The Hypotensive Response to Rapid Intravenous Administration of Hypertonic Solutions in Man and in the Rabbit

Abstract

Transient hypotension was observed in patients after rapid i.v. mannitol (25%) administration in clinical doses. These studies were conducted to determine the mechanism for the hypotension, to determine dose and rate of injection response curves in rabbits, and to determine which vascular beds were most reactive. Studies in 6 patients showed mean decreases in blood pressure of 23 .+-. 6.0% (.+-. SE] and in total peripheral resistance of 38 .+-. 7% after infusion of mannitol. Studies in 18 patients during cardiopulmonary bypass with mechanically fixed cardiac output demonstrated decreased in mean blood pressure of 30 .+-. 5 to 40 .+-. 3%, depending on dose and rate of administration of mannitol. Patients not on bypass compensated for large decreases in total peripheral resistance by increases in cardiac output (3.6 .+-. .4 at baseline to 4.4 .+-. .4 l/min) during mannitol-induced hypotension with no change in heart rate. Serum osmolality increased as blood pressure decreased. Significant but clinically unimportant decreases in Na and K ions, hemoglobin, pH, and base excess values were observed. Studies in 18 rabbits showed that the greater the dose or injection rate of mannitol the greater the decrease in blood pressure. Injection of radiolabeled microspheres in rabbits demonstrated a near doubling of blood flow to skeletal muscle tissue during the hypotension. This occurred with both equiosmotic hypertonic glucose (17 .+-. 3 to 32 .+-. 7%) and mannitol (17 .+-. 1 to 31 .+-. 5%), but not after isotonic saline solution. Changes in blood flow to other organ beds were variable and unimportant. The results suggest that hypotension following the i.v. administration of hyperosmotic solutions is due primarily to vasodilation in skeletal muscle.