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Ann Thorac Surg 1985;39:61-67
© 1985 The Society of Thoracic Surgeons

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Articles

A Comparison of Nitroglycerin and Nitroprusside: II. The Effects of Volume Loading

From the Divisions of Cardiovascular Surgery, Biochemistry, Anesthesia, and Nuclear Cardiology, Toronto General Hospital and University of Toronto, Toronto, Ont, Canada

Accepted for publication July 11, 1984.

^* Address reprint requests to Dr. Weisel, Cardiovascular Surgery, Toronto General Hospital, 200 Elizabeth St, Eaton N 13-224, Toronto, Ont, Canada M5G 1L7

The treatment of postoperative hypertension with nitroglycerin or nitroprusside reduces cardiac filling, and volume loading is required to maintain hemodynamic and metabolic stability. Postoperative hypertension (mean arterial pressure greater than 95 mm Hg) developed in 33 patients who were randomized to an initial infusion of nitroglycerin or nitroprusside in a crossover trial. Volume loading (a rapid infusion of 250 to 500 ml of colloid to raise the left atrial pressure 2 to 4 mm Hg) was instituted prior to hypertension and again following the crossover trial during the infusion of nitroglycerin (11 patients) and nitroprusside (13 patients).

Volume loading increased left ventricular end-diastolic volume index (LVEDVI) as documented by nuclear ventriculography, cardiac index (CI), and left ventricular stroke work index (LVSWI). Although CI was higher (p < 0.01) with nitroprusside at any level of LVEDVI, myocardial performance (the relation between LVSWI and LVEDVI) was not different. Diastolic compliance (the relation between left atrial pressure and LVEDVI) was increased (p < 0.01) with nitroglycerin. Myocardial metabolism was assessed by calculating myocardial lactate flux (MV·L), the product of myocardial lactate extraction and coronary sinus blood flow by the thermodilution technique. Volume loading increased MV·L during nitroglycerin therapy and decreased (p < 0.01) MV·L during nitroprusside therapy.

Volume loading restored preload and increased CI with both nitroglycerin and nitroprusside. Only nitroglycerin improved myocardial lactate utilization. Nitroglycerin is the preferred vasodilator when ischemia is suspected after coronary bypass operations.

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