Continuous Hydralazine Infusion for Afterload Reduction

Impedance reduction with a continuous infusion of hydralazine was evaluated in 20 patients following cardiopulmonary bypass. Patients were selected for therapy when the cardiac index (CI) was less than 2.2 L/m2/min, when the systemic vascular resistance index (SVRI) was greater than 2,500 dyne sec cm-5, or when both conditions were present. No other vasoactive or cardiotonic drugs were used intraoperatively or postoperatively. Responses were measured at 15, 30, 60, 120, 180, and 240 minutes and compared with control measurements. Significant responses appeared by 15 minutes in the mean arterial pressure, CI, and SVRI, which were maximal by 2 hours. At 4 hours, the SVRI was 1,520 +/- 276 dyne sec cm-5 (control, 3,235 +/- 222) and pulmonary vascular resistance index, 365 +/- 102 dyne sec cm-5 (control, 592 +/- 71). The CI was 3.20 +/- 0.29 L/m2/min (control, 1.96 +/- 0.16) and mean arterial pressure, 75 +/- 2.3 mm Hg (control, 92 +/- 2.4). Left atrial, pulmonary artery diastolic, and right atrial pressures increased from control but not significantly: 11.4 +/- 0.8 to 13.3 +/- 1.2 mm Hg, 13.6 +/- 1.6 to 17.2 +/- 1.5 mm Hg, and 6 +/- 1.6 to 9.4 +/- 1.7 mm Hg, respectively. In 16 patients, hydralazine was continued for 24 hours and in 11, the transition to oral therapy was made. Hydralazine by infusion effectively reduces after load, avoids the fluctuations of bolus therapy, and allows the transition to oral therapy if needed.