Free water clearance after supplemental albumin resuscitation for shock

Previous studies have shown that albumin supplementation in the resuscitation of hypovolemic shock impairs sodium and water excretion and increases renal insufficiency by mechanisms not fully delineated. Free water clearance (CH2O) is a sensitive indicator of renal tubular function. This study further investigates the renal effects of albumin by analyzing CH2O in 94 patients who received an average of 14.5 transfusions for shock; 46 received 31 g of albumin during operation and up to 150 g/day postoperatively while 48 received only electrolyte solution. Patients treated with albumin had a significant decrease in sodium clearance (CNa) (1.4 vs. 2.4 ml/min); however, they were more likely to have an abnormal increased CH2O (greater than 0.25 ml/min) (41% vs. 19%) or near zero CH2O (+/- 0.25 ml/min) (11% vs. 8%) than a normal negative CH2O (less than -0.25 ml/min) (48% vs. 73%). Peritubular albumin concentration correlated inversely with sodium excretion (ENa) and plasma volume correlated positively with ENa, but neither correlated with CH2O. However, filtered Na+ load correlated positively with both CNa and ENa and inversely with CH2O. Therefore, the combination of decreased CNa and increased CH2O reflects 1) increased peritubular oncotic pressure leading to greatly increased Na+ and water reabsorption, 2) increased plasma volume leading to decreased reabsorption of both, and 3) decreased filtered Na+ load causing a selective increase in Na+ reabsorption. These changes are mediated through distal nephron sodium-potassium exchange and result in increased CH2O after albumin therapy.