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PEDIATRIC ANESTHESIA

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

Department of Pediatric Anesthesiology, La Paz Children’s University Hospital, Madrid, Spain

Address correspondence and reprint requests to Department of Pediatric Anesthesiology, La Paz Children’s University Hospital, Paseo de la Castellana 261, 28046 Madrid, Spain. Address e-mail to luisgoldman{at}terra.es

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.

IMPLICATIONS:The wash-in of sevoflurane and nitrous oxide in healthy children during the mask induction of anesthesia showed a more rapid equilibrium between alveolar and inspired gas concentrations than in adults. Consistent with their respective blood/gas partition coefficients, the alveolar concentration for nitrous oxide increased more rapidly to its inspired concentration than that for sevoflurane. A concentration effect was confirmed with nitrous oxide and a brief, second gas effect, probably explained by the higher solubility of sevoflurane.