Effect of halothane and diethyl ether on the circulatory response to carbon dioxide in the isolated perfused cat lung

Constant flow perfusion of the pulmonary circulation was established in isolated cat lungs. These were ventilated with 5% carbon dioxide in oxygen in order to maintain a near-normal carbon dioxide tension and acid-base status in the perfusing blood. The alteration of pulmonary vascular resistance in response to a change in inspired carbon dioxide concentration from 5% to 10% was investigated before, during and after the administration of 1% halothane (in 16 perfusions) or 5% diethyl ether (in 8 perfusions). An increase of inspired carbon dioxide concentration caused a significant increase in pulmonary vascular resistance, but the magnitude of the increase was diminished during the administration of both anaesthetic agents. The response increased again after the anaesthetics were withdrawn. The administration of halothane during ventilation with 5% carbon dioxide caused a significant reduction of pulmonary vascular resistance whilst diethyl ether resulted in a significant increase in this measurement. It is suggested that inhalation anaesthetic agents may increase ventilation/perfusion mismatching by altering the normal vasoconstrictor response to increased alveolar PCO2;