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

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Abstract
The uptake of sevoflurane and nitrous oxide (N(2)O) 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 N(2)O 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 N(2)O concentration with balance O(2). End-tidal and inspiratory concentrations of respiratory and anesthetic gases were continuously assessed during the induction. The FA/FI for the small N(2)O was 0.87 +/- 0.09 (mean +/- SD) and increased to 0.92 +/- 0.08 for the large N(2)O (P < 0.01). Both groups differed significantly at 3, 4, and 5 min. The FA/FI for sevoflurane increased but more slowly than for N(2)O. The mean only differed significantly at 3 min. Equilibration between FA and FI for N(2)O and sevoflurane was attained rapidly. Consistent with their respective blood/gas partition coefficients, the FA/FI for N(2)O increased more rapidly than that for sevoflurane. Increasing FI-N(2)O produced a leftward shift in gas equilibration curves. A concentration effect was confirmed with N(2)O and a brief second gas effect, probably explained by the higher solubility of sevoflurane.