Effects of nifedipine on the hemodynamic response to clamping and declamping of the abdominal aorta in dogs.

Clamping and declamping of the infrarenal abdominal aorta may adversely affect cardiovascular function, particularly in the presence of heart disease. This effect may be further altered by drugs used in the treatment of symptomatic coronary artery disease. The effect of nifedipine on the hemodynamic response to aortic clamping and declamping was determined in 12 dogs anesthetized with 50% nitrous oxide and 0.6% end-tidal isoflurane and monitored with aortic, left ventricular (LV), and thermodilution pulmonary artery catheters. Six dogs received a nifedipine bolus of 100 micrograms/kg followed by an infusion of 4 micrograms/kg/min. Six dogs did not receive any nifedipine and served as controls. Before clamping, nifedipine produced immediate decreases in arterial pressure, systemic vascular resistance (SVR), and LV dP/dt, and a modest increase in cardiac output (CO). During aortic clamping, nifedipine-treated dogs demonstrated marked increases in heart rate (HR), dP/dt, and CO while maintaining a low SVR. There were no significant changes upon declamping. The nifedipine-treated animals maintained a high CO and low SVR. Thus, nifedipine greatly altered the hemodynamic responses to aortic clamping and declamping. Awareness of these alterations is important when caring for patients being treated with nifedipine who are undergoing aortic surgery.