch-on, and more importantly switch-off. Several ITU ventilators

already utilise such a system. In addition, although we no longer use breathing system filters at this position to protect the absorber and anaesthetic machine, this case does demonstrate once again that making apparently simple modifications to our machines may lead to unexpected dangers which may compromise patient safety. A. L. Ronald Aberdeen Royal Infirmary, Aberdeen AB25 2ZN, UK Reference 1 Pomykala Z, Schhechter H. Design flaw in an anaesthetic machine. Anesthesiology 1992; 77: 399.

A reply from the manufacturer The Datex-Ohmeda Excel anaesthetic system has been in use for over 12 years, and has proved to be a safe and effective design. This design incorporates several safety features, including operation of the oxygen failure alarm when the system on/off switch is turned off. However, as noted in the letter, several years ago Datex-Ohmeda became aware of an event where despite a rotational switch design and recessed location under the table top, accidental operation of the system on/off switch occurred. While the machine alarmed and the machine could be readily reactivated by turning the switch on, such that the patient safety was maintained, DatexOhmeda added a guard to further production units in response to customer request and promotion of customer satisfaction. However, since that time Datex-Ohmeda had not received further reports of accidental switch operation, with the guarded or unguarded design, until this letter was received. Datex-Ohmeda conducted a detailed review of this new report, and while we understand that an accidental operation of the system switch occurred, we found the described placement of the breathing circuit surprising as it was located in front of the anaesthesia system which we believe makes the system controls harder to access and use. This is not a configuration we would normally expect or recommend, as it not only potentially limits access to system controls, but also



limits the access to emergency controls such as oxygen flush and the system on/off switch. Therefore, we would normally not have expected this breathing system orientation to represent a practical application of the machine, and this would have more reasonably represented a possible location of the breathing system during movement of the machine between cases. Regarding the comment that the anaesthesia system could have a covered switch similar to ones observed on ITU ventilators, Datex-Ohmeda believes that the application of covers on ITU ventilator controls is primarily intended to prevent the movement of controls by unauthorised personnel such as visitors. This risk has been well publicised, and the attended application of ITU ventilators makes this most appropriate. However, for attended use machines such as an anaesthesia delivery system, the intent of a cover would be to prevent entry to an area that must not be accessed by the user (e.g. service controls), protecting areas that are mechanically vulnerable to damage, or protecting areas vulnerable to undetected accidental changes. We find that none of these situations applies to the reported event, and the fundamental controls to prevent accidental operation of the system switch are careful placement and configuration of the equipment by the operator, careful use of the equipment appropriate for sensitive medical devices, and attended vigilant use. We believe these controls are reasonable to expect, especially considering the level of expertise and training required of practitioners. Datex-Ohmeda, Madison, WI 53707–7550, USA Oxygen failure warning devices

Catastrophic failure of an anaesthetic machine’s oxygen supply is a rare but very serious problem. Its occurrence must be made immediately obvious to the anaesthetist because correct management involves maintaining continuous adequate ventilation of the lungs and using an alternative source of oxygen, either from the machine’s oxygen


cylinder backup or another source. Diagnosis of machine oxygen failure and its management must take suitable priority over any other part of a critical incident, particularly because a slow diagnosis may lead to other alarm states, such as arterial desaturation, with quite long differential diagnoses. Critical incidents involving multiple machine alarm states can take several diagnostic and management loops to control. Unfortunately, anaesthesia machines do not have identical alarms for oxygen failure warning. In addition, on some machines, the audible alarm warning of oxygen failure is not unique to that critical failure. Finally, on some anaesthetic machines with electronic oxygen failure warning devices, failure of the device may not necessarily cut off the supply of anaesthetic gases to the common gas outlet. For instance, the recently introduced Ohmeda 7900 ventilator, integral to some Ohmeda Excel and Modulus anaesthetic machines, has an oxygen failure warning alarm that has the same tone and pattern as any of the other ‘high-priority’ ventilator alarm states, merely somewhat louder. This is worrying because the ‘high-priority’ alarm is frequently activated during anaesthesia for a number of reasons, particularly with earlier versions of the ventilator alarm software. Second, on anaesthesia machines which use the Ohmeda 7900 ventilator, the oxygen failure warning alarm is integral to the ventilator. Under some circumstances, electric supply failure to the Ohmeda 7900 ventilator may result in a fault state in which the anaesthesia machine can continue to deliver anaesthetic gases without an oxygen failure warning device. Discussions with colleagues in several anaesthesia departments have revealed that many anaesthetists continue to expect (erroneously) that oxygen failure warning alarms will have a distinctive continuous sound, unique to oxygen failure. That this is not part of current standards needs to be highlighted, particularly because the guidelines of the Association of Anaesthetists’ ‘Checklist for Anaesthetic Apparatus 2, 1997’ no longer recommends disconnection of

the pipeline oxygen supply in the routine checking procedure. N. Fauvel Chelsea and Westminster Hospital, London SW10 9NH, UK

