Fluid balance and blood volume measurement after aneurysmal subarachnoid hemorrhage

Background Patients with aneurysmal subarachnoid hemorrhage (SAH) are at risk for circulatory volume depletion, which is a risk factor for delayed cerebral ischemia (DCI). In a prospective observational study we assessed the effectiveness of fluid administration based on regular evaluation of the fluid balance in maintaining normovolemia. Methods A total of 50 patients with aneurysmal SAH were included and were treated according to a standard protocol aimed at maintaining normovolemia. Fluid intake was adjusted on the basis of the fluid balance, which was calculated at 6-h intervals. Circulating blood volume (CBV) was measured by means of pulse dye densitometry (PDD) on alternating days during the first 2 weeks after SAH. Results Of the 265 CBV measurements, 138 (52%) were in the normovolemic range of 60-80 ml/kg; 76 (29%) indicated hypovolemia with CBV < 60 ml/kg; and 51 (19%) indicated hypervolemia with CBV > 80 ml/kg. There was no association between CBV and daily fluid balance (regression coefficient beta = -0.32; 95% CI: -1.81 to 1.17) or between CBV and a cumulative fluid balance, adjusted for insensible loss through perspiration and respiration (beta = 0.20; 95% CI: -0.31 to 0.72). Conclusion Calculations of fluid balance do not provide adequate information on actual CBV after SAH, as measured by PDD. This raises doubt whether fluid management guided by fluid balances is effective in maintaining normovolemia.