Patients Ventilated Humidification in Mechanically ...

A Randomized Clinical Trial Comparing an Extended-Use Hygroscopic Condenser Humidifier With Heated-Water Humidification in Mechanically Ventilated Patients Marin H. Kollef, Steven D. Shapiro, Vanessa Boyd, Patricia Silver, Benjamin Von Harz, Ellen Trovillion and Donna Prentice Chest 1998;113;759-767 DOI 10.1378/chest.113.3.759 The online version of this article, along with updated information and services can be found online on the World Wide Web at: http://chestjournal.chestpubs.org/content/113/3/759

Chest is the official journal of the American College of Chest Physicians. It has been published monthly since 1935. Copyright1998by the American College of Chest Physicians, 3300 Dundee Road, Northbrook, IL 60062. All rights reserved. No part of this article or PDF may be reproduced or distributed without the prior written permission of the copyright holder. (http://chestjournal.chestpubs.org/site/misc/reprints.xhtml) ISSN:0012-3692

Downloaded from chestjournal.chestpubs.org by guest on July 24, 2011 1998 by the American College of Chest Physicians

A Randomized Clinical Trial Comparing an Extended-Use Hygroscopic Condenser Humidifier With Heated-Water Humidification in Mechanically Ventilated Patients* Marin H. Kollef, MD, FCCP; Steven D. Shapiro, MD, FCCP; Vanessa Boyd, RRT; Patricia Silver, ME; Benjamin Von Harz, Ellen Trovillion, BSN; and Donna Prentice, MSN

RRT;

Study objective: To determine the safety and cost-effectiveness of mechanical ventilation with an extended-use hygroscopic condenser humidifier (Duration; Nellcor Puritan-Bennett; Eden Prairie, Minn) ventilation with heated-water humidification. compared with mechanical randomized clinical trial. Design: Prospective Setting: Medical and surgical ICUs of Barnes-Jewish Hospital, St. Louis, a university-affiliated teaching hospital.

undergoing

mechanical ventilation. Patients: Three hundred ten consecutive qualified patients Interventions: Patients requiring mechanical ventilation were randomly assigned to receive humidification with either an extended-use hygroscopic condenser humidifier (for up to the first 7 days of mechanical

ventilation) or heated-water humidification.

Measurements: Occurrence of ventilator-associated pneumonia, endotracheal tube occlusion, duration of mechanical ventilation, lengths of intensive care and nospitalization, acquired multiorgan dysfunction, and

hospital mortality.

Results: One hundred sixty-three patients were randomly assigned to receive humidification with an extendeduse hygroscopic condenser humidifier, and 147 patients were randomly assigned to receive heated-water humidmcation. The two groups were similar at the time of randomization with regard to demographic characteristics, ICU admission diagnoses, and severity of illness. Risk factors for the development of ventilatorassociated pneumonia were also similar during the study period for both treatment groups. Ventilatorassociated pneumonia was seen in 15 (9.2%) patients receiving humidification with an extended-use hygroscopic condenser liumidifier and in 15 (10.2%) patients receiving heated-water humidification (relative risk, 0.90; 95% confidence interval=0.46 to 1.78; p=0.766). No statistically significant differences for hospital mortality, duration of mechanical ventilation, lengths of stay in the hospital or ICU, or acquired organ system derange¬ ments were found between the two treatment groups. No episode of endotracheal tube occlusion occurred in either treatment group. The total cost of providing humidification was $2,605 for during the study period a hygroscopic condenser humidifier compared with $5,625 for patients receiving heatedreceiving patients water humidification. Conclusion: Our findings suggest that the initial application of an extended-use hygroscopic condenser humidifier is a safe and more cost-effective method of providing humidification to patients requiring mechanical ventilation compared with heated-water humidification. (CHEST 1998; 113:759-67)

Key words: airway humidification; intensive care; mechanical ventilation; outcomes; ventilator-associated pneumonia Abbreviations: APACHE=acute physiology and chronic health evaluation; CI=confidence interval; HCH=4iygroscopic con¬ denser humidifier; HCHF=HCH with bacteria-filtering properties; HME=heat and moisture exchanger; HMEF=HME with bacteria-filtering properties; PaO^Ic^.ratio of arterial blood oxygen tension to the concentration of inspired oxygen

TT umidification of inspiratory gases is widely accepted to be an essential practice for patients receiving mechanical ventilation through an endotra-*--*.

