Comparison of respiratory characteristics during enflurane and halothane anaesthesia

The effects of enflurane on certain respiratory characteristics were compared with those of halothane in 70 patients during anaesthesia with spontaneous breathing using a specially designed circuit. The rate of respiration with enflurane (mean 22 b.p.m.) was slower than with halothane (mean 31 b.p.m.; P less than 0.001) and the tidal volume greater (enflurane mean 240 ml, halothane 180 ml; P less than 0.05). There was no statistically significant difference in the minute volume of ventilation or end-tidal carbon dioxide concentration between the two agents. The effects of a narcotic premedication were observed in 16 patients in the study. The main effect was to produce slowing of respiratory rate (enflurane mean 16 b.p.m.; halothane 18 b.p.m.). The value of the respiratory pattern compared with the measurement of heart rate and arterial pressure as a clinical guide during anaesthesia is discussed.