A reply from the manufacturer The Datex-Ohmeda anaesthesia workstation oxygen supply failure alarm referenced in this letter was developed to meet, and fully complies with, the oxygen supply alarm requirement of European Normative EN 740 (Anaesthetic Workstations and Their Modules Particular Requirements) clause 51.103.1, and European Normative EN 475 (Medical Devices – Electrically generated alarm signals). Under the European Community Medical Device Directive requirements which were fully enacted into law within the member states on 14 June 1998, new medical devices introduced by manufacturers are required to meet the requirements of the applicable European Normative standards. The required characteristics of anaesthesia workstation high-priority alarms is fully defined in these referenced standards, and the Datex-Ohmeda anaesthesia workstation detailed is in full compliance with these requirements. In the event of a failure of the oxygen supply, the Datex-Ohmeda anaesthesia workstation activates a high-priority alarm, which is defined by the standards as an alarm that requires immediate user intervention. High-priority alarms are required to have audio characteristics to uniquely identify them as conditions requiring immediate user intervention. The Datex-Ohmeda high-priority alarm complies with this audio requirement, and a ‘No O2 pressure’ high-priority alarm message is displayed on the 7900 detailing the exact cause of the alarm. This alarm functionality and high-priority characteristics are fully detailed in the Operation and Maintenance manual. Further, verifying the correct operation of the oxygen supply failure alarm is a required test during the Datex-Ohmeda preuse checkout of the anaesthesia system, and is documented in the pre-operative checkout section of the Operation and Maintenance manual, as well as on a laminated card to be kept with the system.

505


With the detailed information provided in the user manual, the clear visual message text describing ‘No O2 pressure’, and the requirement to activate the oxygen supply failure alarm as part of the preuse tests, Datex-Ohmeda believes that the practitioner operating the machine will be able to discriminate the presence of a high-priority oxygen supply failure alarm. The second point in the letter details a concern with the electrical functionality of the anaesthesia workstation. In the event of an electrical system failure there are several control measures, system features, and alarms that have been specifically designed to achieve the functionality and safety aspects required by the European Normative standards. The primary system feature to address the risks of power failure is a back-up battery in the 7900 ventilator that will continue full system operation for at least 30 min, allowing the practitioner time to remedy the situation. Datex-Ohmeda, Madison, WI 53707-7550, USA Monitoring patients with long bone fractures

Clinical signs in hypoxia can be unreliable and nonspecific in certain situations. A 23-year-old Caucasian woman was scheduled for intramedullary nail insertion for a tibial fracture which she had sustained 12 h earlier. There were no other significant injuries. During the on-ward pre-operative consultation, the patient was fully orientated and in no distress. She had received Cyclimorph 10 mg intramuscularly 1 h earlier. Her only history of note was pulmonary tuberculosis 5 years previously, which had been successfully treated. On examination, she had a tachycardia of 108 beat.minÿ1, a respiratory rate of 16 and blood pressure was 120/84 mmHg. Cardiorespiratory examination was otherwise unremarkable. Her chest Xray was normal. On arrival in the induction room 1 h later, pulse oximetry revealed an oxygen saturation (SpO2) of 69% on room air. As before, the patient was conversing

506

normally and had no signs of respiratory distress. Analysis of an arterial blood sample taken while the patient was breathing room air yielded the following results: pH 7.45, PCO2 4.96 kPa, PO2 5.3 kPa, HCO3 26.4 mmol.lÿ1, SaO2 77%. The presumptive diagnosis was fat embolus syndrome (FES). The patient required 60% oxygen via facemask postoperatively to maintain SpO2 > 95%. She was discharged 11 days later. Fat embolus syndrome develops in 5– 10% of patients with multiple long bone or concomitant pelvic fractures [1, 2]. It has been suggested that patients at risk of FES should be monitored with continuous pulse oximetry or with daily arterial blood gases [3]. However, many hospitals do not have sufficient equipment or personnel to follow these recommendations. Perhaps it is time to formalise monitoring guidelines in FES and implement a minimum monitoring standard for patients at risk. Earlier diagnosis would allow the commencement of supplementary oxygen therapy pre-operatively and facilitate the planning of appropriate peri-operative care and monitoring. D. F. O. Croinin J. Loughrey M. Donnelly Tallaght Hospital, Dublin 24, Ireland References 1 Eddy A, Rice C, Carrico C. Fat embolism syndrome: monitoring and management. Journal of Critical Illness 1987; 2: 24–37. 2 Muller C, Rahn B, Pfister U, Mening R. The incidence, pathogenesis and diagnosis and treatment of fat embolism. Orthopaedic Review 1994; 23: 107–17. 3 Ten Duis HJ. The fat embolism syndrome. Injury 1997; 28: 77–85.

Peri-operative management of atrial fibrillation

I read with interest the review article ‘The peri-operative management of atrial fibrillation’ by Nathanson and

Gajaraj (Anaesthesia 1998; 58: 665–76). However, I was surprised to find that there was no mention of the common finding of the acute onset of atrial fibrillation peri-operatively associated with severe abdominal sepsis. Some years ago we presented a study entitled ‘Atrial fibrillation is an ominous sign of the onset of severe MODS in hepato-biliary pancreatico, GIT sepsis’ [1]. Patients had no previous history of atrial fibrillation, no electrolyte or acid– base imbalance nor thyroid function abnormality. Atrial fibrillation developed in 22% of patients during the operative procedure, 44% developed it within 2 h of completion of the procedure and 34% developed it within 48 h of surgery. All the patients developed multi-organ dysfunction and had to be admitted to the ICU. Atrial fibrillation was initially controlled with digoxin which in most of the cases was not satisfactory and at times verapamil was added as a bolus if the blood pressure was stable. Cardioversion lasted only a few hours. Adenosine produced sinus arrest in practically every case we used and should never be used in atrial fibrillation with sepsis; the best results were obtained with amiodarone (bolus 5 mg.kgÿ1 followed with an infusion for 2–3 days). The secret of treating atrial fibrillation associated with sepsis is to control the whole sepsis syndrome. Appropriate antibiotics, volume resuscitation, inotropes/ vasodilators/vasoconstrictors as the case may be, ventilation/oxygenation and the use of drugs like amiodarone to control atrial fibrillation. With such a strategy, the atrial fibrillation disappears in 24–48 h. In patients with sepsis, 40% have cardiovascular dysfunction [2] with reduced ejection fraction [3]. In our study, 24% of patients had right ventricular dilatation. The classification of ‘secondary’ cardiomyopathies is based on ‘myocardial damage within the scope of a systemic disease’. Myocardial impairment in sepsis and the multi-organ dysfunction syndrome might be considered a secondary cardiomyopathy [4]. Atrial fibrillation in abdominal sepsis is an ominous sign of severe inflammatory response, with septic cardiac failure



and early institution of aggressive and appropriate therapy is essential to save the patient. S. Anandaciva Tuen Men Hospital, Hong Kong, PRC

large intra-operative blood loss, should receive a second dose of steroids. E. F. Ratner J. G. Brock-Utne Stanford University Medical Center, Stanford, CA 94305–5640, USA

