Time to Loss of Preoxygenation in Emergency Department Patients

J Emerg Med. 2020 Nov;59(5):637-642. doi: 10.1016/j.jemermed.2020.06.064. Epub 2020 Aug 5.


Background: 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.

Objective: 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).

Methods: 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 < 70%. We measured EtO2 breath by breath until loss of preoxygenation occurred.

Results: We enrolled 42 patients, median age was 43 years (interquartile range [IQR] 30 to 54 years) and 72% were male. Median time to loss of preoxygenation was 20 s (IQR 17-25 s, 4.5 breaths) when all oxygen devices were removed, and 39 s (IQR 21-56 s, 8 breaths) when the nasal cannula was left in place.

Conclusions: In this population of non-critically ill ED patients, most had loss of preoxygenation after 5 breaths if all oxygen devices were removed, and after 8 breaths if a nasal cannula was left in place. These data suggest that during ED RSI, preoxygenation devices should be left in place until the patient is completely apneic.

Keywords: airway management; denitrogenation; emergency department; intubation; oxygen; preoxygenation.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Cannula*
  • Cross-Over Studies
  • Emergency Service, Hospital
  • Female
  • Humans
  • Intubation, Intratracheal
  • Male
  • Middle Aged
  • Oxygen
  • Oxygen Inhalation Therapy
  • Prospective Studies
  • Respiration, Artificial*


  • Oxygen