Intracerebral blood flow distribution during hypotensive anesthesia in the goat

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