References 1 Anandaciva S, Vasantha Mailiga. A, Que TL. Atrial fibrillation, an ominous sign of the onset of severe sepsis in hepatico-pancreatico, GIT sepsis. Proceedings of the 2nd South Asian Congress of Anaesthesiologists, 1995. 2 Hess ML, Hastello A, Greenfield LJ. Spectrum of cardiovascular function during gram negative sepsis. Progress in Cardiovascular Disease 1981; 23: 279–98. 3 Waley KR. Ventricular dysfunction during sepsis. Yearbook of Intensive Care and Emergency Medicine. Springer, 1995 4 Werden K, Muller U, Reithmann C. Pathophysiology of Shock, Sepsis, and Organ Failure. Berlin: Springer, 1993; 787–834.

Peri-operative steroid supplementation

We read with interest the review article entitled ‘Peri-operative steroid supplementation’ by G. Nicholson et al. (Anaesthesia 1998; 53: 1091–104). The authors do not specifically mention the use of a potential life-saving second dose of steroids in these patients. We recently had a patient with long-term steroid treatment for chronic obstructive airways disease [1]. The patient underwent an excision of a transitional cell bladder tumour. Despite pre-operative treatment with the recommended dose of glucocorticoids, vascular collapse occurred in the setting of massive haemorrhage even after adequate volume resuscitation. Furthermore, vasoactive agents proved unsuccessful at restoring vascular tone until an additional dose of hydrocortisone was administered. This repeat dose caused an immediate and sustained improvement in arterial blood pressure. We believe that patients receiving chronic steroid therapy, who sustain a 䊚 1999 Blackwell Science Ltd

References 1 Ratner EF, Allen R, Mihm FG, Brock-Utne JG. Failure of steroid supplementation to prevent operative hypotension in a patient receiving chronic steroid therapy. Anesthesia and Analgesia 1996; 82: 1294–6.

We read with interest the recent review article by Nicholson et al. (Anaesthesia 1998; 53: 1091–104) on peri-operative steroid supplementation. Though very thorough, the review does not give a mechanism by which a lack of endogenous cortisol causes sudden cardiovascular collapse. A hypothesis for the action of hydrocortisone at a molecular level was put forward as long ago as 1966, in a paper by Besse and Bass [1]. They presented animal evidence indicating that hydrocortisone produces an increase in the sensitivity of aortic vascular smooth muscle to catecholamines by modifying the interaction of catecholamine with its specific tissue receptor. This potentiation was obtained for both the a- and b-adrenergic effects of catecholamines in vivo and in vitro. More recently, a paper by Steiner et al. [2] in 1988, again from animal work, suggested the stimulation of the phosphoinositide signalling system as a possible mechanism for glucocorticoid action in smooth muscle cells, which may influence intracellular free calcium and thus vascular reactivity and blood pressure. Is this the mechanism by which the lack of cortisol causes cardiovascular collapse in an Addisonian crisis? S. Poulter S. Morris Llandough Hospital, Cardiff CF64 2XX, UK References 1 Besse JC, Bass AD. Potentiation by hydrocortisone of response to catecholamines in vascular smooth

muscle. The Journal of Pharmacology and Experimental Therapeutics 1966; 154: 224–38. 2 Steiner A, Vogt E, Locher R, Vetter W. Stimulation of the phosphoinositide signalling system as a possible mechanism for glucocorticoid action in blood pressure control. Journal of Hypertension (Suppl.) 1988; 6 (4): S366–8. Parents at induction

In a recent letter (Anaesthesia 1999; 54: 91), Dr Lake suggested that the issue of parental presence at induction of paediatric anaesthesia should be considered on the basis of evidence-based practice. Unfortunately, the letter provides a very selective review of the evidence available, and to that extent is potentially misleading. One of the references cited to support the notion that the need for parental presence should be reconsidered [1] is itself a letter. That letter was a response to the publication of a randomised controlled trial [2], which Dr Lake does not cite. Furthermore, the authors of the letter were very strongly rebuked at the time by the principal author of the controlled trial. I have performed a literature review on this subject and identified nearly 30 references. If readers, including Dr Lake, would like to analyse this subject in depth I will be happy to provide them with those references. M. P. Down Dryburn Hospital, Durham DH1 5TW, UK References 1 Pond WW, Aiken JM. Parental presence not necessary during induction of anesthesia. Anesthesiology 1996; 85: 1212. 2 Kain ZN, Mayes LC, Caramico LA, et al. Parental presence during induction of anesthesia: a randomized controlled trial. Anesthesiology 1996; 84: 1060–7.

