Study Objective: A sevoflurane vaporizer dial setting of 1.9% was previously found to maintain the end-expired sevoflurane concentration (Et(sevo)) at 1.3% during maintenance of anesthesia for procedures up to one hour with an O2 FGF of 1 L/min. We examined whether applying these parameters could simplify low-flow sevoflurane anesthesia after overpressure induction using two slightly different techniques. Design: Prospective clinical study. Setting: Large teaching hospital. Patients: Sixteen patients receiving general anesthesia for a variety of peripheral procedures. Interventions: Anesthesia was induced with overpressure with sevoflurane (8%) in an 8 L · min-1 O2/N2O mixture (30%/70%). After a laryngeal mask airway (LMA) was placed, fresh gas flow (FGF) was lowered to 1 L · min-1 using O2 and N2O (FiO2 30%) with patients breathing spontaneously. In group I patients (n = 8), the vaporizer dial was set at 1.9% at the same time the FGF was lowered. In group II patients (n = 8), the vaporizer was turned off until Et(sevo) had decreased to 1.3%, after which the dial was set at 1.9%. The course of Et(sevo) in the two groups was examined. Measurements and Main Results: In group I, Et(sevo) after 3 min was 4.88 ± 1.12%. Et(sevo) decreased slowly after reduction of FGF to 1.83 ± 0.19%, 1.59 ± 0.18%, and 1.52 ± 0.19% at 10, 20, and 30 min, respectively. In group II, Et(sevo) after 3 min was 4.34 ± 0.84%, and decreased more rapidly after reduction of FGF to 1 L · min-1 than in group I. Et(sevo) was 1.40 ± 0.09%, 1.40 ± 0.11%, and 1.38 ± 0.13% at 10, 20, and 30 min, respectively. Conclusions: After high-flow overpressure induction with sevoflurane, a single change in vaporizer setting (to 1.9%) and FGF (to 1 L · min-1) suffices for the Et(sevo) to approach the predicted Et(sevo) (1.3%) within 10-15 min; thereafter the Et(sevo) remains nearly constant. As expected, the predicted Et(sevo) is attained slightly faster when the vaporizer is temporarily turned off. Clinically applying previously derived pharmacokinetic parameters simplifies low-flow sevoflurane anesthesia after overpressure induction. (C) 2000 Elsevier Science Inc.
- Anesthetic techniques
- Anesthetics, volatile
- Low-flow anesthesia
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine