In Vitro Heparin-Protamine Dosing

Introduction: In cardiac surgical patients, heparine (HEP) and protamine (PROT) are commonly dosed according to patient's weight and their effects are monitored with the activated coagulation time (ACT). However, it is well known that patients have different sensitivities to these drugs and that the ACT is affected by many factors (hemodilution, hypothermia) [1], reducing its accuracy and reliability. The Hepcon HMS is a monitoring device that measures in vitro the patient's sensitivity to HEP and monitors ACT along with HEP concentration [HEP] during cardiopulmonary bypass (CPB). PROT is administered according to the final [HEP] obtained. Despotis has shown that this method of anticoagulant dosing and monitoring reduced the need for allogenic blood products (ABP). [2] Antifibrinolytics (AF) or pre-op heparinized blood sequestration (HBS) were not permitted. This study was designed to compare a weight based anticoagulation method versus the Hepcon-HMS method on blood loss and ABP use in cardiac surgical patients otherwise exposed to usual blood conservation therapy (AF, HBS and Cell-Saver (CS)). Methods: After informed consent, 50 patients were randomized to Control group (CG) or Study group (SG). In CG, 300 u/kg of HEP were given as initial bolus, 5000 u were added to the pump prime (PP) and 5000-10000 u added as necessary to maintain ACT above 480. PROT was calculated in the following manner: 1 mg of PROT/100 u of HEP (initial HEP bolus + HEP in PP) + 20 mg. In SG, the initial HEP bolus was given according to a in vitro heparin dose response test and a baseline [HEP] was measured. 5000 u of HEP were also added in the PP. During CPB, the ACT and [HEP] were maintained above 480 sec and baseline [HEP] respectively. After CPB, PROT was given according to the last [HEP] measured. Results: One patient was excluded in each group because they returned in OR for hemostasis. There were no differences in demographic data and an equal number of patients in each group were exposed to AF, HBS and CS. There were no statistical differences in post-op chest tube drainage nor blood products usage. Table 1Table 1Discussion: These data indicate that the above apparatus and method for HEP and PROT dosing and monitoring offers no benifit on blood loss or ABP use compared to a weight based anticoagulation method in cardiac surgical patients exposed to usual blood conservation therapy. Furthermore, the Hepcon HMS system is more costly and time consuming.