Increased lung clearance of isoflurane shortens emergence in obesity: a prospective randomized-controlled trial

There is a concern that obesity may play a role in prolonging emergence from fat-soluble inhalational anaesthetics. We hypothesized that increased pulmonary clearance of isoflurane will shorten immediate recovery from anaesthesia and post-anaesthesia care unit (PACU) stay in obese patients.

After Ethics Review Board approval, 44 ASA I-III patients with BMI>30 kg/m(2) undergoing elective gynaecological or urological surgery were randomized after completion of surgery to either an isocapnic hyperpnoea (IH) or a conventional recovery (C) group. The anaesthesia protocol included propofol, fentanyl, morphine, rocuronium and isoflurane in air/O(2) . Groups were compared using unpaired t-test and ANOVA.

Minute ventilation in the IH group before extubation was 22.6 ± 2.7 vs. 6.3 ± 1.8 l/min in the C group. Compared with C, the IH group had a shorter time to extubation (5.4 ± 2.7 vs. 15.8 ± 2.7 min, P<0.01), initiation of spontaneous ventilation (2.7 ± 2.3 vs. 6.5 ± 4.5 min, P<0.01), BIS recovery >75 (3.2 ± 2.3 vs. 8.9 ± 5.8 min, P<0.01), eye opening (4.6 ± 2.9 vs. 13.6 ± 7.1 min, P<0.01) and eligibility for leaving the operating room (7.1 ± 2.9 vs. 19.9 ± 11.9 min, P<0.01). There was no difference in time for eligibility for PACU discharge.

Increasing alveolar ventilation enhances anaesthetic elimination and accelerates short-term recovery in obese patients.