A novel method for the direct determination of heparin concentration during cardiopulmonary bypass surgery

Heparin is the standard drug for anticoagulation treatment and is used in many cardiac surgical interventions to prevent blood clotting. The anticoagulation status is controlled by various clotting tests. However, these tests depend on parameters like temperature, hemodilution etc. and are thus not applicable for a direct monitoring of the heparin concentration. The aim of this prospective study was to test a novel light scattering assay (LiSA) for the direct determination of heparin concentration during cardiopulmonary bypass (CPB) surgery and to compare the heparin concentrations with routinely determined activated clotting time (ACT).

The patient group consisted of 50 patients undergoing coronary bypass surgery with CPB. The coagulation status was monitored by the measurement of ACT, which was performed approximately every 30 min during surgery. Parallel to each ACT measurement, the heparin concentration was measured by LiSA.

For 70% of the patients, ACT and heparin concentration measured by LiSA correlated reasonably over the entire time course of the intervention. For 30% of the patients, an insufficient correlation or even no correlation at all was observed.

This study showed that LiSA enables the determination of intra-operative heparin levels. The lack of correlation between ACT and heparin concentration in a substantial group of patients shows that monitoring of heparin concentration is important. A more precise blood coagulation management, in particular, a precise administration of heparin and protamine, should be based on a combination of the measurement of heparin concentration and of ACT, but not on ACT alone.