Hemodynamic effects of intravenous nitroglycerin: importance of the delivery system

Twenty patients about to undergo elective coronary artery bypass grafting entered a randomized double-blind trial comparing the hemodynamic effects of intravenous nitroglycerin (IV NTG) (0.5 micrograms/kg/min) (n = 9) versus placebo (n = 11). After a 20-min infusion period mean arterial pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure, stroke index, and left ventricular stroke work index were significantly decreased by NTG. Cardiac index was unchanged despite a marked reduction of filling pressures, indicating improved ventricular function. The endocardial viability ratio (DPTI/SPTI) was improved by NTG, suggesting a favorable alteration of myocardial oxygen balance. Three additional patients received a larger dose of NTG, (0.1 micrograms/kg/min). The hemodynamic effects were similar to, but more profound than, those noted at 0.5 micrograms/kg/min. The effects of IV NTG described here are compatible with a predominant venodilator effect of NTG and occurred at a dose previously reported to cause little or no hemodynamic change in a similar group of patients. We attribute the apparent increased potency of IV/NTG observed in our study to the use of an infusion system that does not absorb NTG. Previous investigators have used infusion systems containing polyvinyl chloride (PVC) plastic, a substance that avidly adsorbs NTG. The resultant decrease in the administered dose of NTG renders dose-response data invalid when PVC-containing systems are used to deliver NTG.