Cardiovascular alterations in severe pregnancy-induced hypertension: effects of intravenous nitroglycerin coupled with blood volume expansion.

Control of blood pressure in severe pregnancy-induced hypertension has often relied on agents with an unpredictable onset and duration of action. Because intravenous nitroglycerin is a potent, rapidly acting agent with a hemodynamic half-life measured in minutes, we evaluated its cardiovascular effects with and without volume expansion in six patients with severe pregnancy-induced hypertension. Nitroglycerin alone reduced mean arterial pressure by 27.5% without any significant changes in heart rate, central venous pressure, or stroke volume. The pulmonary capillary wedge pressure fell from 9 +/- 3 to 4 +/- 2 mm Hg (p less than 0.05) while the cardiac index decreased from 3.51 +/- 0.67 to 2.87 +/- 0.76 L/min X m2. Oxygen delivery fell significantly (p less than 0.05), from 617 +/- 78 to 491 +/- 106 ml/min X m2. While volume expansion alone had no effect on mean arterial pressure, the combination of blood volume expansion and nitroglycerin resulted in a marked resistance to the hypotensive effect of nitroglycerin. Cardiac index, pulmonary capillary wedge pressure, and oxygen utilization were not significantly different from baseline values when volume expansion preceded nitroglycerin. We conclude that the ease with which nitroglycerin reduces blood pressure is dependent on the individual patient's volume status. Although volume expansion allows one to maintain cardiac index, pulmonary capillary wedge pressure, and oxygen utilization when used in combination with nitroglycerin, this benefit may be offset by a concomitant reduction in hypotensive capability.