RESUMO
OBJECTIVE: To investigate if a mean arterial pressure below 50 mmHg during CPB may lead to cerebral ischemia. MATERIAL AND METHODS: Piglets with low mean arterial pressure by nitroprusside (LP-group) (n=6) were compared with piglets given norepinephrine to obtain high pressure (HP-group) (n=6) during normothermic and hypothermic CPB. Intracranial pressure, flow and markers of cerebral energy metabolism (microdialysis) were recorded. RESULTS: Mean arterial pressure differed significantly between the groups and stabilized about 40-45 mmHg in the LP-group. Cerebral perfusion pressure decreased to 21.3 (7.7) mmHg in the LP-group and increased to 51.8 (11.2) mmHg in the HP-group at 150 min of CPB (P<0.001, between groups). During bypass the intracerebral glucose concentration decreased significantly in the LP-group. In this group the lactate/pyruvate ratio increased from 15.5 (5.3) to 64.5 (87.6) at 90 min and 45.0 (36.5) at 150 min (P<0.05) with no such changes in the HP-group. Similarly the cerebral glycerol concentration increased significantly in the LP-group, whereas glycerol remained stable in the HP-group. CONCLUSION: Mean arterial pressure about 40 mmHg during CPB is associated with cerebral ischemia.
