Insulin binding to the cardiopulmonary bypass biomaterials

Hyperglycemia associated with cardiopulmonary bypass (CPB) is an independent predictor of morbidity and mortality. One suggested cause of hyperglycemia during CPB is a decline of serum insulin concentrations. Since plasma C-proteins are not reduced during CPB suggesting that pancreatic insulin secretion is not affected - the reduction of insulin concentrations is hypothesized to be due to the binding of the insulin protein to the CPB biomaterials. The hypothesis of this study is that insulin binds to the CPB polyvinyl chloride (PVC) tubing and that selected bio-coatings inhibit this process. Human insulin was diluted to a physiologic concentration of 30 mu U/mL in saline and exposed to four types of sterile PVC tubing, namely: uncoated, Terumo X-coated, Medtronic Carmeda, and Cobe SMARxT for 30 minutes at 37 degrees C. Insulin concentrations were determined with ELISA. The recovered insulin concentrations were found to be 9.3 +/- 0.6 mu U/mL in the uncoated (control), 17.7 +/- 1.9 mu U/ml, in the X-coating, 17.9 +/- 1.1 mu U/mL, in the Carmeda, and 14.28 +/- 0.17 mu U/mL in the SMAR(x)T coated tubing. These data support the hypothesis that the insulin binding to the PVC tubing can be reduced by 48% and up to 35% with X-coating and Carmeda, and SMAR(x)T coating, respectively. Therefore, the use of coated CPB systems is justified to reduce CPB-associated hyperglycemia.