PHENYLEPHRINE DOES NOT REDUCE CEREBRAL PERFUSION DURING CANINE CARDIOPULMONARY BYPASS

Gaseous microemboli during cardiopulmonary bypass (CPB) could injure t he blood-brain barrier so that cerebral vasoconstriction would result from infusing alpha-agonist drugs, such as phenylephrine. Cerebral blo od flow (radioactive microspheres) and metabolism were measured in sev en dogs after rewarming from 150 min hypothermic CPB with bubble oxyge nators used to produce gaseous microemboli. Phenylephrine (40 mu g/min ) was infused directly into the brachiocephalic artery so that aortic pressure before (80 +/- 2 mm Hg) and during (79 +/- 3 mm Hg) the infus ion did not change. Neither blood flow to the cerebral hemispheres (P = 0.960), cerebellum (P = 0.854), and brainstem (P = 0.694) nor the ce rebral metabolic rate for oxygen (P = 0.862) differed when values obta ined before and after 30 min of phenylephrine infusion were compared. Cerebral vascular resistance was also unchanged by phenylephrine, bein g 1.22 +/- 0.10 mm Hg . mL(-1) . min(-1) . 100 g(-1) before infusion a nd 1.25 +/- 0.17 mm Hg . mL(-1) . min(-1) . 100 g(-1) during infusion (P = 0.849). Phenylephrine does not cause cerebral vasoconstriction af ter rewarming from hypothermic CPB, a finding which suggests that the blood-brain barrier is preserved during bypass.