Plasma colloid osmotic pressure during open-heart surgery using non-colloid or colloid priming solution in the extracorporeal circuit.

Two different priming solutions for the heart-lung machine were compared in 14 patients during aortic valve replacement. Colloid osmotic pressure (COP), and albumin in plasma, blood erythrocyte volume fraction (B-EVF) and arterial oxygen tension (PaO2) (FIO2 = 1.0) were followed before, during and after perfusion. The two priming solutions were 2,000 ml Ringerdex (7 patients) or 1,800 ml Ringerdex + 200 ml 20% albumin (7 patients). COP and B-EVF were normal before bypass. After 10 min on bypass, when about 1,000 ml of crystalloid cardioplegic solution had been given, COP was reduced by about 50% and B-EVF fell to 23%, indicating a small loss of water from the circulation when compared with in vitro dilution curves. COP was slightly lower in the non-colloid group (p less than 0.02). Both COP and B-EVF remained unchanged during perfusion, despite transfusion from the heart-lung machine of a mixture of blood and crystalloid solution with a calculated very low COP (6 mmHg) and B-EVF (15%). After perfusion the restitution of COP and B-EVF was rapid and parallel. Both returned to normal levels after 2 hours. There was a good correlation between COP and albumin measured in the same plasma samples (r = 0.83, p less than 0.001). At one hour after bypass PaO2 (FIO2 = 1.0) tended to decrease in the non-colloid group, compared with preperfusion level. 40 g of albumin was a too small amount of colloid to diminish substantially the reduction of COP during perfusion. The unchanged levels of COP and B-EVF during perfusion, despite further dilution as well as the parallel normalization after perfusion, can only be explained by loss of water from the circulation.