The Effect of Apnea on Central Airway Oxygen Concentration During Rigid Bronchoscopy: A Prospective Observational Study

Background Airway surgery utilizing a heat source carries a risk of airway fire. Among the airway fire triad of oxidizer, fuel, and ignition source, oxygen concentration is a modifiable risk factor. Rigid bronchoscopy, commonly used during airway surgery, utilizes an open circuit. An open circuit, when combined with jet ventilation, makes measurement of airway oxygen concentration difficult. To decrease airway oxygen concentration, some centers use a pause in jet ventilation to allow airway concentration to decrease; however, the effect of this pause on central airway oxygen levels is not known. Our objective was to better understand changes in central airway oxygen concentration during apnea during rigid bronchoscopy, an important component of fire risk. Methods We designed a prospective observational study of patients requiring rigid bronchoscopy. We utilized jet ventilation with 100% FiO2. To measure central airway oxygen concentration in the distal trachea, we connected a long rigid suction cannula to an oxygen analyzer and passed it through the bronchoscope. When central airway oxygen concentration was >90%, apnea was initiated, and we measured the time required for central airway oxygen concentration to decrease to less than 40%. This was repeated for the right and left main bronchi. Results The average time to reach airway oxygen concentration of less than 40% was 40.9±18.1s (mean±SD), 41.9±19.5s, and 41.6±21.7s for the trachea, right main bronchus, and left main bronchus, respectively. Conclusions We found that after a prolonged period of apnea, many patients had central airway oxygen concentration above levels conventionally considered optimal for airway surgery. This is the first description of this method for monitoring central airway oxygen concentration.