Time to Loss of Preoxygenation in Emergency Department Patients

In patients requiring emergency rapid sequence intubation (RSI), 100% oxygen is often delivered for preoxygenation to replace alveolar nitrogen with oxygen. Sometimes, however, preoxygenation devices are prematurely removed from the patient prior to the onset of apnea, which can lead to rapid loss of preoxygenation. We sought to determine the elapsed time, on average, between removing the oxygen source and the loss of preoxygenation among non–critically ill patients in the emergency department (ED). We conducted a prospective, crossover study of non–critically ill patients in the ED. Each patient received two identical preoxygenation trials for 4 min using a non–rebreather mask with oxygen flow at flush rate and a nasal cannula with oxygen flow at 10 L/min. After each preoxygenation trial, patients underwent two trials in random order while continuing spontaneous breathing: 1) removal of both oxygen sources and 2) removal of non–rebreather mask with nasal cannula left in place. We defined loss of preoxygenation as an end-tidal oxygen (exhaled oxygen percentage; EtO2) value