Background
Obesity is a risk factor for airway-related incidents during anaesthesia. High flow nasal oxygen has been advocated to improve safety in high-risk groups but its effectiveness in the obese population is uncertain. This study compared the effect of high flow nasal oxygen and low flow facemask oxygen delivery on duration of apnoea in morbidly-obese patients.

Methods
Patients undergoing bariatric surgery were randomly allocated to receive either high flow nasal (70 L min-1) or facemask (15 L min-1) oxygen. Following induction of anaesthesia, morbidly-obese patients were apnoeic for 18 minutes or until oxygen saturation dropped to 92%.

Results
Eighty patients were studied (41 high flow nasal oxygen, 39 facemask). Median apnoea duration was 18 minutes in both the high flow nasal oxygen (IQR 18-18 minutes) and the facemask (IQR 4.1-18 minutes) groups. Five patients in the high flow nasal oxygen group and 14 patients in the facemask group desaturated to 92% within 18 minutes. The risk of desaturation was lower in the high flow nasal oxygen group (Hazard Ratio 0.27, 95% CI 0.11-0.65, p=0.007).

Conclusions
In experienced hands, apnoeic oxygenation is possible in the morbidly-obese and was tolerated for 18 minutes by the majority of patients, whether oxygen delivery was high flow nasal or low flow facemask. High flow nasal oxygen reduced desaturation risk compared to facemask oxygen. Desaturation risk is a more clinically relevant outcome than duration of apnoea. Individual physiological factors are likely to be the primary determinant of risk rather than method of oxygen delivery.