The Effects of Tolazoline, Nitroprusside, Nitroglycerin, Isoproterenol and Hydralazine on Pulmonary Circulation Early after Heart Valve Replacement

Summary

The choice of an optimal vasodilator therapy in the management of patients with pulmonary hypertension remains controversial, particularly after cardiac surgery. Accordingly, we compared the effects of various drugs on the pulmonary vascular resistance in 12 patients with pulmonary hypertension prior to surgery. The hemodynamic studies were carried out 24 hours after operation in clinically stable patients under respiratory support (paCO2 35-38 mmHg, arterial O2 saturation 92% to 98%). After control measurements, the agents were administered in the following sequence: tolazoline 2.5 μg/kg/min, nitroprusside 2.5 μg/kg/min, nitroglycerin 1 μg/kg/min, isoproterenol 0,015 μg/kg/min and hydralazine 0.1 mg/kg. The arterial blood pressure, heart rate and cardiac index (CI) were allowed to return to control levels between the drugs. The systemic vascular resistance index decreased significantly with all drugs (respectively 34%, 40%, 20%, 34% and 33%) and Cl increased by 30%, 25%, 14%, 34% and 26% respectively. Pulmonary vascular resistance index (PVRI), elevated during control (580 ± 150 dynes × sec × cm^-5 × m², was significantly reduced by tolazoline (-24%), nitroprusside (-46%), nitroglycerin (-26%), isoproterenol (-27%), but not by hydralazine (+5% NS) (all values p < 0.05).

The analysis of these results, after correcting for the decrease in PVRI induced by increasing Cl, allows comparison of the effect of these drugs on the pulmonary vasculature. Nitroprusside and nitroglycerin decrease PVRI much more than expected by the increased Cl; isoproterenol and tolazoline show a direct vasodilator action but less pronounced than with the 2 former drugs and hydralazine increases PVRI despite an increased Cl. In conclusion, in patients with increased pulmonary vascular resistance after valve replacement, nitroprusside and nitroglycerin are the most effective pulmonary vasodilators and should be considered first choice drugs particularly if filling pressures and systemic vascular resistances are high. Tolazoline and isoproterenol should be used in patients with low systemic pressures and Cl. Hydralazine appears contraindicated in both clinical situations.

Key words

Cardiac valve replacement - Pulmonary vascular resistance - Pulmonary hypertension - Postoperative treatment