CEREBRAL METABOLIC CONSEQUENCES OF HYPOTENSIVE CHALLENGES IN HEMODILUTED PIGS WITH AND WITHOUT CARDIOPULMONARY BYPASS

We tested the hypothesis that progressive aortic hypotension with bica rotid occlusion produces greater reductions in cerebral blood flow (CB F) and more flow-metabolism mismatching with hemodilution during cardi opulmonary bypass (CPB) than with hemodilution alone. In Yorkshire pig s randomized to hemodilution with CPB (n = 10) or hemodilution without CPB (control; n = 9), the effects of bicarotid ligation and graded hy potension on CBF (microspheres), the electroencephalogram (EEG), and c ortical energy metabolites were examined. After bicarotid ligation, sy stemic flow was reduced for 15-min intervals of 80, 60, and 40 mm Hg a ortic pressure, followed by a cortical brain biopsy. At baseline, CBF was lower in CPB (58 +/- 3 mL . 100 g(-1). min(-1)) than control (90 /- 3 mL . 100 g(-1). min(-1); P < 0.05) animals, as was cerebral oxyge n metabolism (3.1 +/- 0.1 vs 4.2 +/- 0.2 mL . min(-1). 100 g(-1); P < 0.05). Although CBF remained 40% lower at each level of hypotension in CPB than control animals (P < 0.05), EEG scores showed no intergroup differences, indicating Similar flow-metabolism matching. Brain metabo lites were similar between CPB and control groups (adenosine triphosph ate, 9.6 +/- 2.4 vs 12.4 +/- 1.9,mu mol/g; adenosine diphosphate, 6.0 +/- 0.7 vs 6.3 +/- 0.4 mu mol/g; adenosine monophosphate, 4.8 +/- 0.9 vs 3.8 +/- 0.8 mu mol/g; creatine phosphate, 8.3 +/- 1.8 vs 7.9 +/- 1. 0 mu mol/g; and lactate, 178.4 +/- 20.2 vs 150.8 +/- 13.9 mu mol/g). T hus, despite significantly lower CBF during hypotension with bicarotid occlusion in hemodiluted animals during normothermic CPB, cortical el ectrical activity and the balance between flow and :metabolism did not differ from those in control animals without CPB.