Influence of intravascular albumin on the capillary leakage of fluid in humans

BACKGROUND: The Starling equation gives intravascular albumin a unique role in controlling capillary filtration and urine flow. The present study evaluated the strength by which this role is executed, in addition to other factors that statistically influence the capillary leakage and urine flow rates. METHODS: The capillary filtration and the urine flow were estimated by volume kinetic analysis at 2992 time points during 158 intravenous infusion experiments in volunteers and surgical patients who received 25 mL/kg of Ringer solution or 3 mL/kg of 20% albumin. Stepwise multiple regression was used to compare these estimates to a set of perioperative variables. RESULTS: The infusions of Ringer diluted plasma albumin by 5 g/L while 20% albumin increased the same concentration by 6 g/L, and this difference had a profound influence on the studied variables. Despite similar plasma volume expansion (13 versus 11%), the capillary filtration was 10 times higher during the Ringer experiments than during the albumin experiments, and the urine flow was twice as high. Bleeding reduced both flow variables, whereas ongoing surgery accelerated the filtration, but inflammation decreased it, and a high arterial pressure increased the urine flow. Regression analysis predicted 80% of the capillary filtration but only 21% of the urine flow. CONCLUSION: Marked changes in the capillary leakage rate occur when diluting or deliberately increasing the plasma albumin concentration. Similar effects apply to the urine flow, but this rate is governed by a more complex set of variables.