Intracerebral Blood Flow Distribution during Hypotensive Anesthesia in the Goat

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Abstract
The effects of hypotension (40-50 torr range) as induced by inhalation of halothane (2-3%), halothane (0.75%) plus sodium nitroprusside (0.2-0.4 mg/kg per min) or halothane (0.75%) plus trimethaphan (4-16 mg/kg per min) on total and regional cerebral blood flow (tCBF, rCBF) in the goat were measured by radioactive microsphere distribution technique. Inhalation of halothane (2-3%) alone caused an average reduction in tCBF of 25%, with no significant reduction in regional flow except in cortical white matter, which showed a 42% reduction. Halothane with sodium nitroprusside infusion caused an average 45% decrease in tCBF and significant decreases in blood flows to the thalamus (42%), cerebellum (41%), cortical gray matter (35%) and white matter (58%). Halothane with trimethaphan infusion produced a reduction in tCBF (47%), associated with a significant decrease in blood flows to the thalamus (36%), cerebellum (41%), cortical gray matter (22%) and white matter (47%). Both halothane with sodium nitroprusside and halothane with trimethaphan produced significantly greater reductions of blood flows to the thalamus, cerebellum and gray and white matter than did 2-3% halothane. Both caused significantly greater reductions in tCBF than did 2-3% halothane. Of all brain regions studied, only the hypophysis showed no statistically significant reduction in rCBF no matter which technique was used to produce hypotension. Cortical white matter appeared to be the region most affected by each technique.