Correlation between cardiac output and cerebral blood flow following subarachnoid hemorrhage

The authors examined the correlations between cerebral blood flow (CBF) during the stage of vasospasm following subarachnoid hemorrhage and four parameters, namely, cardiac output (cardiac index), mean arterial blood pressure, age, and the Glasgow coma scale score. Forty-two patients who were diagnosed to have subarachnoid hemorrhage were included in this study, and 50 measurements were performed between day 5 and 12 following the subarachnoid hemorrhage. The CBF was measured by stable xenon-enhanced CT and the mean values of four CBF maps were corrected for a PaCO2 of 34 mm Hg (CBF34). The cardiac output and cardiac index were continuously monitored during the CBF measurement. The correlation coefficients of cardiac index, mean arterial blood pressure, age, and GCS against CBF34 were, respectively, 0.436, 0.227, 0.037, and 0.225, and the p values were, respectively, 0.002, 0.074, 0.789, and 0.087. The CBF34 was positively correlated with only the cardiac index and not with any of the other three parameters. Therefore, an increase in the cardiac output is apparently associated with an increase in the CBF during the stage of vasospasm following subarachnoid hemorrhage. Furthermore, we measured the CBF and cerebral perfusion pressure before and after increasing cardiac output in three patients during the stage of vasospasm. The CBF increased by 22.5% +/- 2.9 (SD), with a 42.0% +/- 16.4 increase in the cardiac index, however, no significant change in cerebral perfusion pressure was observed. Therefore, the increase in CBF associated with the increase in cardiac output seems to be attributable to a reduction in the cerebrovascular resistance.