[Co-administration of nitrous oxide reduces the pressor response against oro-tracheal intubation during induction of anesthesia with propofol infusion at a low rate].

This study investigated the effect of co-administration of nitrous oxide on the cardiovascular changes during induction of anesthesia with propofol infusion at a low rate. Sixty patients undergoing general anesthesia were randomly allocated into two groups, and received the inhalation of 100% oxygen (group 1) or 60% nitrous oxide and oxygen (group 2) via face mask for 3 minutes before administration of propofol at 15 mg.kg-1.hr-1. After beginning of propofol infusion, patients inhaled each gas continuously and the loss of response to simple commands by the anesthesiologist was considered as hypnosis. The dose and time for achieving hypnosis were determined, and non-invasive blood pressure, heart rate and arterial oxygen saturation were recorded during induction of anesthesia. Cardiovascular changes during induction were not different between the two groups except mean and diastolic blood pressure immediately after oro-tracheal intubation [126 +/- 21 vs. 113 +/- 21 mmHg and 108 +/- 21 vs. 95 +/- 19 mmHg, respectively (mean +/- SD)]. The dose of propofol and the time for achieving hypnosis showed no significant difference (73 +/- 20 vs. 68 +/- 19 mg and 4.8 +/- 1.0 vs. 4.4 +/- 1.0 min, respectively). Almost all patients were sedated with inhalation of nitrous oxide before infusion of propofol, but no additive effect was observed with nitrous oxide and propofol. Co-administration of nitrous oxide during propofol infusion at a low rate was an effective method to avoid undesirable pressor responses against oro-tracheal intubation without causing adverse cardiovascular depression.