Preservation of blood volume during edema removal in nephrotic subjects

During the gradual removal of edema with diuretics in 21 edematous patients with the nephrotic syndrome (NS) we monitored blood volume. For comparison, nine healthy subjects were studied after equilibration on diets containing 20, 200, and 1138 mEq sodium. The initial extracellular fluid volume (ECFV) in the patients exceeded the final ECFV by 63.4 +/- 8.4%. In 10 patients with a very low plasma oncotic pressure (8.2 +/- 0.4 mm Hg, Group 1), the blood volume changed little. In Group 2 (plasma oncotic pressure 13.4 +/- 1.0 mm Hg), it was 11.0 +/- 2.5% higher at entry than after edema withdrawal. In the normal volunteers, the highest sodium intake raised the ECFV by 21.4 +/- 4.1%. The accompanying rise in blood volume, 11.2 +/- 3.0%, was larger than in the patients of Group 1 (2.4 +/- 1.9%, P less than 0.04), but not of Group 2 (8.1 +/- 1.9%, NS) at similar degrees of expansion. There was no difference in blood volume between the edema-free patients and the normal subjects at low-sodium diet. The course of blood pressure and creatinine clearance during edema removal gave no evidence that functional hypovolemia was induced, but the plasma renin activity was higher than in the normal subjects at similar degrees of expansion. We conclude that the blood volume to ECFV relationship curve is flattened in the presence of hypoalbuminemia. Thus, the increase in blood volume that normally follows ECFV expansion is less in patients with the NS, but a drop below normal upon removal of edema is absent also.