Method:
A retrospective cohort study was conducted including seven hundred and two patients who underwent elective or urgent CABG in our unit between April 2014 and January 2017. Those who underwent emergent CABG were excluded from the study due to their intricate higher bleeding risk from other factors.
All patients included within the study were managed using our unit’s standard operating protocols. Preoperatively aspirin was held 5 days pre-operatively except in those with high-risk coronary anatomy (significant left main-stem (LMS) disease or LMS equivalent). Clopidogrel was held for 5 days and ticagrelor for 3. With regards to other anticoagulants warfarin was held for 5 days with a preoperative INR check performed 1 day prior to surgery. Direct oral anticoagulants were held for 3 days and low molecular weight heparin was held the night before surgery. For those patients requiring a preoperative heparin infusion this was held a minimum of 6 hours pre-operatively.
Intraoperatively a baseline activated clotting time (ACT) was taken prior to heparin administration. 300 mg/kg (measured body weight) of heparin was administered in all patients. Cardiopulmonary bypass was established with a minimum ACT of 480 seconds, between aortic and dual-stage right atrial cannula used for commencing cardiopulmonary bypass. After weaning from cardiopulmonary bypass protamine was administered via a standardised protocol based on the previous ACT measurement with a final ACT taken after administration to ensure return to baseline.
Postoperatively all patients were transferred to our intensive care unit. Colloid and packed red cells were infused as per protocol with a transfusion threshold of haemoglobin under 80 grams/litre used. Mediastinal and pleural drainage were monitored hourly and any deviation from standard prompted the running of thromboelastogram (TEG) testing and targeted fresh-frozen plasma, platelet and cryoprecipitate transfusion. In those not receiving a protamine infusion an extra bolus of protamine (25-50mg) was given in those with significant pre- and post-heparinase values.
Mixed practice exists between surgeons within our unit with some preferring the routine use of a postoperative protamine infusion in intensive care and some not. Our postoperative protamine infusion has been standardised for those who did receive it, consisting of 100mg protamine mixed in 100ml 0.9% saline given over 4 hours intravenously. This was started on arrival in the intensive care unit.
Demographics along with outcome data were collected from our CVIS database. Outcome measures assessed were; post-operative mediastinal and pleural drainage for the first 24 hours (this was indexed against body weight), post-operative transfusion of blood products including packed red blood cells, fresh frozen plasma and platelets, postoperative hospital stay, and re-exploration for bleeding, tamponade or other cardiac complication rate. Patients with high body mass index (BMI) defined as BMI ≥ 30 kg/m² are subdivided into two groups depending of having post-operative Protamine. Blood loss and blood products transfusion were analysed to study the effect of Protamine infusion in this group of patients.
Results were statistically analysed using the chi-squared test for categorical data and the 2-sample t-test for continuous data. P<0.05 was considered statistically significant.