Respiratory patterns in anaesthetised dogs during surgery

The respiratory activity of spontaneously breathing dogs undergoing surgery during halothane/nitrous oxide/oxygen or methoxyflurane/nitrous oxide/oxygen anaesthesia was studied using a spirometer system. Respiratory tidal and minute volumes were directly related to body-weight under methoxyflurane but under halothane anaesthesia only the tidal volumes could be correlated with body-weight. Periodic deep breaths were seen in about one-third of the animals anaesthetised with methoxyflurane but were seldom seen in animals under halothane anaesthesia. Physiological dead-space remained constant for each animal during anaesthesia.