Identification of the Optimal Position of a Nasal Oxygen Cannula for Apneic Oxygenation - A Technical Simulation

Background. In a cannot ventilate cannot intubate situation, careful preoxygenation with high FiO2 allowing subsequent apneic oxygenation can be life-saving. The best position for an oxygen supply line within the human airway at which oxygen insufflation is more effective than standard preoxygenation with a face mask, or comparably effective as intratracheal insufflation, is unknown. Methods. In this experimental study, we compared effectiveness of preoxygenation by placing an oxygen cannula at the nose entrance, through the nose at the soft palatine, or at the base of tongue; as control we used ambient air. We connected a fully preoxygenated test lung on one side to an oximeter with a flow rate of 200ml/min simulating oxygen consumption of a normal adult, and on the other side to the trachea of an anatomically correctly shaped airway manikin over a 20 min observation period five times for each cannula placement in random order. Results. Oxygen percentage in the test lung dropped from 100% in all groups to 53±1% in the ambient air control group, to 87±2% in the nasal cannula group, to 96±2% in the soft palatine group, while it remained at 99±1% in the base of tongue group (p=0.003 for soft palatine vs base of tongue; and p<0.001 between all other groups). Conclusions. When simulating apneic oxygenation in a preoxygenated manikin, oxygen insufflation at the base of tongue kept oxygen percentage at baseline values of 99% demonstrating a complete block for ambient air flowing into the manikin’s airway. Oxygen insufflation at the soft palatine or insufflation via nasal cannula were less effective in regard of this effect.