Abstract
S201 Operating room fires continue to occur, the most serious of which are airway fires. Work has been done examining the oxygen index of flammability of various endotracheal tube (ETT) materials in an oxygen and nitrous oxide enriched atmosphere [1]. Our goal was to determine the effect that volatile anesthetics have upon the oxygen index of polyvinylchloride (PVC) and red rubber (RR), two common ETT materials. We postulate that due to the similar chemical structures of halogenated anesthetics and halogenated fire extinguishing agents (halons), volatile anesthetics might reduce the flammability of ETT materials. METHODS: The measurement of oxygen index was based upon the American Society for Testing and Materials (ASTM) standards for determining the minimum oxygen concentration to support candle-like combustion of plastics. Nitrogen and oxygen gases were obtained from commercial cylinders and were of medical grade. The gases were routed through flowmeters then to an agent specific anesthetic vaporizer. From the vaporizer, the gases entered a mixing chamber and then flowed upward through a cylindrical test chamber. Midway in the test chamber was a clamp in which the ETT material was placed. The atmosphere within the test chamber was then controlled by varying the oxygen and nitrogen flows and adjusting the agent specific vaporizer. Steady state concentrations were confirmed with an Ohmeda RGM multigas analyzer and an oxygen analyzer. The material was then ignited with a methane pilot flame. While maintaining a constant anesthetic agent concentration the oxygen concentration was adjusted to determine the minimum O2 concentration which would support sustained combustion. Halothane, isoflurane, and desflurane were each studied at four different concentrations ranging from low to maximum vaporizer output. RESULTS: Our results, represented below, indicate that the O2 indices of both PVC and RR are increased in the presence of halogenated anesthetics. Halothane, structurally most similar to halon fire extinguishing agents, has the most pronounced effect upon the O2 index but when compared on and equi-MAC basis is similar to Desflurane. Isoflurane appears to be least effective when examined within its clinical range. (Figure 1)Figure 1It appears from our data that the use of halogenated anesthetics may be instrumental in minimizing the risk of airway fire since they increase the oxygen concentration necessary to support the combustion of the most common ETT materials. However, in spite of this data, it is premature to recommend their use clinically since the toxicity of the pyrolysis and combustion products of these agents is yet to be determined.
Published Version
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