The influence of halothane and nitroprusside on canine spinal cord hemodynamics.

Regional spinal cord blood flow was measured in 12 halothane-anesthetized mongrel dogs by means of 15 +/- 3 u radiolabeled microspheres under (1) control conditions, (2) 60-torr mean arterial blood pressure (MAP) using sodium nitroprusside (NPS), (3) 50-torr MAP using NPS, and (4) after reestablishment of normotension. With the onset of either level of hypotension, there were nonsignificant decreases from control conditions in cardiac output and pulmonary capillary wedge pressure (PCWP). A rise in heart rate was seen at 50 torr MAP. There were no significant changes in spinal cord blood flow (SCBF) under either hypotensive condition in any region of the cord, indicating an intact autoregulatory response. Sensitivity of SCBF to changes in the PaCO2 was shown to be 1.02 ml/min/100 g tissue per torr PaCO2. These data showed that (1) deliberate hypotension with NPS did not change SCBF in the dog; (2) sensitivity to PaCO2 was high under halothane anesthesia; and (3) SCBF was relatively homogeneous throughout the length of the cord.