Vasodilator therapy during coronary artery surgery. Comparison of nitroglycerin and nitroprusside

Intraoperative hypertension is a common problem in patients undergoing myocardial revascularization. Twenty patients who developed acute hypertension after sternotomy were studied. Ten patients received three doses of intravenous nitroglycerin (32, 64, and 96 mcg. per minute), and 10 patients received nitroprusside (20, 40, and 60 mcg. per minute). All patients were anesthetized with morphine, diazepam, nitrous oxide, oxygen, and pancuronium bromide. Five patients in each group also received enflurane. The study compared the effects of nitroglycerin and nitroprusside on systemic hemodynamics, myocardial oxygen supply/demand relationships, and ischemic changes on the electrocardiogram. Both drugs decreased preload and afterload in a dose-related manner. Heart rate increased significantly only with the largest dose of each drug. Myocardial oxygen demand was decreased significantly by both drugs, while the coronary perfusion pressure was decreased more by nitroprusside. Both nitroglycerin and nitroprusside improved left ventricular performance. Nitroglycerin improved ST-segment depression in eight of 10 patients; while nitroprusside improved the ST segments in six patients, and worsened the ST segments in three patients. None of the nitroglycerin group had worsening of the electrocardiographic ST segments. These findings demonstrate that both drugs can control intraoperative hypertensions and can decrease myocardial oxygen demand. Nitroglycerin was shown to improve ischemic changes on the electrocardiogram more often than nitroprusside.