Anesthetic Uptake of Sevoflurane and Nitrous Oxide During an Inhaled Induction in Children

Abstract

The uptake of sevoflurane and nitrous oxide (N2O) was characterized during the mask induction of anesthesia in healthy children. We assessed concentration and second gas effects by determining the influence of two different inspiratory N2O concentrations on the rate at which the estimated alveolar concentration (FA) increased to the inspired gas concentration (FI). Eighteen children aged 4–12 yr old were randomly assigned to receive a 6% sevoflurane mixture with either a large or a small N2O concentration with balance O2. End-tidal and inspiratory concentrations of respiratory and anesthetic gases were continuously assessed during the induction. The FA/FI for the small N2O was 0.87 ± 0.09 (mean ± sd) and increased to 0.92 ± 0.08 for the large N2O (P < 0.01). Both groups differed significantly at 3, 4, and 5 min. The FA/FI for sevoflurane increased but more slowly than for N2O. The mean only differed significantly at 3 min. Equilibration between FA and FI for N2O and sevoflurane was attained rapidly. Consistent with their respective blood/gas partition coefficients, the FA/FI for N2O increased more rapidly than that for sevoflurane. Increasing FI-N2O produced a leftward shift in gas equilibration curves. A concentration effect was confirmed with N2O and a brief second gas effect, probably explained by the higher solubility of sevoflurane.