Isocapnic hyperpnoea accelerates recovery from isoflurane anaesthesia

Abstract

Background. Hyperventilation should speed up elimination of volatile anaesthetic agents from the body, but hyperventilation usually results in hypocapnia. We compared recovery from isoflurane anaesthesia in patients allowed to recover with assisted spontaneous ventilation (control) and those treated with isocapnic hyperpnoea. Methods. Fourteen patients were studied after approximately 1 h of anaesthesia with isoflurane. Control patients were allowed to recover in the routine way. Isocapnic hyperpnoea patients received 2-3 times their intraoperative ventilation using a system to maintain end tidal PCO2 at 45-50 mm Hg. We measured time to removal of the airway and rate of change of bispectral index (BIS) during recovery. Results. With isocapnic hyperpnoea, the time to removal of the airway was markedly less (median and interquartile range values of 3.6 (2.7-3.7) vs 12.1 (6.8-17.2) min, P<0.001); mean (SD) BIS slopes during recovery were 11.8 (4.4) vs 4.3 (2.7) min-1 (P<0.01) for isocapnic hyperpnoea and control groups, respectively. Isocapnic hyperpnoea was easily applied in the operating room. Conclusions. Isocapnic hyperpnoea at the end of surgery results in shorter and less variable time to removal of the airway after anaesthesia with isoflurane and nitrous oxide.