In this study, the authors find that a custom-designed oxygen scavenger mask reduces local oxygen concentrations at 18 distinct landmarks across the facial surgical field including the non-perinasal lower face to below the fire threshold on a simulated manikin model. These oxygen concentration reductions were statistically significant at all measured facial landmarks in the masked condition compared a standard unmasked condition. The oxygen concentration measurements were below fire threshold in the masked condition at all three tested flow rates. Oxygen concentration directly correlated with oxygen flow rate in the unmasked condition but not with the mask device, suggesting that an oxygen scavenger mask system may be a useful adjunct for reducing intraoperative fire risk. These findings build on a previous report describing the efficacy of a midfacial seal drape at diverting oxygen from the oculofacial surgical field [8]. An oxygen scavenger mask device may also obviate the limitations of a seal drape for lower facial surgery in reducing intraoperative fire risk.
Previous reports have noted that surgical oxygen levels create a fire hazard when concentration is at or above 23% [9]. In this study, landmarks near the nares and mouth displayed local oxygen concentrations above the fire threshold even at the lowest oxygen flow rate (2 L/min). Landmarks near the eye and neck regions displayed suprathreshold oxygen concentrations at a moderate flow rate (4 L/min), while the forehead and neck only displayed suprathreshold oxygen concentrations at a high flow rate (6 L/min). This pattern of oxygen distribution is likely secondary to the dependent pooling of oxygen. Oxygen is denser than air and, in our experiment, the most dependent parts of the face (i.e. nose and mouth) exhibited the highest local oxygen concentrations at the lowest flow rates [10].
A fire triangle during oculofacial surgery is unavoidable if a patient requires oxygen supplementation and cautery. The prototypes tested this study were constructed from inert silicone that may further add fire-retardant benefit. Currently available drape materials and masks are often constructed from organic materials and therefore can fuel a surgical fire. The chief feature of the prototypes, however, may be their ability to divert pooled oxygen from the operative field. Such a scavenger mask may minimize, but not eliminate, the risk of surgical fire. Further experiments with scavenger devices constructed from other materials are warranted.
Other approaches to surgical fire reduction, such as the use of nonflammable linens or drapes and minimizing or turning off supplemental oxygen prior to cautery, remain valuable. Awareness and understanding of how operating room fires occur are critical. Of note, smoke scavenger devices connected to electrosurgical cautery pens currently exist, but may exacerbate fire risk by drawing oxygen toward the ignition source. That hundreds of operating room fires continue to occur each year in the U.S. corroborates an ongoing need for further thoughtfulness, innovation, and education of fire hazards in the operating room.
One limitation of this study is that it was performed on an anesthesia training manikin that does not recapitulate all aspects of live human surgery. First, the seal of our scavenger mask may be more robust on the synthetic rubber surface of the manikin compared to surgically-prepared human skin, which is usually layered with antiseptic preparation solutions, natural oils and secretions, and condensed breath that may impair the formation of an adequate seal. Additionally, our mask designs are imperfect. They feed and scavenge oxygen in the same space, which may impair oxygenation in a live patient. Their bulkiness may also limit functionality in live human surgery by distorting facial anatomy and possibly interfere with facial surgery. Second, the manikin is immobile and lacks the head movements or breathing patterns of live patients under monitored anesthesia care. Inspiration and exhalation could affect local oxygen concentrations by either drawing oxygen into the airway or blowing oxygen away from the face. Third, facial anatomy varies on a patient-to-patient basis and may deviate from that of the manikin used in this study. We note a paradoxical reduction in oxygen concentration at the 6 L/min flow rate at landmarks 17 and 18, which would not be expected in a live patient. This may be secondary to the fluid dynamic system established by the facial structure of the manikin used in this study. As such, the oxygen distribution patterns observed in this study may differ from those seen in live patients. Formal experiments in human subjects may address many of these limitations and warrant further consideration.
In summary, an oxygen scavenger mask may offer additional protection against intraoperative fire during ambulatory facial surgery. This innovation, along with other pre-existing fire-retardant protocols, may enhance patient fire safety. Further studies that validate these theoretical safety improvements in clinical practice may be useful. Also, ergonomic design modifications that minimize bulk and area of facial coverage that offer optimal comfort and patient fit may be warranted.
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