Protamine in Cardiac Surgery and Haemostasis

Protamine is used after Cardiopulmonary Bypass (CPB) to reverse the anticoagulant effects of heparin and restore coagulation. Convincing evidence from in-vitro and in-vivo studies suggest that an overdose of protamine has anticoagulant effects which might lead to bleeding complications. Heparin levels usually decrease during cardiac surgery with CPB. Therefore, a protamine regimen based on the initial heparin dose before CPB might lead to overdose of protamine. In contrast, a protamine regimen based on the actual heparin concentration may avoid this condition. The investigators compare both regimens of protamine dosing in patients undergoing complex surgery with CPB and assess its effect on the amount of protamine given, markers of the coagulation system, utilization of blood products and perioperative blood loss.

Before induction of anesthesia, patients are randomized to the two different dosing regimen for protamine. Both, the anesthetist and the surgeon were blinded regarding the grouping of the patients.

Anesthesia and CPB

Anesthesia is performed as a balanced anesthesia with a bolus of fentanyl, etomidate, pancuronium-bromide followed by a continuous infusion of remifentanil and vaporization of sevoflurane. Additionally, in all patients a continuous infusion of 0.25 µg/kg/min milrinone will be started after induction of anesthesia. Further inotropic or vasoactive agents (Dobutamine 3-5 µg/kg/min; epinephrine 0.05-0.2 µg(kg/min, norepinephrine 0.05-0.2 µg/kg/min) will be only given when a target cardiac index of \< 2.2 l/m² BSA and mean arterial pressure of \>70 mmHg is not achieved with this therapy.

In order to compensate the degree of hemodilution due to differences in weight, in patients with a body surface area (BSA) of \<1.8 m², a CPB system with a priming volume of 1100 ml will be used while in patients with a BSA of \>1.8m² a system with a priming volume of 1500 ml was employed. CBP will be performed with open non-coated CPB circuits in mild hypothermia with a core temperature of 32-34°C. Cardioplegia will be achieved using warm blood cardioplegia according to Calafiore.

All patients receive tranexamic acid (TA) with a bolus of 1 g to the patient, 0.5 g added to the CPB volume and a continuous infusion of 0.2 g/hour during CPB.

Heparin and Protamine Management

Heparin will be given with a bolus of 400 IU/kg to achieve a target celite ACT (Actalyke ACT, Helena Lab. Beaumont, TX USA) value of \>450 seconds. If this target is not reached, additional boluses of 1/3 rd of the first dose will be given until prolongation to the target value is achieved. Additional 10.000 units of heparin will be given into the priming volume of the CPB circuit.

Heparin concentrations were measured five minutes after beginning of CPB using the white (range 3.4-6.8 IU/ml heparin) heparin protamine titration (HPT) cartridge of the Hepcon HMS Plus™ device (Medtronic INC, Minneapolis, Min, USA) and shortly after termination of CPB using the golden HPT cartridge (range 2.0 - 5.4 IU/ml heparin).

The total protamine dose consists of 100 ml. Of this 80 ml will be given as a short infusion over 10 min. directly after termination of CPB. The remaining 20 ml will be given when the residual CPB blood is re-infused into the patient after arterial decannulation, which will be performed 10-15 minutes after weaning from CPB.

In the weight based protamine group (Group 1, the total amount of protamine will be calculated 1:1 according to the initial heparin dose necessary to achieve the target ACT of \>450 sec. In the heparin level based group, the total protamine amount will be calculated 1:1 according to the actual heparin level measured after termination of CPB with the use of Hepcon HMS Plus™ device.

Coagulation Tests

Fifteen minutes after infusion of protamine, the INTEM, FIBTEM and HEPTEM test will be performed on the ROTEM thromboelastometry system (TEM International GmbH, Munich Germany). In all tests, the coagulation time (CT) reflects the period until clot formation starts; the clot formation time (CFT) reflects the period until a clot strength of 20 mm is achieved and the maximal clot firmness MCF)reflects the maximal clot strength. In the INTEM test the intrinsic coagulation pathway is activated.

Transfusion triggers

During CPB the critical hemoglobin (Hb) triggering transfusion of packed red blood cells (PRBC) is defined at 8 g/dl. After CPB, in patients with a CI \>2.2 l/m² the critical value is at \>8-9 g/dl, while in patients needing further medical support with dobutamine/epinephrine or norepinephrine the minimum target was defined at \>9-10 g/dl.

In patients with diffuse bleeding after protamine administration, therapy with fresh frozen plasma (FFP), prothrombin complex concentrate (Beriplex, CSL Behring, Marburg, Ger) , fibrinogen concentrate (Haemocomplettan P®, CSL Behring, Marburg, Germany) and single donor aphaeresis platelet concentrates will be based on the results of the ROTEM analysis. However, these blood products will only be given when diffuse microvascular bleeding is observed in the operation field.

In case of a moderate prolongation of the CT (240-360 sec) in the INTEM test (and comparable result in the HEPTEM test) 3-4 units of FFP will be transfused. If bleeding persists, additional 3-4 units of FFP or in case of a prolongation of the CT\>360 sec. 2000-4000 IU of prothrombin complex concentrate will be given.In case of an MCF \< 45 mm to platelet concentrates will be transfused.

Eligibility Criteria:
Inclusion Criteria:

* Primary surgery
* Preoperative hemoglobin value \< 12 g/l
* Preoperative platelet count \< 200 c/µl
* Patients with a body weight \< 50 kg
* No known defect of the coagulation system
* Normal pre-operative ROTEM values of the INTEM and FIBTEM
* Patients with unimpaired renal function (creatinine clearance \< 30 ml/kg/min)

Exclusion Criteria:

* \<18 years
* No informed consent
* Re-do surgery
* Known defect of the coagulation system
* Renal impairment