Ambient Oxygen Concentration Enrichment When Using a Face Mask Connected to the Breathing Circuit Versus a Venturi...

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.