Canine Systemic and Cerebral Effects of Hypotension Induced by Hemorrhage, Trimethaphan, Halothane, or Nitroprusside

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Abstract
In 62 dogs, hypotension to a mean arterial pressure of either 40 or 50 torr (equivalent to a cerebral perfusion pressure of 30 or 40 torr, respectively) for 1 h was induced by hemorrhage (oligemia), trimethaphan, halothane or sodium nitroprusside. Before and during the period of hypotension, the following were measured: mean arterial blood pressure, cardiac output, whole-body O2 consumption, cerebral blood flow, cerebral O2 consumption, arterial blood gases, blood O2 content, and lactate, pyruvate, glucose, epinephrine and norepinephrine concentrations. At the end of the period of hypotension, brain biopsies were taken for determination of ATP, phosphocreatine, lactate and pyruvate concentrations. In an additional 8 dogs following 1 h of hypotension (at 40 torr) induced by 1 of the 4 techniques, the brains were perfused with carbon black, removed, and examined. In another 10 dogs following hypotension (at 40 torr) induced with either halothane or trimethaphan, the animals were observed for 3 days and then killed for examination of the brain. Dogs maintained at a mean arterial pressure of 40 torr, despite differences in cerebral blood flow, demonstrated metabolic disturbances compatible with systemic and cerebral hypoxia. These were greatest in those dogs given nitroprusside in excess of 1.0 mg/kg, presumably due to cyanide toxicity. In dogs maintained at 50 torr, metabolic disturbances were minimal or absent in the halothane- and nitroprusside-treated dogs but were still apparent in the oligemic and trimethaphan-treated dogs. Carbon black infusions revealed no evidence of nonhomogeneous flow. Three of the 10 dogs observed for 3 days had persistent post-hypotension neurologic dysfunction. Two of these were given trimethaphan. The systemic and cerebral effects of halothane and nitroprusside (at doses < 1.0 mg/kg) were similar and at a mean arterial pressure of 50 torr were of little consequence. Hypotension induced by trimethaphan or oligemia resulted in detectable metabolic alterations even at a pressure of 50 torr.

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