Peripheral Vascular Response to Simulated Hemorrhagic Shock during Cardiopulmonary Bypass in Dogs

¹ Department of Physiology and Anesthesiology and the Heart Research Center, Indiana University School of Medicine Indianapolis, Indiana 46202
² Department of Physiology and Anesthesiology and the Heart Research Center, Indiana University School of MedicineIndianapolis, Indiana 46202

The peripheral vascular response to hemorrhagic hypotension was examined in thirteen anesthetized dogs on cardiopulmonary bypass. Nine animals were subjected to 2 or 4 hours of hypotension by decreasing pump output (30ml/kg/min), thereby controlling mean arterial blood pressure at 40 mm Hg. Systemic flow was then returned to prehypotensive levels (100 ml/kg/min), and the animals were observed for 6 more hours. Dynamic venous compliance was determined by occluding the venous outflow catheters and recording the venous pressure rise at a known rate of inflow. Venous compliance, changes in reservoir fluid volume, total peripheral resistance, and mean arterial blood pressure were measured at 30-minute intervals. During the first hour of hypotension there was a marked increase in venous compliance, a decrease in reservoir fluid volume, and an increase in total peripheral resistance. Fluid uptake increased during the first hour after returning flow to control values, although mean arterial blood pressure, venous compliance, and total peripheral resistance were similar to the controls during the posthypotensive period. Three dogs were subjected to the same procedure, but without hypotension, to determine the influence of extracorporeal circulation on dynamic compliance when flow is constant. The results indicate that the dog on cardiopulmonary bypass responds to hypotension by arterial constriction and an increase in venous compliance. There was no evidence to indicate a loss of venous or arterial tone within 6 hours following the period of hypotension, although the gross changes in the gut at autopsy were similar to those seen in dogs dying in hemorrhagic shock.

Submitted on June 20, 1968
Accepted on June 11, 1969