Effect of Obesity on the Time Required Achieving a FEO2 of 90% during Preoxygenation

Abstract

An end-expiratory oxygen (FEO 2) concentration > 90% is desirable prior to tracheal intubation. We hypothesized that the time required for pre oxygenation to achieve an FEO 2 of 90% was related to patient Body Mass Index (BMI). Seventy-seven consenting patients undergoing a rapid sequence induction were enrolled. After the anesthesia rebreathing circuit was filled with 100% oxygen for 4 min, these unpremedicated patients were instructed to breathe normally following application of a tight-fitting face mask with oxygen flowing at 10 L min-1. End-tidal oxygen and carbon dioxide values were recorded during the pre oxygenation period. Induction of anesthesia was performed when the FEO 2 reached 90% or after 5 min of pre oxygenation in a standardized fashion. The times to achieve an FEO 2 of 90% were 152 ± 57, 136 ± 62 and 136 ± 70 sec in the normal, overweight and obese subgroups, respectively. A total of 7 patients failed to achieve an FEO 2 90% after 5 min of preoxygenation. Four patients also experienced a decrease in SpO 2 < 95% during the apneic period prior to tracheal intubation (3 in the obese group and 1 in the overweight group). The mean BMI (± SD) of the patients who failed to achieve a FEO 2 of 90% was 40 ± 9 kg/ m 2. The time required to achieve an FEO 2 of 90% during preoxygenation period was unrelated to the patient's BMI. However, morbidly obese patients were more likely to experience a fall in their SpO 2 to < 95% during the induction period.