Incidence and prediction of inadequate preoxygenation before induction of anaesthesia

Preoxygenation aims to obtain an expired oxygen fraction (FEO2)≥90%. Little is known about the incidence and predictors of inadequate preoxygenation in the clinical setting.

Over a 12-month period, 1050 consecutive preoperative patients were prospectively included. Preoxygenation was performed for 3minutes with a facial mask using a machine circuit and 12-L/min oxygen flow. Inadequate preoxygenation was defined as an FEO2<90%. A logistic regression was performed to identify incidence and independent predictors.

The patient characteristics were: age 51±20years, 47% male, BMI of 26±5kg/m(2), and ASA score (median [extremes]) of 2 [1-4]. Inadequate preoxygenation was observed in 589 patients (56%). The effective FiO2 delivered was lower in the patients with inadequate preoxygenation than in those with adequate preoxygenation, 95±3% vs. 98±2%, P<0.001. The difference between the FiO2 and the FEO2 was higher (12±6% vs. 6±3%, P<0.0001) in patients with inadequate preoxygenation compared with those with adequate preoxygenation. The independent risk factors for inadequate preoxygenation were: firstly, bearded male (odds ratio [OR] of 9.1 [2.7-31.4] P<0.001); secondly, beardless male (OR 2.4 [1.6-3.4] P<0.001), thirdly, ASA score of 4 (OR 9.1 [2.6-31.2] P<0.015); fourthly, ASA score of 2-3 (OR 2.4 [1.6-3.4] P<0.015); fifthly, lack of teeth (OR 2.4 [1.2-4.5] P<0.006), and lastly age>55 years (OR 1.8 [1.2-2.7] P<0.005).

Inadequate preoxygenation, defined as an FEO2 <90% despite 3-min tidal volume breathing, was a common occurrence. The predictive factors share an overlap with those previously identified for difficult mask ventilation.