End-Tidal Oxygen as an Effective Noninvasive Measure of Preoxygenation during Rapid Sequence Intubation in the Emergency Department

Abstract

Background: Preoxygenation is intended to extend the duration of apnea until desaturation occurs. End-tidal oxygen (ETO₂) is the standard for measuring preoxygenation, however, peripheral capillary oxygen saturation (SpO₂) is used more commonly within the emergency department.

Objective: The primary aim was to determine whether patients were optimally preoxygenated as measured by ETO₂ vs. SpO₂ during rapid sequence intubation. Secondary aims investigated changes in these measurements before and after intubation and whether patient characteristics influenced the likelihood of preoxygenation success as measured by each of the modalities.

Methods: A multicenter, prospective observational study of a convenience sample of patients undergoing rapid sequence intubation was performed. ETO₂ and SpO₂ were recorded at the cessation of preoxygenation (T₁) and intubation completion (T₂). Optimal preoxygenation was defined by an observed ETO₂ level ≥ 90% and SpO₂ level equal to 100% at T₁.

Results: Thirty patients were intubated and included in the analysis. Median ETO₂ and SpO₂ at T₁ were 90.5% (interquartile range 86-93%) and 100% (interquartile range 97-100%), respectively. Preoxygenation success rates as measured by ETO₂ and SpO₂ were 56.7% and 53.3%, respectively (p = 0.431). The mean (SD) decrease in ETO₂ during the intubation attempt was larger and more variable than that for SpO₂ (25.8% [22.5%] vs. 2.1% [3.3%]; p < 0.001). Patient age, sex, and body mass index were not associated with likelihood of preoxygenation success for either modality.

Conclusions: Preoxygenation success was similar when measured by strict ETO₂ and SpO₂ criteria. ETO₂ is more sensitive to periods of apnea than SpO₂ and may serve as an early indicator of an imminent desaturation event.

Keywords: end-tidal oxygen; peripheral capillary oxygen saturation; preoxygenation; rapid sequence intubation.