The presence of parents in the anaesthetic room will always be a thorny subject. It is certain that, in most cases, no problems arise, but as Dr Lake suggests (Anaesthesia 1999; 54: 91) there is some concern that 507


the behaviour of children may be adversely affected by their parents, an issue which has been previously highlighted by Seddon [1, 2]. The move to allow parents into the anaesthetic room has been largely nurse led, on the grounds that it is of benefit to the child. However, there is a lack of convincing evidence to prove that this is the case. Where this research has been conducted, it appears to have relied on subjective opinion and physiological measurement rather than actually asking the opinion of the child involved. Surely, the prime concern is one of safety. The anaesthetist has overall responsibility for the safety of the patient, and anything which that anaesthetist regards as prejudicial to that safety should be excluded. If they feel that admitting the guardian of a child into the already cramped space of the anaesthetic room at an already stressful time may distract them from this prime purpose, then exclusion must be allowable. There is anecdotal evidence that theatre staff also find the presence of parents distracting at times. Several parents have confided in me that they didn’t wish to come, but had felt ‘bullied’ into doing so. Furthermore, who is ultimately responsible for the safety of the parent in this environment? What would be the outcome of a lawsuit from a parent who had suffered injury in an anaesthetic room? My own practice is to allow parents access only if they are accompanied by a member of the ward staff until the child is anaesthetised. The ward staff can then escort the parent out at an appropriate time. This allows the theatre staff to concentrate on the safety of the patient at all times. It may also avoid other problems, such as unchaperoned parents wandering into other clinical areas by mistake, or the supervision of parents with Munchausen by Proxy [3]. Unfortunately, it appears to be impossible to discuss these issues sensibly in the nursing press without meeting a vitriolic antidoctor response [4, 5]. Perhaps this is a fitting subject for the Association to address in one of its guideline publications. J. Watt Burnley General Hospital, Burnley, Lancs, UK 508

References 1 Seddon S. Should parents accompany children to the anaesthetic room? Midlands Medicine 1994; 19: 116–7. 2 Seddon S. Parents in the anaesthetic room? Anaesthesia 1995; 50: 368. 3 Watts J. Parental presence during induction of anaesthesia. Anaesthesia 1997; 52: 284. 4 Watts J. Anaesthetic unit not for parents. Nursing Times 1995; 91 (36): 22. 5 Watts J. Views on parental presence in the recovery room. Nursing Times 1995; 91 (44): 23.

Spinal anaesthesia in the elderly

I was interested to read the letter of Monagle et al. (Anaesthesia 1999; 54: 94–5). Their audit revealed just two postdural puncture headaches (PDPHs) in 275 elderly (> 60 years) patients after spinal anaesthesia, the majority performed with Quincke needles. I performed a survey of 120 patients some years ago. At the time, all nonobstetric spinal anaesthesia was performed with Quincke needles of 22, 25 or 26 gauge. Patients were seen when ambulant. Five patients were deemed to have PDPH (judged primarily by the postural nature). All five spinals were successful at the first attempt, three with 22 gauge and two with 26 gauge needles. Interestingly, four occurred in male urology patients aged 71–80 years. All five patients were out of bed on the first postoperative day. As a result, I recommended avoidance of 22 gauge Quincke needles in patients expected to be mobile in the early postoperative period, irrespective of age. Unfortunately, the survey is yet to be repeated. Mongale et al. state that all their patients were ambulant within 7 days. I would be interested to know what proportion were ambulant much earlier than this, as it appeared to be an important factor in the development of PDPH in my own survey. C. Brocklehurst Royal Oldham Hospital, Oldham OL1 2JH, UK

A reply I thank Dr Brocklehurst for his interest. In response to his question, it is the usual practice in our institution to mobilise patients as soon as is practical after spinal anaesthesia. There appears considerable evidence that recumbency does not prevent PDPH and only delays the onset [1, 2]. Geilen goes on to say ‘patients should be allowed to ambulate as soon as motor function permits’. Of the 126 urology patients in our survey, 115 were ambulant on day 1 postoperatively, with the remainder ambulant by day 3. Of the 97 orthopaedic patients, 17 were ambulant on day 1, 64 by day 3 and the remainder by day 7. Our experience would support the view that mobilisation does not influence the incidence of PDPH. J. Monagle Peninsula Healthcare Network, Frankston 3199, Victoria, Australia References 1 Geilen M. Post dural puncture Headache (PDPH): a review. Regional Anaesthesia 1989; 14: 101–6. 2 Weeks SK. Spinal headache – prevention and treatment. Canadian Journal of Anaesthesia 1990; 37: Sliii– Slviii.

Spinal before epidural single interspace CSE technique for labour

Compared with single modality techniques, the combined spinal and epidural (CSE) method of providing regional anaesthesia has a number of important advantages [1]. The spinal injection provides analgesia of rapid onset, whilst epidural catheter placement provides the ability to extend or prolong the block. Thus, it is no longer necessary to use large initial doses of intrathecal drugs to ensure adequate anaesthesia, hence avoiding unwanted cardiovascular effects of high spinal blockade, such as hypotension. These properties of CSE have led to the technique’s recent increase in popularity, especially in obstetric anaesthesia practice where rapid and extendable analgesia without hypotension are desirable. 䊚 1999 Blackwell Science Ltd


