Effect of increased body mass index and anaesthetic duration on recovery of protective airway reflexes after sevoflurane vs desflurane†

Increased BMI may increase the body's capacity to store potent inhaled anaesthetics, more so with more soluble agents. Accordingly, we asked whether increased BMI and longer anaesthesia prolonged airway reflex recovery. We measured time from anaesthetic discontinuation until first response to command (T1); from response to command until ability to swallow (T2); and from anaesthetic discontinuation to recovery of ability to swallow (T3) in 120 patients within three BMI ranges (18-24, 25-29, and >= 30 kg m(-2)). All received sevoflurane or desflurane, delivered via an LMA. T1 and T3 after sevoflurane exceeded T1 and T3 after desflurane: 6.6 (sd 4.2) vs 4.0 (1.9) min (P < 0.001), and 14.1 (sd 8.3) vs 6.1 (2.0) min (P < 0.0001). T3 correlated more strongly with BMI after sevoflurane (28 s per kg m(-2), P=0.02) than desflurane (7 s per kg m(-2), P=0.03). Regarding T2, patients receiving sevoflurane with BMI >= 30 kg m(-2) were less often able to swallow 2 min after response to command than were those with BMI 18-24 or 25-29 kg m(-2) (3/20 vs 10/20 or 9/20, P < 0.05). Each sevoflurane MAC-hour delayed T3 by 4.5 min (268 s) (R=0.46, P < 0.001) whereas each desflurane MAC-hour delayed T3 by 0.2 min (16 s) (R=0.10, P=0.44). Prolonged sevoflurane administration and greater BMI delay airway reflex recovery. The contribution of BMI to this delay is more pronounced after sevoflurane than desflurane.