TITLE: EFFECTIVENESS OF A PLASTIC BAG IN PREVENTING HEAT LOSS: A BENCH MODEL

AUTHORS: Lawrence J. Caruso, MD, Stephen Mnookin, MD, A J. Layon, MD
AFFILIATION: University of Florida, Gainesville, FL.

INTRODUCTION: Intraoperative hypothermia has been shown to increase perioperative morbidity in select patients (1). Several methods of heat preservation are effective, including forced air warmers, fluid warmers, and raising room temperature. Placing a plastic bag over the patient's head is also used but has not been studied. We used a bench model to evaluate the effectiveness of a plastic bag in preventing heat loss to the environment.
METHODS: A liter bag of warmed saline simulated a patient's head. 10 bags were pre-warmed to 38°C and placed on a bed in the OR with the thermostat set at 25°C. Five bags were covered with a clear plastic bag. The other 5 bags of saline were left exposed. "Intrabag" temperature measurement of each bag of saline was recorded every 15 min for 2 hrs, using an inserted probe. After transformation to ranked data, experimental results were analyzed using two way repeated measures ANOVA (SigmaStat for Windows, V. 2.03, SPSS Inc. 1977). Alpha was set at 0.05 for statistical significance.
RESULTS: Five sets of data were analyzed for each condition (covered versus exposed). Ambient temperature averaged 23.8°C. The initial fluid temperature in both groups was similar. Both covered and uncovered bags lost heat over time. However, by 30 minutes the covered, as compared to the exposed, group remained significantly warmer. This difference was maintained to 120 minutes of study (Fig. 1).
CONCLUSION: The use of a clear plastic cover retards heat loss in a bench model. While there are limitations to using this model to simulate a patient's head, covering the head with a plastic bag may provide a simple, safe, and inexpensive technique to supplement or replace more expensive methods of heat conservation.
REFERENCES:

(1) JAMA 1997;277:1127-1134.