Cerebral Metabolic Consequences of Hypotensive Challenges in Hemodiluted Pigs With and Without Cardiopulmonary Bypass

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Abstract
We tested the hypothesis that progressive aortic hypotension with bicarotid occlusion produces greater reductions in cerebral blood flow (CBF) and more flow-metabolism mismatching with hemodilution during cardiopulmonary bypass (CPB) than with hemodilution alone. In Yorkshire pigs randomized to hemodilution with CPB (n = 10) or hemodilution without CPB (control; n = 9), the effects of bicarotid ligation and graded hypotension on CBF (microspheres), the electroencephalogram (EEG), and cortical energy metabolites were examined. After bicarotid ligation, systemic flow was reduced for 15-min intervals of 80, 60, and 40 mm Hg aortic pressure, followed by a cortical brain biopsy. At baseline, CBF was lower in CPB (58 +/- 3 mL centered dot 100 g-1 centered dot min-1) than control (90 +/- 3 mL centered dot 100 g-1 centered dot min (-1); P < 0.05) animals, as was cerebral oxygen metabolism (3.1 +/- 0.1 vs 4.2 +/- 0.2 mL centered dot min-1 centered dot 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 metabolites were similar between CPB and control groups (adenosine triphosphate, 9.6 +/- 2.4 vs 12.4 +/- 1.9 micro mol/g; adenosine diphosphate, 6.0 +/- 0.7 vs 6.3 +/- 0.4 micro mol/g; adenosine monophosphate, 4.8 +/- 0.9 vs 3.8 +/- 0.8 micro mol/g; creatine phosphate, 8.3 +/- 1.8 vs 7.9 +/- 1.0 micro mol/g; and lactate, 178.4 +/- 20.2 vs 150.8 +/- 13.9 micro mol/g). Thus, despite significantly lower CBF during hypotension with bicarotid occlusion in hemodiluted animals during normothermic CPB, cortical electrical activity and the balance between flow and metabolism did not differ from those in control animals without CPB. (Anesth Analg 1995;81:911-8)