The emergence of CSE as a popular technique appears to stem from the development of small pencil-point spinal needles that cause less headache and greatly reduce the chance of inadvertent epidural catheter placement into the subarachnoid space via the dural puncture hole [1]. Several methods have been described for the performance of CSE. Classically, two lumbar spine interspaces are used, with the epidural catheter being placed first via a Tuohy needle, followed by intrathecal puncture and injection. This enables a test dose to be given to check the position of the epidural catheter before performing the spinal. More recently, the single lumbar interspace needle-throughneedle method has been described, which involves first inserting the Tuohy needle, then performing the spinal injection using a ‘needle-through-needle’ technique and finally placing the epidural catheter. An extra-long spinal needle or special CSE kit is required, of which several are now sold. However, the needle-through-needle technique has several potential complications. The spinal needle, especially when fine bore (27 gauge), is liable to kink as it passes through the hub of the Tuohy needle. Hence, cerebrospinal fluid flow via the spinal needle may not be detected, leading to uncertainty as to whether it has punctured the dura and entered the subarachnoid space. The spinal needle may also form a tract which the epidural catheter may follow into the subarachnoid space. To overcome these potential problems needle-beside-needle techniques have been developed and several specialised kits are also now available. However, the needle-beside-needle technique is also not without its problems. In addition to the need for specialised kits, the epidural space also has to be identified first, as with the ‘needlethrough-needle’ technique, prior to performing a spinal injection. Furthermore, in both these techniques, the Tuohy needle can become dislodged during the insertion of the spinal needle, resulting in inadvertent dural puncture. In the labouring woman, the problem of inadvertent dural puncture may be accentuated due to excessive patient movement. Also, it is desirable to provide


rapid pain relief. We therefore believe that when treating labour pains, the spinal part of CSE should be performed first before inserting the Tuohy needle and epidural catheter. This will provide near instant pain relief, making the subsequent epidural placement a lot easier and safer and without local discomfort. There will be no need for expensive CSE kits that may not always be readily available. By limiting the intrathecal dose, unwanted hypotension can be avoided and we recommend using a single lumbar interspace so that the patient only has one injection of local anaesthetic. This also reduces the extent of spinal ligament bruising and subsequent postdelivery backache. The use of a finebore pencil-point spinal needle almost eliminates the possibility of the epidural catheter passing through the spinal puncture hole [1]. By using low dosages for ‘top ups’ the possibility of a high or total spinal, in the unlikely eventuality of epidural catheter migration into the subarachnoid space, is almost totally eliminated. Our preferred technique for performing CSE in labouring women is to use either the L3–4 or L4–5 interspace. Under aseptic conditions, the chosen interspace is infiltrated with local anaesthetic. Then, with the patient either sitting upright or lying lateral, spinal puncture is performed using a 27 gauge pencil-point (Whitacre) needle, injecting 2.0–2.5 mg of bupivacaine 0.25% plain with 20–25 mg fentanyl. This provides almost immediate relief of labour pains. With the patient more comfortable and co-operative, the epidural catheter is then placed using a 16 gauge Tuohy needle at the same interspace. The catheter is then secured and

flushed with l ml normal saline to prevent any clotting. For extending or prolonging the block, we use 5–12 ml of a mixture of bupivacaine 0.0625– 0.125% and fentanyl 2.5–4 mg.mlÿ1. Therefore, the total dose of bupivacaine with each top-up never exceeds 15 mg, making the possibility of a total spinal extremely unlikely. We have now used this ‘spinal before epidural, single interspace, technique’ in our obstetric practice for well over a year. Our results have been very pleasing with a high degree of patient satisfaction. E. W. S. Cheam L. A. H. Critchley Prince of Wales Hospital, Hong Kong, PRC Reference 1 Rawal N, Van Zundert A, Holmstrom B, Crowhurst JA. Combined spinal– epidural technique. Regional Anesthesia 1997; 22: 406–23.

A cheap ‘glass’ spine

Since the beginning of this century, the flow and spread of local anaesthetics in the cerebrospinal fluid has been illustrated with dyed anaesthetic given into a glass spine filled with Hartmann’s solution. Not long ago, I saw Dr Carrie give a demonstration of this at one of the workshops in the European Society of Regional Anaesthesia. It was simple but very effective. Wishing to be able to show the trainees at our hospital, I have made up a similar piece of equipment using ordinary theatre suction tubing, wired onto a white

509


board, in the correct shape with a paediatric intravenous cannula glued into place. This works just as well as the real ‘glass’ spine and brings the demonstration within the range of the anaesthetic department. It is available for showing to trainees, nurses, medical students and any other people with an interest in the subarachnoid anaesthesia. K. Birkinshaw Queen Margaret Hospital, Dunfermline KY12 0SU, UK Regional anaesthesia – awake or asleep?

We have followed with interest the correspondence regarding the most appropriate time to site an epidural for peri-operative analgesia. A noticeable omission in the ensuing correspondence is that of patient preference. Following a detailed discussion of the advantages, disadvantages and risks associated with intravenous patientcontrolled analgesia (PCA) and patientcontrolled epidural analgesia, seven of our last eight patients elected to have epidural analgesia following upper gastrointestinal surgery. In obtaining informed consent for epidural analgesia, we raised the risks of incomplete analgesia, dural tap with subsequent headache, motor block, residual paraesthesia, injection site tenderness and backache. A frank and open discussion then followed regarding the current debate as to whether the epidural should be sited before or after induction of anaesthesia. The risk of unforeseen nerve damage was raised. Without hesitation, all seven patients elected to have the epidural sited after induction of general anaesthesia. Indeed, one patient stated that if this were not to be the case, he would prefer intravenous PCA. In our experience, given the option, patient preference is to have the epidural sited after the induction of anaesthesia. This adds a further dimension to this ongoing debate. I. H. Shaw I. H. Warnell Newcastle General Hospital,

