Cerebral metabolic consequences of hypotensive challenges in hemodiluted pigs with and without cardiopulmonary bypass

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 · 100 g^-1 · min^-1) than control (90 ± 3 mL · 100 g^-1 · min^{- 1}; P < 0.05) animals, as was cerebral oxygen 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 metabolites were similar between CPB and control groups (adenosine triphosphate, 9.6 ± 2.4 vs 12.4 ± 1.9 μmol/g; adenosine diphosphate, 6.0 ± 0.7 vs 6.3 ± 0.4 μmol/g; adenosine monophosphate, 4.8 ± 0.9 vs 3.8 ± 0.8 μmol/g; creatine phosphate, 8.3 ± 1.8 vs 7.9 ± 1.0 μmol/g; and lactate, 178.4 ± 20.2 vs 150.8 ± 13.9 μmol/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.