Combined NRB and Nasal Cannula Oxygen Delivery Is Inferior to Flush Rate NRB for Emergency Preoxygenation

OBJECTIVES: Although preoxygenation with a non-rebreather (NRB) mask at flush rate (≥ 50 L/min) is an effective and straightforward technique, it is not always feasible in situations where airway management must be performed away from the ambulance, when only portable oxygen tanks are available. To achieve a combined total flow of ≥50 L/min, some experts have advocated the use of a NRB mask in combination with a nasal cannula, both at 25 L/min. This technique has not been compared to preoxygenation using flush rate oxygen. This study sought to determine whether preoxygenation using both a NRB mask and nasal cannula at total flow rates of up to 50 L/min is non-inferior to preoxygenation using a NRB mask alone at flush rate.METHODS: We performed an experimental crossover study using healthy volunteers. Participants underwent the following 3-minute preoxygenation trials: NRB at flush rate oxygen; NRB and nasal cannula each at 15 L/min; NRB and nasal cannula each at 25 L/min. Oxygen was delivered via a standard ambulance oxygen system and a wall-mounted flowmeter. The primary outcome was the fraction of expired oxygen (FeO₂), measured at the end of each trial. We compared the FeO₂ obtained using a NRB at flush rate to the other methods using a pre-specified non-inferiority margin of 10%.RESULTS: We enrolled 30 participants. Mean FeO₂ values for NRB at flush rate, NRB + nasal cannula at 15 L/min, and NRB + nasal cannula at 25 L/min were 85% (95% confidence interval [CI] 83-87%), 68% (95% CI 66-71%), and 75% (95% CI 71-78%), respectively. The FeO₂ values achieved using the NRB + nasal cannula at 15 and 25 L/min were inferior to NRB at flush rate (FeO₂ differences of 16%, 95% CI 13% to 20%; and 10%, 95% CI 6% to 14%, respectively).CONCLUSIONS: In healthy volunteers, combining a NRB mask with nasal cannula with each at either 15 L/min or 25 L/min provides inferior preoxygenation compared with an NRB mask alone at flush rate oxygen. When available, flush rate NRB should remain the preferred preoxygenation strategy for spontaneously breathing patients in the prehospital setting.