Effect of halothane on bronchial calibre of anaesthetised cattle

A computer-aided forced oscillation technique was used to examine the effects of halothane on bronchial calibre in three adult cows after anaesthesia had been induced with xylazine and thiopentone. The administration of halothane failed to produce bronchodilatation, possibly owing to low resting bronchomotor tone in the animals. However, an increase in expiratory reserve volume, associated with a small fall in airway resistance, was observed, suggesting that changes in elastic recoil may make a significant contribution to changes in airway resistance during anaesthesia. The results also emphasise the importance of relating airway resistance to lung volume.