Clinical comparison of sevoflurane and isoflurane when administered with nitrous oxide for surgical procedures of intermediate duration.

The purpose of this study was to compare the haemodynamic effects and emergence times of anaesthesia with sevoflurane with those of isoflurane when the agents were administered with nitrous oxide to adult patients (ASA I and II) undergoing surgery of at least an hour in duration. Fifty patients were randomly assigned to receive either 0.65 minimum alveolar concentration (MAC) (1.3%) sevoflurane or 0.65 MAC (0.8%) isoflurane together with 60% nitrous oxide following induction with thiopentone, fentanyl, and succinylcholine. Systemic blood pressure and heart rate trends were similar for both groups for the duration of anaesthesia. However, differences in systolic blood pressure measurements were noted at one minute after incision (99 +/- 3 mmHg, mean +/- SE, in the sevoflurane group compared with 109 +/- 4 mmHg for isoflurane), and at emergence (125 +/- 3 mmHg for sevoflurane, 134 +/- 3 mmHg for isoflurane), and in diastolic blood pressure measurements at five minutes after intubation (64 +/- 2 mmHg for sevoflurane, 73 +/- 3 mmHg for isoflurane). Recovery of response to command was more rapid after discontinuation of sevoflurane-nitrous oxide (9.9 +/- 1.1 min) than after isoflurane-nitrous oxide (13.9 +/- 1.3 min). Despite earlier emergence, patients who had received sevoflurane did not request postoperative analgesia sooner. We conclude that the purported advantages of sevoflurane, namely haemodynamic stability and rapid emergence, can be expected even when the agent is administered at 0.65 MAC (1.3%) in nitrous oxide to a typical adult surgical population undergoing procedures of intermediate duration (2.3 +/- 0.2 hr).