Proteção cerebral durante parada circulatória total a 28°C

Abstract

Aortic surgical treatment of aneurysms is time dependent on the hypothermic circulatory arrest. Many techniques have been proposed to improve brain protection and increase safe time of ischemia (45 minutes in deep hypothermia). Brain protection during two hours of hypothermic circulatory arrest was studied in twenty-three animals that were divided in four groups. In the control groups, eight animals were submitted to anesthesia (group I) and extracorporeal circulation alone (group II). The other two groups underwent circulatory arrest associated with antegrade brain perfusion at 28°C (group III) and hypothermic circulatory arrest with retrograde brain perfusion at 28°C (group IV). Brain protection was evaluated by the histologic study and by the cellular brain metabolism which was studied by 31P Nuclear Magnetic Resonance spectroscopy. During circulatory arrest with antegrade brain perfusion at 28°C, the cellular metabolism remained normal during all the experiments and the brain structures were preserved. In the circulatory arrest with retrograde brain perfusion at 28°C, the intracellular brain pH, phosphocreatine (PCr) and adenosine triphosphate (ATP) decreased during the circulatory arrest period, and did not recover normal levels during reperfusion, the brain remained in severe intracellular acidosis. We conclude that during two hours of hypothermic circulatory arrest, antegrade perfusion at 28°C provides adequate brain protection. The hypothermic circulatory arrest associated with retrograde perfusion at 28°C does not protect the brain, from a metabolic and histologic point of view.