Relationship between residual cerebral blood flow and oxygen metabolism aspredictive of ischemic tissue viability: sequential multitracer positron emission tomography scanning of middle cerebral artery occlusion during the critical first 6 hours after stroke in pigs

Object. The authors rested the hypothesis that oxygen metabolism is the key factor linking the long-term viability of ischemic brain tissue to the mag nitude of residual blood flow during the first 6 hours following a stroke. Methods. Eleven anesthetized pigs underwent a series of positron emission t omography studies to measure cerebral blood flow (CBF) and metabolism befor e and for 7 hours after the animals were subjected to permanent middle cere bral artery (MCA) occlusion. The extent of collateral blood supply was asse ssed using angiography. Abnormal metabolism of the ischemic tissue progress ed as a function of time in inverse proportion to the magnitude of residual CBF, and the volume of the infarct grew in inverse proportion to the resid ual blood supply. Ten hours after occlusion of the MCA, the infarct topogra phically matched the tissue with a cerebral metabolic rate of oxygen consum ption below 50% of values measured on the contralateral side. This was also the threshold for the decline of the oxygen extraction fraction below norm al, which was critical for the prediction of nonviable ischemic tissue. Mil dly ischemic tissue (CBF > 30 ml/100 g/min) did not reach the cerebral meta bolic rate of oxygen threshold of viability during the first 6 hours after MCA occlusion; moderately ischemic tissue (CBF 12-30 ml/100 g/min) reached the threshold of viability in 3 hours; and severely ischemic tissue (CBF < 12 ml/100 g/min) remained viable for less than 1 hour. Conclusions. The relationship between the residual CBF and both oxygen meta bolism and extraction is critical to the evolution of metabolic deficiency and lesion size after stroke.