The cerebral circulatory response during canine anaphylactic shock.

Radiolabeled microspheres were employed to measure the cerebrovascular response to severe anaphylactic-induced hypotension in pentobarbital-anesthetized dogs. A rapid drop in mean arterial pressure (MAP, 140 to below 50 mm Hg) coincided with total and regional cerebral blood flows (CBF) that were not significantly different from prechallenge values. While blood flow to the occipital region (highest measured region of the brain) was significantly greater than that of brainstem regions prior to and during the shock regimen, no major redistributional phenomena occurred to any cerebral region. These findings were in contrast with other reports that demonstrated a loss in CBF and a redistribution of regional CBF as perfusion pressures declined below 55 to 60 mm Hg. To investigate whether the maintenance of CBF during severe anaphylactic hypotension was associated with cerebral hypoxia or hypercapnia, we employed in a second group of dogs the technique of venous drainage from the confluens sinus, so that the cerebral arterial-venous difference for blood gases and other blood components could be determined. Similar to our previous findings, CBF was maintained to perfusion pressures of 39 +/- 4 mm Hg. The drop in cerebral vascular resistance during the severe hypotensive period was not associated with a significant decline in arterial PO2, or a significant increase in arterial PCO2, A-V PO2, or V-A PCO2. Our results suggest that the fall in cerebral vascular resistance during anaphylactic-induced hypotension would not be associated with a severely altered cerebral metabolism.