510

Newcastle upon Tyne NE4 6BE, UK I noted the editorial (Anaesthesia 1998; 53: 727–9) and subsequent correspondence (Anaesthesia 1999; 54: 86–7) on general anaesthesia before or after a regional block. I know of a patient who had a general anaesthetic before a spinal anaesthetic. He was left with serious neurological defects on the right side, a total loss of sensation in his leg, severe pain and penile numbness. An MRI scan revealed a lesion at T11/12 and another at T9. An anaesthetic expert claimed that there was always a very small, residual risk and that, in some unexplained way, the administration of a spinal block could trigger a defect in the central nervous system. If that is accepted, then it will always remain difficult to be sure whether spinal injection under general anaesthetic has added to the risk. I therefore support Professor Wildsmith’s call for caution. The majority of experience has been gained with a ‘block first’ policy. The German guidelines, and their rationale, should be considered here. M. Rosen Cardiff CF2 6SZ, UK I have been most interested in the recent correspondence regarding the widespread international practice of performing regional anaesthetic and analgesic techniques after induction of anaesthesia. I was interested to read of the current situation in Germany as reported by Dr Gruning (Anaesthesia 1999, 54: 86–7) but feel I must ask the question, are there not certain parallels between the current situation in Germany and the situation in the UK after the publication of the Wooley and Roe case [1]? This publication resulted in spinal anaesthesia falling into disrepute and as a result many patients were denied what for them may have been a more appropriate anaesthetic technique on the basis of case report evidence. W. H. Fish Treliske Hospital, Truro TR1 3LJ, UK

Reference 1 Cope RW. The Woolley and Roe case. Anaesthesia 1954; 9: 249–70.

Experts in our field?

I was disappointed (as he was) by Professor Wildsmith’s comment that he was just an anaesthetist (Anaesthesia 1999; 54: 86) in response to the editorial on regional anaesthesia before or after general anaesthesia (Anaesthesia 1998; 53: 727–9). If he isn’t a medical expert in his field, then what hope does our profession and, in particular, the ‘mortal’ anaesthetic body have of being considered a worthwhile speciality by the other medical specialities? Will we ever stand up and be counted as experts in our field? P. W. Doyle West SufFolk Hospital, Bury St Edmunds IP33 2QZ, UK

Failed epidural and the new epidural fixation device

I read with interest the letter by Drs Coupe and Al-Shaikh (Anaesthesia 1999; 54: 98) concerning prevention of epidural catheter migration using a new epidural fixation device, the SIMS Portex 16G Epidural Catheter Clamp (100/339/016). I have also been using the same device for fixation of epidural catheters on the delivery suite, and have found the device easy to use, with no cases of skin irritation or breakdown, no cases of catheter fracture and no evidence of catheter migration. However, I have on a number of occasions been called back to the delivery suite owing to a failed epidural. On inspection of the fixation device, I have found that whilst the epidural catheter was unfractured, it had become ‘wedged’ in the clamp. This resulted in an inability to administer local anaesthetic via the epidural, a distressed and uncomfortable parturient and also required re-siting of the epidural. The epidural fixation device does indeed seem to eliminate movement of the catheter relative to the skin; however,



great care is required when ‘snapping home’ the clamp over the catheter in order to prevent causing an irreversible kink in the catheter and thus a failed epidural. J. E. Bellamy Greenwich District Hospital, London SE10 9HE, UK

The wrong vegetable

The letter from Dr Tuckey (Anaesthesia 1998; 53: 1232) deserves 9/10 for imagination in the use of a potato, but I believe that the wrong vegetable was used. Celery is not only the right shape and size for the flavum, but it also has that gritty feel that you do not get with a potato. I have always taught that the flavum feels like celery. M. Severn Royal Lancaster Infirmary, Lancaster LA1 4RP, UK Too much of a good thing: a faulty Tuohy needle

We would like to report an incident which occurred recently. A 35-year-old primiparous woman, in established spontaneous labour at 4–5 cm cervical dilatation, requested epidural analgesia. After verbal consent had been obtained, and under aseptic conditions, the skin was infiltrated with 8 ml of 1% lignocaine. The patency of the 16-gauge Tuohy needle (Portex Maxipack, SIMS) was checked by passing the epidural catheter, but was not examined more closely. A hole was made in the skin using a trocar needle and the Tuohy needle, with the stylette in place, was inserted. Immediately, resistance was felt and local bruising appeared. The needle was withdrawn and closer inspection revealed that the end of the stylette protruded beyond the end of the Tuohy needle (see figure). A full explanation was given to the patient and, using a new Tuohy needle, satisfactory epidural analgesia was established uneventfully. Any bruising had disappeared 3 days later. This case highlights the importance of inspection of all equipment before use. 䊚 1999 Blackwell Science Ltd

M. H. Alsahaf J. G. Jenkins Royal Surrey County Hospital, Guildford GU2 5XX, UK

A reply from the manufacturer Our investigation into the cause of the incident referred to by Drs Alsahaf and Jenkins concerning our Tuohy needle has been completed. Visual inspection of the needle has confirmed that the stylet protrudes around 2 mm from the tip of the Tuohy needle shaft when fully inserted. It is considered that this has been the result of an isolated manufacturing fault. The locating lug of the stylet had not been positioned correctly in the corresponding recess in the back of the needle hub prior to trimming flush with the needle face. When correctly positioned prior to use, the tip of the stylet then protruded from the needle tip. The length trimming operation referred to is a manual process with the operators using a blade to cut the stylet to length. As a result of a previous incident of this nature, the method used to assemble the components was modified to ensure that the stylet is always fully inserted into the needle prior to trimming. We are confident that this action will effectively prevent any recurrence of this type of incident. Sims Portex Ltd, Hythe, Kent CT2 16JL, UK

