Guinea-pig tracheal responsiveness in vitro following general anaesthesia with halothane

Halothane and isoflurane induce potent bronchodilation during general anaesthesia and have been used successfully during status asthmaticus. The aim of this study was to determine whether airway hyporesponsiveness was prolonged after halothane administration. Sixteen guinea-pigs were submitted for 2 h to either 1.5% halothane in oxygen or 100% oxygen, and were killed 24 h later to elicit isometric tracheal contractions in organ baths with various agonists. Cumulative concentration-response curves to histamine or to KCl and contractions evoked with acetylcholine 1 mM (4.7 +/- 0.8 vs 4.6 +/- 0.5 g) or carbachol 10 microM in calcium-free buffer (4.3 +/- 0.6 vs 4.4 +/- 0.6 g) exhibited no difference between groups. Moreover, when 4% halothane or 4.6% isoflurane were directly bubbled through the organ baths, a significant decrease (13 +/- 1% and 37 +/- 2%) of maximal contractions evoked with acetylcholine and KCI, respectively, was obtained but these relaxant effects did not persist 30 min after cessation of anaesthetic. These results indicate that, even though halothane induces transient airway hyporesponsiveness in vitro, previous halothane anaesthesia in guinea-pigs does not alter subsequent tracheal responsiveness assessed in vitro. Our findings may explain the transient renewal of bronchospasm reported during intermittent periods off halothane in status asthmaticus.