Abstract
The relationship between residual cerebral blood flow and cerebral edema as well as hemorrhagic infarction seen following acute restoration of cerebral blood flow in an ischemic brain was experimentally studied. Dogs were divided into two groups with different mean arterial blood pressures (MABP) which were sustained at low levels by arterial exsanguination pretreatment: Group A with MABP of 40 mmHg and group B with MABP of 60 mmHg. The right middle cerebral artery (MCA) was occluded by an aneurysmal clip for one hour under these two hypotension levels. The occlusion was then released and MABP recovered towards normal levels.
In group A, MCA occlusion brought the local cerebral blood flow (1CBF) down to less than 8 ml/100 g/min. from 69 ml/100 g/min. Ten minutes after the release of MCA occlusion, the 1CBF increased to 109 ml/100 g/min. and was recognized as reactive hyperemia. Ninety minutes after the release, marked subarachnoid hemorrhage was seen in 5 out of 14 animals, and Evans Blue was extravasated into the cerebral tissue in one of three. Evidences of accumulation of water (85%) and sodium (555 mEq/kg), and decreases of potassium (395 mEq/kg) in the cerebral cortex were observed 6 hours after the release of MCA occlusion. The 1CBF in group B decreased to 20 ml/100 g/min. from 54 ml/100 g/min. after MCA occlusion. It regained its previous levels however, with or without mild reactive hyperemia after the release of the MCA occlusion. No subarachnoid hemorrhage or extravasation of Evans Blue or changes in the cerebral water and electrolyte contents were recognized.
When the residual cerebral blood flow is extremely limited, as in group A, the acute restoration of the blood flow by bypass surgery may be dangerous because of possible complications such as hemorrhagic infarction or severe edema, even if done within a short period after occlusion. The same procedure could, however, be performed without any complication if it is done within a short period after the onset of occlusion and if the residual cerebral blood flow of the ischemic area is maintained at a level of 20 ml/100 g/min. or approximately 37% of its previous level.
