BRITISH JOURNAL OF ANAESTHESIA drill which simulates the difficult case is needed. The incidence of failed intubation in obstetrics is quoted widely as 1 in ...
BRITISH JOURNAL OF ANAESTHESIA
502 drill which simulates the difficult case is needed. The incidence of failed intubation in obstetrics is quoted widely as 1 in 300; our current figure is 1 in 800, which suggests that the simple expedient of practising the Macintosh method may produce a valuable improvement. Maternal deaths associated with difficult intubation are bound to raise questions in court about the training of junior staff—those responsible for training could be subpoenaed. An Army commander who sent troops into action undrilled would have some difficult questions to answer I R. R. CORMACK F. CARU K. N. WILLIAMS London REFERENCES 1. DHSS. Report on Confidential Enquiries into Maternal Deaths in England and Wales in 1979-1981. London:
HMSO, 1986; 86-87. 2. Bellhouse CP, Dore C. Criteria for estimating likelihood of difficulty of endotrachcal intubation with the Macintosh laryngoscope. Anaesthesia and Intensive Care 1988; 16:
329-337. 3. Oates JDL, MacLeod AD, Oates PD, Pearsall FJ, Howie JC, Murray GD. Comparison of two methods for predicting difficult intubation. British Journal of Anaesthesia 1991; 66: 305-309.
DESATURATION DURING TOTAL KNEE REPLACEMENT Sir,—Since publishing my previous work [1], I have encountered two cases of desaturation in patients, aged 67 and 71 yr, undergoing total knee replacement under general anaesthesia. Premedication consisted of papaveretum 10 mg with hyoscine 0.2 mg. Anaesthesia was induced with thiopentone 300 mg and trachea] intubation was facilitated by vecuronium 6 mg. The lungs were ventilated mechanically and anaesthesia was maintained with 66 % nitrous oxide and 1 % enflurane in oxygen. Both patients were in the supine position. The arterial pressure, oxygen saturation and inspired oxygen concentration were monitored non-invasively (Cardiocap, Datex). The oximeter probe was positioned on the ear. Both patients were healthy and non-smokers, and both demonstrated a decrease in saturation, of 3 % and 5 % respectively, which occurred 1 min after insertion of cement for the femoral components. The episodes of desaturation lasted for 5 and 7 min, respectively, with no accompanying changes in arterial pressure or heart rate. There were no other episodes of desaturation during the procedures. Both patients had a tourniquet around the thigh at pressures of 175-200 mm Hg greater than the systolic arterial pressure. The prostheses used were of the short-stemmed Kinnamax variety. Desaturation during cemented total knee replacement has been reported [2]. It has been suggested that pulmonary changes were more common with use of the long-stemmed total knee prostheses than with the short-stemmed, because of the relatively large intramedullary cavities and the larger amount of cement required. It is possible that emboli (fat, cement, air or marrow) are forced into the systemic circulation through the intramedullary vessels as the cement sets—a
process that results in increased intramedullary pressures [3]. This may explain the occurrence of systemic emboli despite the use of tourniquets. As it has been shown that use of an FlOt of 0.5 significantly reduces the incidence of desaturation in total hip replacement, the same recommendation should apply to total knee replacement. B. AL-SHADCH
London REFERENCES 1. Al-Shaikh B. Effect of inspired oxygen concentration on the incidence of desaturation in patients undergoing total hip replacement. British Journal of Anaesthesia 1991; 66:
580-582. 2. Byrick RJ, Forbes D, Waddell JP. A monitored cardiovascular collapse during cemented total knee replacement. Anesthesiology 1986; 65: 213-216. 3. Kallos T, Enis JE, Gollan F, Davis JH. Intramedullary pressure and pulmonary embolism of femoral medullary contents in dogs during the insertion of bone cement and prosthesis. Journal of Bone and Joint Surgery 1974; 56:
1363-1367.
ATRACURIUM AND SUXAMETHONIUM Sir,—We read with great interest the paper by Donati and colleagues [1] in which the pharmacokinetic and pharmacodynamic components of the change in dose response to atracurium after previous exposure to suxamethonium were elegantly elucidated. The paper adds strong evidence of a significantly increased sensitivity of the neuromuscular junction to non-depolarizing neuromuscular blocking agents after previous exposure to suxamethonium. We would like to point out a small error (obviously a slip of the pen), which initially caused us some confusion. In the first paragraph of the introduction the sentence "A shift to the right of the dose—response curve to vecuronium [3] has been described with previous exposure to suxamethonium " should read "A shift to the left...". N. J FAUVEL S. A. FELDMAN
London REFERENCE 1. Donati F, Gill SS, Bevan DR, Ducharme J, Theoret Y, Varin F. Pharmacokinetics and pharmacodynamics of atracurium with and without previous suxamethonium administration. British Journal of Anaesthesia 1991; 66:
557-561. Sir,—Thank you for the opportunity to respond to Drs Fauvel and Feldman, who should be congratulated for their careful reading of our report. They are, of course, correct in suggesting that we should have said " A shift to the left...". We hope they will accept our apologies for this unfortunate "slip of the pen...". F. DONATI Montreal
