Single vital-capacity and successive tidal-volume breathing of sevoflurane in induction of anesthesia for tracheal intubation in gynecologic patients

Abstract

Background: The optimal end-tidal concentrations of sevoflurane in induction of anesthesia for tracheal intubation have been widely studied and discussed. Single vital-capacity breathing of a high concentration of inspiratory sevoflurane rapidly elevates the end-tidal concentration to cause loss of consciousness, although it does not bear relation to proportional body or brain uptake. This study was designed to investigate the time effect of fast wash-in of alveolar sevoflurane in induction of anesthesia for tracheal intubation with single vital-capacity and ensuing tidal-volume breathing in gynecologic patients.

Methods: Thirty-six ASA I-II patients undergoing gynecologic surgeries under general anesthesia were included in the study. Prior to anesthesia, they were instructed on the vital capacity technique for induction with prior primed 7.2% inspiratory sevoflurane in 6 L/min oxygen in the breathing circuit. Immediately after loss of consciousness, assisted ventilation with fixed 3.5% sevoflurane in oxygen was applied to patients in groups 1 and 2 for 3 minutes, and for 4.5 minutes in group 3. Patients in group 2 received fentanyl 1.5 mug/kg before induction. In all patients, tracheal intubation was performed following succinylcholine 1.5 mg/kg. Inspiratory and end-tidal concentrations of sevoflurane, blood pressure and heart rate were recorded.

Results: All patients achieved vital capacity induction uneventfully, of whom two-thirds needed a second or third breath. The induction time was 60.6 +/- 19.2 seconds and could be reduced to 48.3 +/- 17.9 seconds with fentanyl pretreatment. The end-tidal concentration of sevoflurane was 2.68 +/- 0.20% after 4.5 minutes of ventilation with 3.5% sevoflurane, at which concentration the intubation-induced hemodynamic responses could not be suppressed.

Conclusion: This study demonstrated that vital-capacity induction with a high concentration of sevoflurane is a safe and feasible technique for our female patients. The end-tidal 1.5 minimum alveolar concentration sevoflurane following 4.5 minutes of tidal-volume ventilation did not suppress intubation-induced hemodynamic responses. Pretreatment with fentanyl helped to shorten the induction time and provide better hemodynamic control for tracheal intubation.