Extracranial-intracranial bypass surgery: hemodynamic and metabolic effects.

After superficial temporal artery-middle cerebral artery bypass, cerebral blood flow (CBF) in the operated hemisphere increased in 6 of 17 patients. Preoperatively, the symptomatic hemisphere showed lower CBF in all six, lower oxygen metabolism in five, higher blood volume in four, and higher oxygen extraction in two. With the postoperative increase in hemispheric CBF, there was a decrease in oxygen extraction, but no change in blood volume or oxygen metabolism. In these patients, chronic regional hypoperfusion followed major vascular occlusion. Compensatory responses included dilation of intraparenchymal vessels and increased transport of oxygen from blood to tissue. These changes were partially reversed by cerebral revascularization.