Fifty-nine percent of the VCI group took one breath until loss of consciousness, assessed by loss of response to verbal command. The time for these patients was 39 � 3 seconds. All inhaled induction patients were asleep after <4 breaths. Overall, the average time for loss of consciousness with the inhaled induction was 51 � 4 seconds. The time to loss of consciousness with the IV induction was 81 � 12 seconds (p=0.01). Induction side effects were different with the different techniques. Cough and hiccup were the most common side effects with inhaled induction, whereas movement and blood pressure changes (greater than 20%) were the most common with the IV induction. The overall incidence of side effects for the two methods was similar, 16% inhaled versus 33% IV.

Patients' assessments of the techniques were also obtained. All patients in both groups would have the induction technique again. The induction was rated as pleasant by 97% (31 of 32) of inhaled induction and 100% (24 of 24) of intravenous induction patients. The duration of anesthesia was not different for the two groups (approximately 35 minutes). There were no significant differences in any index of early or intermediate recovery. Digit symbol substitution tests and wakefulness and discomfort visual analog scores during recovery were also not different. The number of patients experiencing any nausea (VAS > 0) was higher in the inhaled induction group, but the incidence of nausea VAS > 10 was not significantly different. There was no delay in discharge readiness or actual discharge times from the postanesthesia care unit phases 1 or 2 for those patients who experienced nausea. Vomiting did not occur and no antiemetics were given.

The authors outlined those factors that produced the rapid inhaled induction. These were a primed circuit filled before the induction began, the initial use of 8% rather than lower concentrations of sevoflurane, and the use of a vital capacity breath rather than a tidal breathing technique. Nitrous oxide was included in the induction mixture to aid the speed of induction via the second gas and concentration effect. The authors addressed a possible concern that priming the circuit with 75% nitrous oxide with the sevoflurane might lead to the delivery of a hypoxic gas mixture. They analyzed the early induction data and found that the inspired oxygen concentration was 28% and the inspired nitrous oxide concentration was 59%. The inspired and expired sevoflurane concentrations at this time were 6.2% and 4.3%, respectively. The cost of priming the circuit for a vital capacity induction was calculated to be $2.79.

The authors concluded that a sevoflurane vital capacity induction is somewhat faster and provides patient satisfaction similar to a propofol intravenous induction in unpremedicated patients. This technique may be offered as an acceptable alternative for induction of general anesthesia for adult ambulatory surgery.

ABSTRACT Comparison of vital capacity induction with sevoflurane to intravenous induction with propofol for adult ambulatory anesthesia. AUTHORS: Philip BK; Lombard LL; Roaf ER; Drager LR; Calalang I; Philip JH. SOURCE: Anesth Analg. 1999 Sep;89(3):623-7 ABSTRACT: We compared vital capacity inhaled induction (VC) with sevoflurane with i.v. induction with propofol for adult ambulatory anesthesia. Patients were randomly assigned to receive either 8% sevoflurane in 75% N2O/O2 from a primed circuit (VC, 32 patients) or propofol 2-mg/kg bolus (i.v., 24 patients). Times to loss of consciousness (response to command) and induction side effects (airway, hemodynamic, motor) were assessed. Anesthesia was maintained with sevoflurane/N2O via a face mask for both groups. At the end of surgery, recovery times were measured and psychomotor function tests were performed. Patients were also asked to assess the quality of their anesthesia. Of the VC patients, 59% lost responsiveness in one breath, taking 39 +/- 3 s. All VC patients completed the induction, and all measures of induction time were significantly shorter for VC than for i.v. Induction side effects were different in the two groups (cough and hiccough for VC versus movement and blood pressure changes for i.v.), but overall incidences were similar. There were no significant differences in any index of early or intermediate recovery. Mild nausea occurred more often with VC, but no antiemetics were needed, and discharge was not delayed. Patients' assessments of the quality of induction or wake up were not significantly different between VC and i.v. Thus, VC induction with sevoflurane is an acceptable alternative to propofol i.v. induction of general anesthesia for adult ambulatory surgical patients. IMPLICATIONS: A vital capacity induction with sevoflurane produced a faster loss of consciousness and had side effects, recovery times, and patient satisfaction similar to that of a propofol induction in adults undergoing ambulatory surgery.