What does it take to start an oropharyngeal fire? Oxygen requirements to start fires in the operating room

IntroductionAirway fires are a well-described and potentially devastating complication of oropharyngeal surgery. However, the actual factors required to ignite the fire have never been well-delineated in the medical literature. In this study, we used a mechanical model to assess the oxygen parameters necessary to cause an oropharyngeal fire.MethodsAn electrosurgical unit (Bovie) was grounded to a whole raw chicken and a 6.0 endotracheal tube (ETT) was inserted into the cranial end of the degutted central cavity. Oxygen (O2) was then titrated through the ETT tube at varying concentrations, with flow rates varying from 10 to 15 L/min. Electrocautery (at a setting of 15 W) was performed on tissue in the central cavity of the chicken near the ETT. All trials were repeated twice to ensure accuracy. Positive test results were quantified by the time required to obtain ignition of any part of the mechanical setup and time required to produce a sustained flame. A test was considered negative if no ignition could be obtained after four minutes of direct electrocautery.ResultsAt an O2 concentration of 100% and a flow rate of 15 L/min, ignition with a sustained flame was obtained between 15 and 30 s after initiation of electrocautery. At 100% O2 at 10 L/min, ignition was obtained at 70 s with immediate sustained flame. At an O2 concentration of 60%, ignition occurred at 25 s and sustained fire after 60 s. At an O2 concentration of 50% ignition with a sustained flame occurred between 128 and 184 s. At an O2 concentration of 45%, neither ignition nor sustained flames could be obtained in any trial.ConclusionsOperating room fires remain a genuine danger when performing oropharyngeal surgery where electrocautery is performed in an oxygen-enriched environment. In our study, higher O2 flow rates with higher FiO2 correlated with quicker ignition in the chicken cavity. A fire was easily obtained when using 100% O2; as the O2 concentration decreases, longer exposure to electrocautery is required for ignition. Below 50% O2 we were unable to obtain ignition. Our study is the first to examine the relative risk of ignition and sustained fire in a mechanical model of oropharyngeal surgery. Decreasing the fraction of inspired O2 (FiO2) to less than 50% may substantially decrease the risk of airway fire during oropharyngeal surgery.