Estimation of Colloid Osmotic Pressure During Hemodilutional Cardiopulmonary Bypass

Patients undergoing cardiopulmonary bypass (CPB) using hemodilution are subjected to large reductions in colloid osmotic pressure (COP). The purpose of this investigation was to determine the course of COP during CPB and to compare these values to critical ranges for COP as cited in the literature. The prime consisted of a mixture of the crystalloid (Lactated Ringer’s) and a variety of colloids. Samples were taken of the prime, and blood drawn prior to, during, and after CPB. The COP of each sample was measured, and also estimated by three (3) different techniques. During CPB, patient’s COP were reduced by 30–60%, placing them within the published critical ranges for COP. Since patients did not suffer the predicted consequences of large reductions in COP, it is apparent the previously accepted critical ranges for COP must be re-evaluated for the CPB patient. In the process of this investigation, a simple pumpside method for COP estimations was developed.