*From the

of Medicine, Pulmonary and Critical Department (Drs. Kollef and Shapiro), Washington University School of Medicine, and Departments of Respiratory Therapy (Mss. Boyd and Silver, and Mr. Von Harz), Nursing (Ms. Trovillion), and Infection Control (Ms. Prentice), Barnes-Jewish Hospital, St. Louis. This research was in Care Division

supported part by an educational grant from Nellcor Puritan-Bennett. Manuscript received May 30, 1997; revision accepted August 25. Reprint requests: Marin H. Kollef, MD, FCCP, Pulmonary and Critical Care Division, Washington University School of Medi¬ cine, Rox 8052, 660 S Euclid Ave, St. Louis, MO 63110

cheal tube or tracheostomy tube.12 Many properties and functions of the respiratory tract, including lung mechanics, surfactant production, gas exchange, and mucociliary clearance can be adversely affected by the continuous loss of heat and moisture during ventilatory support.35 To avoid these potentially serious complications, heated-water humidification systems have been traditionally employed as the primary means of providing humidified and heated inspiratory gases to mechanically ventilated pa¬ tients.6

Modern high-flow heated-water humidifiers are capable of providing a relative humidity of nearly

CHEST / 113 / 3 / MARCH, 1998 Downloaded from chestjournal.chestpubs.org by guest on July 24, 2011 1998 by the American College of Chest Physicians

759

100% to inspiratory gases at temperatures near body

temperature.6 However, these humidification sys¬ tems also have disadvantages that include their high maintenance costs, the production of circuit tubing condensate (ie, overhumidification) that can serve as a source of lung infection, increased work loads for patient care providers, mechanical malfunction of the humidification apparatus, and overheating of the inspired gases.6-8 Additionally, improper tempera¬ ture or humidification settings can produce inade¬ quate humidification of the inspiratory gases result¬ ing in potentially life-threatening complications to patients (eg, endotracheal or tracheostomy tube occlusion).9 In an attempt to simplify the care of ventilated patients, and to avoid the mechanically with the use of heated-water associated problems humidification systems, artificial noses or heat and moisture exchangers (HMEs) have been developed to conserve both patient heat and the water content of the airway gases.10'11 to heated-water

HMEs are attractive alternatives humidification systems because of their passive op¬ eration (ie, they do not require electricity or active low cost. HMEs have heating elements) and their been employed primarily for short-term use in me¬ ventilated patients, including during trans¬ chanically out portation of the ICU and during anesthesia for operative procedures.12 Hygroscopic condenser hu¬ midifiers (HCHs) are similar to HMEs but work by expired heat and moisture in collecting the patient's a hygroscopically treated insert (ie, surfaced by lithium chloride or calcium chloride) that chemically improves heat and moisture exchange.1213 If either an HCH or HME possesses bacteria-filtering prop¬ erties, it can be designated as an HCHF or HMEF.13 Several reports have suggested that HMEs and HCHs can also be safely used in patients requiring more prolonged mechanical ventilation.1415 Addi¬ investigation found that the same tionally, one recent HME could be employed for up to 48 h without increasing a patient's risk for ventilator-associated pneumonia or other adverse outcomes.16 However, should water, airway secretions, or blood get into these devices, resistance to airflow and patient work of breathing can increase.13 Therefore, they should be changed anytime liquid contamination is sus¬ Finally, the clinical application of HMEs and pected. HCHs appears to provide safe levels of humidifica¬ tion to patients requiring mechanical ventilation while also reducing the occurrence of ventilator circuit bacterial colonization.121317 To better determine the optimal use of HCH in the ICU, we performed a randomized clinical trial comparing the safety and cost-effectiveness of me¬ chanical ventilation with humidification provided by either a heated-water system or an extended-use 760