Ensuring sterility of opioids for spinal administration

Anaesthetists rigorously ensure asepsis while performing subarachnoid and epidural blocks. Sterilised disposable equipment and sterilised double-wrapped ampoules of local anaesthetics which can be dropped onto spinal trolleys are parts of standard practice. But regarding opioids which may be added to the local anaesthetics, the position is somewhat unsatisfactory. The problem is that the contents of the opioid ampoule are sterile but the outside of the ampoule is not. Many workers draw up the contents with a 5-mm filter needle while an assistant holds the ampoule. Some even use a 0.22-mm Millipore filter for this purpose. These measures may compromise the goal of complete sterility of everything used for central neural blockade and hence become weak links in an otherwise flawless chain of asepsis. As sterilised double-wrapped ampoules of opioids are not readily available commercially, the pharmacy department of our hospital has overcome this problem by making arrangements to have morphine and fentanyl ampoules doublewrapped and sterilised by ethylene oxide. B. G. J. Green G. V. Pathy Neath General Hospital, Neath SA11 2LQ, UK

511


Postpartum femoral neuropathy: more common than you think

We wish to report three cases of postpartum femoral neuropathy, collected over a 6-month period from February 1998 in a UK teaching hospital with 4000 deliveries per annum. Two of the women had received regional anaesthesia for labour and delivery. Case 1 had an uncomplicated vaginal delivery of a 4.23-kg infant in the conventional (semirecumbent) position with epidural analgesia. The following morning, she complained of her right leg giving way when she first rose out of bed. Case 2 had a vacuum extraction of a 3.60-kg infant under epidural analgesia. She was in the lithotomy position for about 90 min. Some 14 h later, when she was allowed out of bed, her right leg gave way and she could not walk. Case 3 had an uncomplicated vaginal delivery of a 4.16-kg infant in the conventional position with transcutaneous electrical nerve stimulation and Entonox for analgesia. On the first postpartum day, she described areas of numbness on both thighs. After neurological examination, case 1 was diagnosed to have right-sided femoral neuropathy and was confirmed on nerve conduction study. Cases 2 and 3 were diagnosed to have bilateral femoral neuropathies. All three patients were discharged home within three postpartum days with minimal sensory deficit and could walk without support. Femoral neuropathy following vaginal delivery can be the result of direct compression of the nerve, proximally within the pelvis by either the fetal head or instruments, or the result of pressureinduced ischaemia at the level of the inguinal ligament when in the lithotomy position. Although not considered a complication of regional anaesthesia, it may present in women who have also had regional anaesthesia. A diagnosis of femoral neuropathy allows regional anaesthesia to be excluded as a direct cause of their postpartum neuropathy [1]. The diagnosis of femoral neuropathy in these cases was made on the basis of a sensory

512

deficit in the distribution of the nerve and absent patellar reflex, with or without the presence of quadriceps weakness. The reduced or absent patellar reflex is the most reliable objective sign in femoral neuropathy [2]. Nerve conduction studies can be used to confirm the diagnosis and demonstrate the site of the lesion. Postpartum femoral neuropathy is associated with a good prognosis and is consistent with a neuropractic injury where axonal loss is less than 50% [3]. Improvement is to be expected within 2–8 weeks and full recovery within 6 months [4]. Once diagnosed, conservative management and reassurance is all that is needed. Femoral neuropathy following vaginal delivery is currently considered rare. Around 1900, it complicated 3.2% of vaginal deliveries [5]. In 1990, Vargo et al. reported an incidence of 2.8 per 100 000 cases and described it as a relic of an earlier era [6]. The incidence in our series is 1.5 per 1000 and is similar to that of Al Hakim and Katirji who reported an incidence of 1.1 per 1000 in 1993 [7]. We conclude as they did that the condition is currently underreported. Obstetric anaesthetists should be aware of this when asked to assess women with postnatal neuropathy. A. Q. Dar A. Robinson G. Lyons St James’s University Hospital, Leeds LS9 7TF, UK References 1 Russel IF. Postpartum neurological problems. In: Russel IF, Lyons G, eds. Clinical Problems in Obstetric Anaesthesia, 1st edn. London: Chapman & Hall, 1997; 147. 2 Hopper CL, Baker JB. Bilateral femoral neuropathy complicating vaginal hysterectomy. Obstetrics and Gynaecology 1968; 32: 543–7. 3 Kuntzer T, Melle GV, Regli F. Clinical and prognostic features in unilateral femoral neuropathies. Muscle and Nerve 1997; 20: 205–11. 4 Donaldson JO, Wirz D, Mashman J. Bilateral postpartum femoral neuropathy. Connecticut Medicine 1985; 49: 496–8.

5 Donaldson JO. Maternal obstetric palsies. In: Neurology of Pregnancy, 2nd edn. London: W.B. Saunders, 1989; 45–6. 6 Vargo MM, Robinson LR, Nicholas JJ, Rulin MC. Postpartum femoral neuropathy: relic of an earlier era? Archives of Physical Medicine and Rehabilitation 1990; 71: 591. 7 Hakim MA, Katirji MB. Femoral mononeuropathy induced by the lithotomy position. A report of 5 cases with a review of literature. Muscle and Nerve 1993; 16: 891–5.

