Cerebral effects of cold reperfusion after hypothermic circulatory arrest

Objectives: This study was undertaken to explore whether an interval of col d reperfusion can improve cerebral outcome after prolonged hypothermic circ ulatory arrest, Methods: Sixteen pigs (27-30 kg) underwent 90 minutes of circulatory arrest at a brain temperature of 20 degreesC. Eight animals were rewarmed immedia tely after hypothermic circulatory arrest (controls), and X were reperfused for 20 minutes at 20 degreesC and then rewarmed (cold reperfusion). Electr ophysiologic recordings, fluorescent microsphere determinations of cerebral blood flow, calculations of cerebral oxygen consumption, and direct measur ements of intracranial pressure (millimeters of mercury) were obtained at b aseline (37 degreesC), before hypothermic circulatory an est, after discont inuing circulatory arrest at 37 degreesC deep brain temperature, and at 2, 4, and 6 hours thereafter. Histopathologic features and percent brain water were determined after the animals were sacrificed. Results: Cerebral blood flow and oxygen consumption decreased during coolin g: cerebral oxygen consumption returned to baseline levels after 4 hours, b ut cerebral blood flow remained depressed until 6 hours in both groups. Col d reperfusion failed to improve electrophysiologic recovery or to reduce br ain weight, but median intracranial pressure increased significantly less a fter cold reperfusion than in controls (P = .02). Although no significant d ifference in the incidence of histopathologic abnormalities between groups was found, all 3 animals with an intracranial pressure of more than 15 mm H g after immediate rewarming had histopathologic lesions, and high intracran ial pressure was more prevalent among all animals with subsequent histopath ologic lesions (P = .03). Conclusions: Cold reperfusion significantly inhibited the rise in intracran ial pressure seen in control pigs after 90 minutes of circulatory arrest at 20 degreesC, suggesting that cold reperfusion may decrease cerebral edema and thereby improve outcome after prolonged hypothermic circulatory arrest.