Effects of halothane and morphine sulfate on myocardial compliance following total cardiopulmonary bypass.

We evaluated the effect on diastolic myocardial compliance of halothane and morphine sulfate using 15 swine placed on total cardiopulmonary and right heart bypass with controlled aortic pressure, heart rate, and left ventricular preload. The animals were divided into three equal groups: (I) regional block anesthesia, (II) morphine sulfate (10 mg/kg), and (III) halothane anesthesia at 0.5%. Myocardial performance was evaluated on right heart bypass following a 30 minute period of total cardiopulmonary bypass before and after administration of the anesthetic agent by measuring stroke volume, left ventricular end-diastolic pressure, and left ventricular end-diastolic volume. All perfusions were at normothermia, at a hematocrit level of 30%, and at a normal arterial Po2. PCO2, and pH. Neither regional block nor morphine sulfate anesthesia significantly depressed the myocardium or changed diastolic compliance. Halothane, however, significantly decreased diastolic compliance so that stroke volume was less at a given left ventricular end-diastolic pressure, but not at a given left ventricular end-diastolic volume. The depression of stroke volume with halothane following cardiopulmonary bypass at equal filling pressures appears to be due primarily to a change in compliance rather than to a change in contractility.