Serial measurements of CBF using 133Xe inhalation technique and cerebral oxygen metabolism were carried out in patients who were treated postoperatively with hypervolemic hemodilution therapy. Patients with cerebral vasaspasm showed significant reduction of CBF and cerebral delivery of oxygen (D-O2) and an elevation of oxygen extraction fraction (OEF). Significant reductions of cerebral metebolic rate of oxygen (CMRO2) were not observed in patients with non-symptomatic vasospasm due to the elevation of OEF. In patients with symptomatic vasospasm, marked reductions of D-O2 were followed by significant reductions of CMRO2 in spite of the elevation of OEF. A critical CBF level of about 25ml/100g/min (45% of normal value) was noted in patients who developed neurological symptoms with LDAs on CT scan.
Influence of hematocrit (Ht) values on D-02 was evaluated in 24 cases including 4 patients with cerebral ischemic attack due to cerebral vasospasm, and optimal Ht value (X) and maximal D-O22 (Y) were calculated in each cases. There was a close correlation between X values and Y values (r=0.91). This data suggest that D-O22 in normal subjects becomes maximum in condition of a Ht value of about 40-45%, however, when D-O22 reduces in a half value of normal condition in patients with cerebral vasospasm and cerebral ischemia, maximal D-O22 is expected in condition of a Ht value of about 27-30% (Hemodilution).
These results indicate that hypervolemic hemodilution therapy improves only cerebral perfusion but cerebral oxygenation during the period of cerebral vasospasm.
