Background The anesthesiology standard of care requires limiting oxygen (O2) concentration to less than or equal to 30% during monitored anesthetic care for upper chest and head and neck surgery to reduce the fire risk. While Venturi devices are used to regulate O2 concentration, they generate high flow rates, which may increase O2 concentration near the face mask. Even small increases of O2 concentration greater than room air significantly increase combustibility, highlighting the need for careful O2 delivery strategies. Methods A face mask was attached to a full-body patient simulator. The mask was connected to 1) the breathing circuit via a 15-mm tracheal tube adapter using the anesthesia machine's O2 blender set at 30%, or 2) the auxiliary O2 port using a 31% Venturi device. Surgical drapes were placed on intravenous poles ("ether screen") to separate the anesthesia and surgical side. Inflow O2 flow was 6 L/min for both groups, with the Venturi delivering ≈52 L/min. After room air calibration, ambient O2 concentrations were measured at three sites on the anesthesia side and three on the surgical side of the drape at no flow and then 15, 30, and 60 minutes after O2 flow initiation. Experiments were repeated three times. Results The pooled differences in the O2 concentration increases between the two devices were 0.80% (95% CI 0.53 to 1.07, P<.001) on the surgical side and 2.22% (95% CI 2.02 to 2.42, P<.001) on the anesthesia side of the ether screen. At 60 minutes, the mean (SD) concentrations in the Venturi group were 22.99% (0.31%) on the anesthesia side and 21.72% (0.90%) on the surgical side. Corresponding values in the anesthesia circuit group were 21.07% (0.12%) and 21.00% (0.11%). Conclusions A 31% Venturi device resulted in clinically relevant increases in ambient O2 concentrations on both sides of the ether screen compared to using the anesthesia machine O2 blender set at 30%. The differences are substantive because each 1% increase in the ambient O2 concentration increases the combustion rate of cotton by 15%. The use of a Venturi device to regulate O2 concentrations in the presence of an ignition source during head and neck surgery is not recommended. We advocate for anesthesia machine manufacturers to provide an integrated O2 blender for the auxiliary gas outlet of all their products as a fire safety measure.
Horn et al. (Thu,) studied this question.
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