Comparison of the Effects of Enoximone and Isoproterenol on Protamine Cardiotoxicity in Anesthetized Dogs

In this study we investigated the effects of isoproterenol and enoximone on protamine cardiotoxicity because administration of protamine for heparin reversal during open heart surgery depresses left ventricular function. Eighteen mongrel dogs were entered into this study. After induction of general anesthesia and a stabilization period, a thermodilution catheter was inserted via the jugular vein. Another 2 catheters were inserted into the left ventricle and femoral artery. Heparin and protamine were used in all animals. Heparin dosage was 300 U/kg, and protamine dosage was 4.5 mg/kg. The animals were divided into 3 groups. Six animals received enoximone (5 μg/kg per min), 6 animals received isoproterenol (0.05 μg/kg per min), and 6 animals received no inotropic agent. Measurements were performed before treatment, 5 min after protamine administration, and at 15-min intervals for 1 h. Cardiac output (CO), mean arterial pressure, pulmonary capillary wedge pressure, first derivative of left ventricular pressure (1±) left ventricular systolic pressure, and heart rate were measured. CO was 1582±34 ml/min in the isoproterenol group (I+P), 1684±61 ml/min in the enoximone group (E+P), and 1471±37 ml/min in the protamine group (P) (p