[Pre-oxygenation in morbidly obese patients].

Background: Spontaneous respiration with 100% oxygen prior to induction of anaesthesia (preoxygenation) may enable safe management of an apnoeic phase. In the majority of patients, three minutes of inhalation of 100% of oxygen should result in almost complete (>90%) saturation of FRC. However, this may not be true in morbidly obese, because of their limited FRC and oxygen reserve.

Methods: This was a prospective, non-randomised study in morbidly obese patients (BMI >40 kg m2). All patients were positioned in a 25 degrees head-up position, and were asked to breathe 100% O2 (flow rate 8 L min(-1)) via a tight face mask. We measured the time from the beginning of inhalation of 100% O2, to achievement of E(T)O2 >90%.

Results: Forty-three patients with a mean BMI of 47 kg m(-2) were enrolled to the study. The mean time to E(T)O2 >90% was 295 sec, but in only 25% of patients was the time shorter than 3 min. Based on the results obtained, we estimated that the safe time for pre-oxygenation in 95% of morbidly obese patients should be 450 sec.There was no correlation between BMI, weight, age, and the time taken to achieve E(T)O2 > 90%.

Conclusion: We recommend pre-oxygenating morbidly obese patients for longer than those with standard body weight. Eight minutes of 100% oxygen inhalation should be effective in the majority of these patients.