HCH. We hypothesized that extending the use of an HCH beyond 24 h would be safe based on the

available clinical data.16 The main

objectives of our

investigation were to determine (1) the incidence of ventilator-associated pneumonia and clinical out¬ comes of patients receiving an extended-use HCH and (2) to compare these outcomes with patients receiving heated-water humidification. Materials

and

Methods

Study Location and Patients The study was conducted at a university-affiliated teaching hospital: Barnes-Jewish Hospital (900 beds). During a 4-month period (October 1996 to January 1997), all patients receiving mechanical ventilation in the medical and surgical ICUs of this hospital were potentially eligible for this investigation. Patients were entered into the investigation if they were older than 17 years and required mechanical ventilation while in the ICU setting. Patients were excluded if they had transferred from other hospitals and had already received mechanical ventilation, if they had heart or lung transplantation, or if they had massive hemop¬ tysis. The study was approved by the Washington University School of Medicine Human Studies Committee. The require¬ ment for informed consent was waived because this study was a quality assessment of two low-risk practices already in clinical Study Design Patients were randomly assigned to receive humidification with an extended-use HCH (Duration; Nellcor Puritan-

either

or heated-water humidification. done using opaque, sealed envelopes that were opened at the time each patient was enrolled in the study. For purposes of this investigation, ventilator circuits were defined to include the gas delivery tubing, in-line suction cathe¬ ters, humidifier water reservoirs or HCHs, water traps, and medication delivery devices (such as metered-dose inhaler cham¬ bers or adapters). Starting at the patient's endotracheal tube, in-line suction catheters were attached followed by a medication delivery device (if used), an HCH (if used), and the gas7 delivery for the first days of tubing. HCHs could bein used onlyrandomized to this group. mechanical ventilation patients After 7 days of mechanical ventilation, patients were switched to heated-water humidification. Based on published experience, the same ventilator circuit tubing and in-line suction catheter were used throughout each patient's course of mechanical ventilation unless they became visibly soiled or experienced a mechanical failure.1821 HCHs were not removed during the administration of bronchodilators since they were located further away from the patient relative to the medication delivery device. Respiratory therapists examined all patients and ventilators at least every 2 h.

Bennett; Eden Prairie, Minn) Randomization

was

During these rounds, patient-ventilator interaction was exam¬ ined, the ventilator circuit was checked for condensate accumu¬ lation or air leaks, the in-line suction catheter was inspected, and the overall function of the ventilator was reviewed. Any identified

condensate in the ventilator tubing or water traps was disposed of during these rounds in fluid collection containers available in each patient's room. Additionally, the patency of the patient's endotracheal tube or tracheostomy tube was checked at least every 8 h by passing a suction catheter through the artificial

airway.

Clinical Downloaded from chestjournal.chestpubs.org by guest on July 24, 2011 1998 by the American College of Chest Physicians

Investigations in Critical Care

The ventilators used for this

study included

the

following:

Siemens Servo 900C (Siemens-Elema Ventilator Systems; Schaumburg, 111); Puritan-Bennett 7200 Series (Puritan-Bennett Corp; Carlsbad, Calif); and Bird 8400 Series ventilators (Bird Products Corp; Palm Springs, Calif). We employed an extendeduse HCH (Duration; Nellcor Puritan-Bennett) that has been

demonstrated to maintain its humidification properties

in

a

test

lung system for 7 days of use without deterioration (inspired humidity, 30 mg/L; resistance, 1.6 cm H20/L/s at a flow rate of 60 L/min; dead space, 90 mL). We employed standard gas (Hudson RCI Ventilator Set; Hudson RCI; delivery tubing for Temecula, Calif) patients receiving an HCH and heated-wire gas delivery tubing (Isothermal Breathing Circuit; Baxter Health¬ care Corp; Deerfield, 111) for patients receiving heated-water humidification (MR730 Respiratory Humidifier; Fisher & Paykel Healthcare; Auckland, New Zealand). Patients switched from an HCH to heated humidification also had their ventilator tubing changed. The heated-water humidification system was set to deliver a temperature of 35° to 36°C and 100% relative humidity at the proximal airway. These humidification settings were selected to avoid airway obstruction due to the delivery of inadequate relative humidity.9 Aerosolized medications were delivered to patients using metered-dose inhalers and an at¬ tached chamber device (Aerovent; Monaghan Medical Corp; Plattsburg, NY). Water traps (Marquest Medical Products Inc; Englewood, Colo) were used in ventilator circuits when signifi¬ cant condensate formation was noted. Data Collection For all

study patients, the following characteristics were re¬ prospectively by one of the investigators: age, gender, diagnosis at hospital admission, indication for mechanical venti¬ lation, premorbid lifestyle score,22 the ratio of arterial blood oxygen tension to the concentration of inspired oxygen (Pa02/ FIo2), and severity of illness based on APACHE II (acute and chronic health evaluation) scores.23 Specific pro¬ physiology cesses of medical care examined to corded

assess risk factors for ventilator-associated pneumonia were the administration of ant¬

