Systemic hypovolemia after subarachnoid hemorrhage

Two patients who had suffered subrachnoid hemorrhage were subjected to intensive monitoring of parameters of circulating blood flow, cardiovascular dynamics, and fluid and electrolyte balance. Among the parameters studied were red cell volume, plasma volume, and total blood volume, cardiac output, and central venous and pulmonary capillary wedge pressures. Both patients experienced acute neurological deterioration during the study. Red cell volume fell in a premonitory fashion prior to neurological deterioration in both, and in one patient plasma volume and total blood volume decreased by almost 50% in the 5 days prior to neurological deterioration. Central venous and pulmonary capillary wedge pressures fell initially but did not predict the deterioration. Systemic vascular resistance fell prior to clinical deterioration in one patient following ventriculoperitoneal shunting, and in the other following craniotomy and subarachnoid drainage. The falls in systemic vascular resistance may have caused shunting of cardiac output away from the compromised cerebral circulation, thereby triggering neurological deterioration.