Influence of nitrous oxide on induction of anaesthesia with sevoflurane

Nitrous oxide is often used during inhalation induction of anaesthesiawith sevoflurane. Although the value of using nitrous oxideduring inhalation induction with other volatile anaestheticshas been studied, the popularity of sevoflurane induction andthe different characteristics of this agent make a study ofthe combination of nitrous oxide with this agent of interest.We compared induction times, oxygenation, and excitatory eventsduring inhalation induction of anaesthesia using sevoflurane,with and without nitrous oxide. We studied 64 female patients,randomly allocated to receive inhalation induction of anaesthesiausing sevoflurane with or without 50% nitrous oxide in the freshgas, using a co-axial breathing system (Mapleson D) and a freshgas flow rate of 3–6 litre min^–1. Mean time to inductionof anaesthesia (fall of an outstretched arm) was 102 s in bothgroups, but excitation (limb or head movement) was more frequentin those receiving nitrous oxide (10 patients) than in thosereceiving oxygen only (five patients) (P<0.05). Oxygenationwas similar in both groups. We conclude that nitrous oxide confersno advantage when anaesthesia is induced with sevoflurane inthis way. Br J Anaesth 2001; 87: 286–8