Effects Of Carbon Dioxide And Halothane On Compliance And Pulmonary Resistance During Cardio-Pulmonary Bypass

Lung-mechanics during and at the end of cardio-pulmonary bypass were studied in seventeen patients operated upon for acquired or congenital heart disease. Pulmonary resistance to gasflow, volume-pressure ratios and work of breathing were continuously measured with the aid of a respiratory analogue computer. A special calibrating device was used for frequent calibrations with the patient's respiratory gas. Measurements were made at constant blood gas tensions but with varying fractions of inspired carbon dioxide. The effect of halothane as well as the influence of the patient's circulatory situation were analysed. Hypocapnia of the airways resulted in an increase in pulmonary resistance, while ventilation with a 6.5% carbon dioxide mixture in air-oxygen caused a decrease in resistance with 19 to 71% as compared to hypocapnic conditions. An increase of compliance occurred in the majority of the patients with carbon dioxide. Compliance was generally relatively uninfluenced during the operative and postoperative course. A decrease occurred only in those patients where extra-pulmonary factors were in operation as accumulation of fluid in the chest or left heart failure. The breath to breath analytic technique utilized in the study permitted the demonstration of rapid changes in the volume-pressure relationship occurring simultaneously with increasing left atrial pressure, left heart failure, an acute overload of the lungs with blood or a non-satisfactory general circulation. Halothane added to the airway caused a bronchodilatation which was especially evident during airway hypocapnia. Halothane seemed to reverse the bronchodilatatory effect of hypercapnia. The reason for this is not clear, but it is believed that halothane might block some of the adrenergic receptors through which carbon dioxide exerts its action. Further investigations of this problem are necessary.