Depression of circulating blood volume in patients after subarachnoid hemorrhage: implications for the management of symptomatic vasospasm.

The result of 42 blood volume determinations made with autologous red blood cells labeled with chromium-51 are reported. The subjects consisted of 11 control patients and 25 patients with recent subarachnoid hemorrhage (SAH). The mean red blood cell volume (RBCV) and the total blood volume (TBV) for female patients after SAH were significantly lower than corresponding control values (P less than 0.01). No depression of blood volume was found in males as a group. Seventy-two per cent of females had below-normal RBCV and 50% had below-normal TBV. Fifteen patients demonstrated angiographic vasospasm or signs of cerebral ischemia. Only 1 patient with asymptomatic vasospasm had a below-normal RBCV or TBV, whereas 6 of 7 patients with symptomatic vasospasm had a subnormal RBCV or TBV. The mean RBCV and mean TBV for female patients with symptomatic vasospasm were significantly lower than corresponding control values (P less than 0.02) and lower than values for female patients with asymptomatic vasospasm (P less than 0.05). The data suggest that volume status may be the important differential between asymptomatic and symptomatic vasospasm. Delayed ischemic deficits can be expected to develop in patients who have both spasm of the intracranial vessels and decreased TBV. Patients with normal blood volume are far less likely to experience cerebral ischemia, even if vasospasm develops.