COLLOID OSMOTIC-PRESSURE OF PLASMA REPLACEMENT FLUIDS

Colloid osmotic pressure (COP) of some of the most frequently used pla sma replacement fluids was measured with a colloid osmometer. COP of 4 % human albumin solutions was only half that of normal human serum (13 .6 +/- 0.6 vs. 27.5 +/- 2.7 mmHg (1.8 +/- 0.1 vs. 3.7 +/- 0.4 kPa)) (m ean +/- s.d.), whereas COP of 20% human albumin solutions was eight ti mes higher (196.0 +/- 12.3 mmHg (26.1 +/- 1.6 kPa)). Enhancing the pro tein concentration from 4% to 20% in the human albumin solutions incre ased COP 14-fold, reflecting the exponential relationship between prot ein concentration and COP of a solution. Fresh donor plasma furnished by the hospital blood-bank had a COP about 30% below normal human seru m (18.1 +/- 1.3 mmHg (2.4 +/- 0.2 kPa)), due to dilution during prepar ation. Dextran 70 (6%) had a COP more than twice, and Ringer-Dextran 6 0 (3%) about 75% of that of normal human serum. Dextran 40 (10%) and g elatin (3.5%), Haemaccel) leaked markedly through the membrane of the colloid osmometer, making acceptable measurements impossible. Seven di fferent hydroxyethyl starch (HES solutions were measured, and the COP varied between half and 3 times that of normal human serum, depending on molecular weight and concentration of the HES.