CEREBROVASCULAR EFFECTS OF HIGH INTRACRANIAL-PRESSURE AFTER MODERATE HEMORRHAGE

Patients with head injuries often develop increased intracranial press ure after hemorrhage. The authors studied the effect of moderate hemor rhage followed by elevated intracranial pressure on cerebrovascular va riables. Cerebral blood flow in la pigs was measured with laser Dopple r flowmetry, and cerebral venous blood gases were taken from the sagit tal sinus. High intracranial pressure (80% of mean arterial pressure) was induced by infusion of artificial cerebrospinal fluid into the cis terna magna, and blood pressure was reduced by bleeding to a mean of 7 8% of the prebleeding values in eight pigs. Five pigs served as second ary controls. High intracranial pressure before hemorrhage caused a de crease in cerebral blood flow to 34% of the baseline values, a decreas e in sagittal sinus oxygen saturation to 46%, and a decrease in cerebr al perfusion pressure to 36%, but did not change cerebrovascular resis tance. High intracranial pressure after hemorrhage decreased cerebral blood flow to 14% of baseline values. Sagittal sinus oxygen saturation decreased to 22%, cerebral perfusion pressure decreased to 30%, and t he cerebrovascular resistance increased by 355%. The moderate hypotens ion after hemorrhage caused a considerable enhancement of the effects of high intracranial pressure on cerebral hemodynamics.