Pulmonary vascular effects of trinitroglycerin and isosorbide dinitrate after cardiopulmonary bypass

We have compared the systemic and right ventricular haemodynamic effects of trinitroglycerin (TNG) and isosorbide dinitrate (ISDN) in patients recovering from coronary artery bypass grafting. Each of the 16 patients was given increasing i.v. doses of the two nitrates in a random order and double blind fashion until the target of a 25% decrease in mean pulmonary artery pressure (MPAP) was achieved. Total doses of TNG 9 (6-12) micrograms kg-1 (mean, 95% confidence interval) and ISDN 148 (76-220) micrograms kg-1 were given during infusions of 22 (18-25) min and 34 (28-41) min duration, respectively. The target decrease in MPAP was produced with infusion rates of TNG 0.5 (0.4-0.7) micrograms kg-1 min-1 and ISDN 5.8 (4.1-7.5) micrograms kg-1 min-1. These doses produced similar acute decreases in MPAP and similar effects on pulmonary and systemic vascular resistances and systemic and right ventricular haemodynamic variables. We conclude that TNG is more than 10 times as potent as ISDN in its acute haemodynamic effects in cardiac surgical patients in the immediate postoperative period. Both nitrates have relatively greater effects on the pulmonary than the systemic vasculature.