The Annals of Thoracic Surgery, Vol 39, 61-67, Copyright © 1985 by The Society of Thoracic Surgeons
A comparison of nitroglycerin and nitroprusside: II. The effects of volume loading
SE Fremes, RD Weisel, DA Mickle, SJ Teasdale, AP Aylmer, GT Christakis, MM Madonik, J Ivanov, S Houle and PR McLaughlin
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 less
than 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 less than 0.01) with nitroglycerin. Myocardial metabolism
was assessed by calculating myocardial lactate flux (MVL), the product of
myocardial lactate extraction and coronary sinus blood flow by the
thermodilution technique. Volume loading increased MVL during nitroglycerin
therapy and decreased (p less than 0.01) MVL 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.
