The effects of sodium nitroprusside on the hemodynamics of burn shock: results of an experimental sheep model.

A low cardiac output state is observed following major thermal injury in both experimental and clinical settings. The major determinants of cardiac output are preload, afterload, and the contractile state of the myocardium. The effects of afterload reduction in acute thermal injury are the focus of this experiment. Pure-bred young nonpregnant ewes of the Suffolk strain were utilized to determine the effect of afterload reduction on the cardiac index in experimental burn shock. Four groups of animals were studied; Group 1: unburned control (n = 5); Group 2: unburned-treated with sodium nitroprusside (n = 5); Group 3: 40% burned (n = 9); and Group 4: 40% burned-treated with sodium nitroprusside (n = 9). Pulmonary arterial, intravenous, and bladder catheters were placed in all animals. Following anesthesia with or without a burn, the animals were monitored for 24 hours. Measured and calculated parameters included cardiac index, pulmonary arterial and arterial pressures, pulmonary and systemic vascular resistance indices, shunt, arterial and mixed venous blood gases and pH, and hematocrit. When burned animals with and without nitroprusside were compared, significantly higher cardiac indices, expressed as per cent of baseline, were noted for the sodium nitroprusside-treated group at 8 and 12 hours postburn. The burned-treated animals' cardiac index was not significantly different from control animals' at 8 hours postburn. However, the burned-untreated animals had significantly depressed cardiac indices until 18 hours postburn.(ABSTRACT TRUNCATED AT 250 WORDS)