A machinery murmur

A 55-year-old man presented for cystoscopy and bladder neck procedure. Apart from urinary frequency and urgency, he was fit and took no medication. His admission blood pressure was 105/70 mmHg. After induction with alfentanil 500 mg and propofol 220 mg, I inserted a size 4 LMA and maintained anaesthesia with the patient spontaneously breathing nitrous oxide/oxygen and isoflurane 1%. Following cystoscopy, the surgeon decided to perform a limited TURP. There was minimal blood loss. Despite 1500 ml crystalloid and 10 mg ephedrine, the patient’s blood pressure, measured on his right arm by automatic oscillotonometer, remained persistently between 75 and 80 mmHg systolic. A second blood pressure cuff was put on his left arm and measurements alternated using the same oscillotonometer. Left arm systolic blood pressure readings were consistently 25 mmHg higher. Asymmetry of blood pressure readings during routine anaesthesia has been reported previously from this hospital [1]. To ascertain whether the variation was associated with any vascular pathology, I listened to the patient’s neck and precordium. Chest ausculation was normal and there were no orbital bruits, but I was amazed to hear a continuous loud buzzing noise, similar to a 50-Hz electrical hum, audible over the front and both sides of the neck between the mastoid processes and the clavicles. The noise did not vary with circulation



or respiration. Several clinicians confirmed its presence. While trying to discover its cause, we temporarily switched off, in succession: the diathermy equipment, the electric warming mattress, the ECG and, finally, the electrical supply to the Ohmeda Modulus CD anaesthetic machine. Only the last of these caused the hum to cease. There were no electrical connections between our version of the Modulus CD and the patient. Further investigation showed that the sound came from the capnograph pump, which was unusually noisy. In a Modulus anaesthetic machine the waste gas from the capnograph is returned to the top of the soda lime absorber. The sound from the noisy pump was transmitted along this waste pipe and back up the expiratory limb of the circle system, eventually to be transmitted through the LMA cuff and so be audible externally. The patient made an uneventful recovery and postoperatively had no asymmetry of blood pressure measurements or vascular bruits. Once the anaesthetist’s attention had been drawn to the noise from the capnograph, it remained to irritate him for the rest of the operating list. C. J. H. Johnson Southmead Hospital, Bristol BS10 5NB, UK Reference 1 Gilmore KJ, Goodman NW. Unequal blood pressure recordings in the arms. Anaesthesia 1998; 53: 1135.

Central venous access – a problem with a peripheral approach

Insertion of a central venous line by any route has its attendant complications. The antecubital route to the central venous circulation is widely regarded as being safer than other vascular access sites for short-term monitoring. Noncentral localisation of the catheter tip, however, is a common problem especially when using the cephalic vein [1]. Problems can arise though as with an attempted insertion of a ‘drum’ catheter into a central vein via a peripheral vein 䊚 1999 Blackwell Science Ltd

in the antecubital fossa. The catheter was advanced without undue force but, when adequate length was considered to have been inserted, it was found impossible to remove the central guide wire. On examination, the catheter had advanced to the level of just below the humoral head where it had met some resistance. Further advancement of the catheter caused it to exit through the vein wall and form a knot which had to be removed surgically (Fig. 1). C. M. Timberlake King’s College Hospital, London SE5 9RS, UK Reference 1 Webre DR, Arens JF. Use of cephalic and basilic veins for introduction of central venous catheters. Anesthesiology 1973; 38: 389–92.

Underwired bras and the MRI scanner

In reply to Dr Taylor’s letter (Anaesthesia 1998; 53: 1237), he may rest assured that steel alloy underwired bras do not cause a problem in the MRI scanner. This does not, however, stop the radiographers and ODAs attempting to persuade naı¨ve young nurses and SHOs to remove their bras prior to MRI scanning. As far as I am aware they have not yet succeeded!

J. E. Bellamy Greenwich District Hospital, London SE10 9HE, UK

The Heisenberg uncertainty principle and anaesthetic performance

One of the implications of quantum theory is that it is impossible to know with arbitrary accuracy both the position and momentum of a photon – the limitation of the accuracy in question being given by Planck’s constant/2p. When a photon is observed to try to ascertain its position, the act of viewing changes that which is being viewed. Whilst attending a course at an anaesthetic simulator, I noted an analogous example of this phenomenon. While ‘pre-oxygenating’ a simulated patient prior to a rapid sequence induction, one anaesthetist used a mixture of 50 : 50 nitrous oxide and oxygen, and the following anaesthetist used no fresh gas flow at all. Both doctors participating were experienced consultants, and whilst both of these mistakes are made in the real world, the anticipation of the expected emergency scenario altered their usual practice. As anaesthetic simulators continue to increase in sophistication, their use may become more prevalent in undergraduate and postgraduate training. At least in 513


their current pattern of use, the problem remains that the frequency of occurrence of (simulated) critical incidents will always be greatly higher than that seen in real life practice, and that the subjects’ behaviour and performance will be modified accordingly. As with photons, observation alters the properties of the

observed. It is interesting to note that in this regard at least, the behaviour of anaesthetists can be modelled on that of subatomic particles. M. Williams Queen Alexandra Hospital,

Portsmouth PO6 3LY, UK

Reference 1 Heisenberg W. The Physical Principles of the Quantum Theory. New York: Dover, 1930.

Deaths of members reported to Council

Cooper, Joan. MRCS, LRCP, DA, FFARCS. Trained first as a pharmacist and later studied medicine at Charing Cross Hospital, qualifying in 1920. She became a general practitioner in Cambridge and Honorary Anaesthetist at Addenbrooke’s Hospital. After the Second World War, she became a full-time anaesthetist and was appointed a consultant at Addenbrooke’s Hospital following the introduction of the NHS in 1948. Died at the age of 106. Lewis, Edward Brian KStJ. MA (Camb), MB, BChir, FFARCS. Past member of the Council of the Association (1973–76) and Vice President (1986–88). Member of Council of the British Medical Association and Deputy Chairman of CCHMS. Member of General Medical Council. Marshall, Merlin. MB, BCh (Cambs), FFARCS. Formerly consultant anaesthetist, Newcastle. O’Driscoll, M. Cork. Retired member. Perks, Eustace Robert. MB, BCh (Birm), FFARCS. Formerly consultant anaesthetist, Sheffield and surgeon lieutenant RNVR.

514
