Hypoxic reperfusion after ischemia in swine does not improve acute brain recovery

We tested the hypothesis that transient hypoxic reperfusion after 15 min of global cerebral ischemia would improve acute recovery of electrical function. We also determined the changes in cerebral blood flow (CBF) and cerebral oxygen consumption (CMR(O₂)) during transient hypoxic reperfusion. Pentobarbital-anesthetized pigs were exposed to cerebral ischemia by raising intracranial pressure to 100 mmHg above arterial pressure with rapid infusion of artificial cerebral spinal fluid into a lateral ventricle. During the reperfusion period, normoxia was maintained at an arterial oxygen partial pressure (Pa(O₂)) of 80-120 mmHg for 120 min of reperfusion and hypoxia at a Pa(O₂) of 35-45 mmHg for the first 30 min of reperfusion in another group. The postischemic hypoxia group showed persistent elevation in microsphere- determined CBF at 30 min of reperfusion in all brain regions and lack of delayed hypoperfusion through 120 min of reperfusion. The normoxic group demonstrated transient postischemic hyperemia and hypoperfusion. CMR(O₂) was not significantly different between groups at any time point. In both groups, the somatosensory-evoked potential amplitude reached only 10% recovery by the end of 120 min of reperfusion. We conclude that hypoxemia during reperfusion after cerebral ischemia in this model does not improve acute brain electrical function and prolongs postischemic hyperemia.