acids or histamine2-receptor antagonists, supine positioning of the head of the bed, pharmacologic aerosol treatments during mechanical ventilation (such as bronchodilators, antibiotics, mucolytics), occurrence of a witnessed aspiration event, administra¬ tion of antibiotics during the same hospitalization but prior to intubation and the start of mechanical ventilation, fiberoptic reintubation, surgical tracheostomy, and transport bronchoscopy, out of the ICU during mechanical ventilation. Additionally, the specific indication for changing an extended-use HCH or switch¬ ing to heated-water humidification (eg, scheduled according to the study protocol, soil, mechanical defect, or excessive airway secretions) was also recorded prospectively. One of the investigators made daily rounds on all study patients in the ICUs to identify eligible patients. Patients entered into the study were prospectively followed up for the occurrence of ventilator-associated pneumonia until they were successfully weaned from mechanical ventilation, were discharged from the hospital, or died. All patients suspected of having ventilatorassociated pneumonia were prospectively and independently reviewed by another investigator (an infection control nurse) who was blinded to patients' treatment group assignments. The diagnosis of ventilator-associated pneumonia was strictly based on the predetermined criteria described below. In addition to the occurrence of ventilator-associated pneumo¬ nia, we assessed secondary outcomes, including the lengths of hospitalization and intensive care, the duration of mechanical ventilation, the number of acquired organ system derangements using the organ system failure index,24 endotracheal tube occlu¬

sions, hospital mortality, and mortality ventilator-associated pneumonia.

directly

attributed

to

Definitions All definitions were selected prospectively as part of the original study design. The premorbid lifestyle score was used as previously defined:22 zero indicated that the patient was em¬ ployed without restriction; 1 indicated that the patient was independent, fully ambulatory, not employed, or employed with 2 indicated that the had

restriction; patient restricted activities, could live alone and get out of the house to do basic necessities, or had severely limited exercise ability; 3 indicated that the patient was housebound, could not get out of the house unas¬ sisted, could not live alone, or could not do heavy chores; and 4 indicated that the patient was bed- or chairbound. We calculated APACHE II scores on the basis of clinical data available from the first 24-h period of intensive care.23 The organ system failure index was modified from that used by Rubin and coworkers.24 One point was given for acquired dysfunction of each organ system: renal dysfunction, a twofold increase in baseline creatinine level or an absolute increase in baseline creatinine level of 176.8 (xmol/L (2.0 mg/dL); hepatic dysfunction, an increase in total bilirubin level to >34.2 ixmol/L (2.0 mg/dL); pulmonary dysfunction was defined as (1) a require¬ ment for mechanical ventilation for a diagnosis of pneumonia, COPD, asthma, or pulmonary edema (cardiogenic or noncardiogenic); (2) a Pa02 of 0.50; or (3) the use of at least 10 cm H20 of positive end-expiratory pressure; hematologic dysfunction, the presence of disseminated intravascular coagulation, a leukocyte count of 48 h after the start of mechanical ventilation or within 48 h of extubation. Persistence of the infiltrate was established if it was radiographically visible for at least 72 h. Fever was defined as an increase in the core temperature of 1°C or more and a core temperature of more than 38.3°C. Leukocytosis was defined as a 25% increase in circulating from baseline and a leukocyte count of >10X103/ leukocytes mm3 (10X109/L). Tracheal aspirates were considered purulent if a Gram's stain showed >25 neutrophils per high-power field. Hospital mortality was defined as those patient deaths occur¬ ring during the study hospitalization. Mortality directly related to

CHEST / 113 / 3 / MARCH, 1998 Downloaded from chestjournal.chestpubs.org by guest on July 24, 2011 1998 by the American College of Chest Physicians

761

stepwise approach was used to enter new terms into the logistic regression model; 0.05 was set as the limit for the

ventilator-associated pneumonia was predetermined to be present when a patient died during an episode of nosocomial pneumonia and the death could not be directly attributed to any

A

acceptance or removal of these terms. All potential confounding variables associated with ventilator-associated pneumonia were forced to enter the model regardless of statistical significance. Results of the logistic regression analysis are reported as adjusted odds ratios with 95% confidence intervals (CIs). Relative risks and their 95% CIs were calculated using standard methods. Values are expressed as the mean±SD (continuous variables) or as a percentage of the group from which they were derived (categorical variables). All p values were two tailed, and p values of