Nitroglycerin is absorbed in vitro into polyvinyl chloride tubing, and it has been recommended that nitroglycerin be administered intravenously through specialized polyethylene infusion sets. To determine if tubing type is essential to achieve physiologic effectiveness, we studied dose responses to intravenous nitroglycerin in 15 patients with heart failure using standard polyvinyl chloride tubing in seven (group 2) and special polyethylene infusion sets in seven (group 1) (one patient was excluded from analysis because of technical difficulties). We monitored heart rate, blood pressure, right atrial pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output. Cardiac index, systemic and pulmonary vascular resistance, triple index, rate pressure product, stroke volume, stroke volume index, and stroke work index were calculated. Baseline and treatment measurements were obtained from five to 15 minutes after the infusion of 10, 20, 40, and 80 μg of nitroglycerin per minute. Over-all, systolic blood pressure decreased (p < 0.05) about 8 percent and mean blood pressure approximately 12 percent, mean pulmonary artery pressure and mean pulmonary capillary wedge pressure decreased 30 to 40 percent, and the decline in mean right atrial pressure was 35 percent of baseline (all p < 0.05). Heart rate and cardiac index did not change (p > 0.05). Pulmonary vascular resistance decreased slightly (p = 0.07) and systemic vascular resistance significantly (p < 0.05). When the two groups were compared physiologic changes were virtually identical (p < 0.05). Two-way analysis of variance for baseline corrected data proved no differences between tubing sets (p < 0.05), but the infusion concentration rate was highly related to response (p = 0.0001). A significant (p < 0.05) decrease in mean blood pressure and mean right atrial pressure was noted at lower dose rates (20 μg per minute and 40 μg per minute, respectively) in group 1. Beneficial hemodynamic effects in heart failure patients can, then, be predicted to occur at 80 μg per minute infusion rates; these responses seem independent of the type of infusion tubing system employed. Additionally, when patients given intravenous nitroglycerin for various reasons were followed for 48 hours, the majority receiving infusions via polyvinyl chloride tubing (group 2) did not require dosage adjustments. Also, at lower flow rates, more solution than calculated may be delivered when polyethylene tubing infusion sets are employed with volumetric infusion pumps.
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