The effect of isoflurane, halothane, sevoflurane, and thiopental/nitrous oxide on respiratory system resistance after tracheal intubation.

Abstract

After tracheal intubation, lung resistance and therefore respiratory system resistance (R[rs]) routinely increase, sometimes to the point of clinical bronchospasm. Volatile anesthetics generally have been considered to be effective bronchodilators, although there are few human data comparing the efficacy of available agents. This study compared the bronchodilating efficacy of four anesthetic maintenance regimens: 1.1 minimum alveolar concentration (MAC) end-tidal sevoflurane, isoflurane or halothane, and thiopental/nitrous oxide. Sixty-six patients underwent tracheal intubation after administration of 2 microg/kg fentanyl, 5 mg/kg thiopental, and 1 mg/kg succinylcholine. Vecuronium or pancuronium (0.1 mg/kg) was then given to ensure paralysis during the rest of the study. Postintubation R(rs) was measured using the isovolume technique. Maintenance anesthesia was then randomized to thiopental 0.25 mg x kg(-1) x min(-1) plus 50% nitrous oxide, or 1.1 MAC end-tidal isoflurane, halothane, or sevoflurane. The R(rs) was measured after 5 and 10 min of maintenance anesthesia. Data were expressed as means +/- SD. Maintenance with thiopental/nitrous oxide failed to decrease R(rs), whereas all three volatile anesthetics significantly decreased R(rs) at 5 min with little further improvement at 10 min. Sevoflurane decreased R(rs) more than either halothane or isoflurane (P < 0.05; 58 +/- 14% of the postintubation R(rs) vs. 69 +/- 20% and 75 +/- 13%, respectively). After tracheal intubation in persons without asthma, sevoflurane decreased R(rs) as much or more than isoflurane or halothane did during a 10-min exposure at 1.1 MAC.