Recent studies have shown that end tidal oxygen (ETO2) monitoring can be useful to determine the adequacy of preoxygenation. No study has assessed the correlation between ETO2 values obtained during preoxygenation to predict the PaO2 in patients undergoing RSI in the ED. Our objective was to determine whether a novel equation using the ETO2 at the end of preoxygenation could reliably estimate the partial pressure of arterial oxygen (PaO2) in critically-ill ED patients undergoing RSI.

Rapid Sequence Intubation (RSI) is the preferred and most commonly-used method of definitive airway management among critically ill emergency department (ED) patients requiring intubation. Adequate preoxygenation is intended to prolong the safe apnoeic period. Optimal preoxygenation for ED patient undergoing RSI is best described as a two-part process of denitrogenation of the functional residual capacity (FRC) and the formation of an oxygen reservoir within the alveoli. End-tidal O2 (EtO2) has been shown to be a reliable surrogate marker for denitrogenation. Most of the literature supporting EtO2 as an adequate maker of adequate preoxygenation has been conducted in the operating room setting. This population varies significantly from the population requiring endotracheal intubation in the ED. Our study aim was to show that the use of a gas analyzer measuring the fraction of inspired oxygen (FiO2) and EtO2 during the preoxygenation phase of ED RSI can reliably predict the minimal PaO2 at the end of the ED preoxygenation period.

Inclusion Criteria:

• All patients undergoing rapid sequence intubation.

Exclusion Criteria:

• Patients presenting to the emergency department in cardiac or traumatic arrest
• Patients who received bi-level positive airway pressure (BiPAP) as the primary delivery of preoxygenation.

Emergency department patients with a need for endotracheal intubation.