Heparin is used during open abdominal aortic aneurysm (AAA) surgery to reduce thrombo-embolic complications (TEC): such as myocardial infarction, stroke, peripheral embolic events and the related mortality. On the other hand, heparin may increase blood loss, causing harm for the patient.~Heparin has an unpredictable effect in the individual patient. The effect of heparin can be measured by using the Activated Clotting Time (ACT). ACT measurement in open AAA repair could be introduced to ensure the individual patient of safe, tailor-made anticoagulation with a goal ACT of 200-220 seconds. A randomized controlled trial (RCT) has to prove that ACT guided heparinization would result in fewer TEC and lower mortality than a standardized bolus of heparin of 5 000 international units (IU), the current gold standard. ACT guided heparinization results in higher doses of heparin during operation and this should not result in significantly more bleeding complications of importance.~The ACTION-1 study will evaluate the effect of weight dosed heparinization during open abdominal aortic aneurysm surgery.The study will be an international multi-centre single blind randomized controlled trial. Patients will be randomized using a computerized program (CASTOR EDC) with a random block size of a maximum of 8. The randomization will be stratified by participating centre. Separate evaluation of results and if complications can be labelled as TEC, will be performed by an Independent Central Adjudication Committee. The 3 members of this Committee will be blinded with regard to if the patient was randomized for ACT guided heparinization or standard bolus of 5 000 IU without ACT measurements.~In the intervention group, heparin is given to reach an ACT of 200-220 seconds. Based on the ACT, an additional dose of heparin will be administered. Five minutes after every administration of heparin the ACT is measured. If the ACT is 200 seconds or longer, the next ACT measurement is performed every 30 minutes, until the end of the procedure or until new heparin administration is required (because of ACT < 200 seconds). Depending on the ACT value near the end of surgery, protamine will be given to neutralize the effect of heparin.~In the comparative group, a single dose of 5 000 IU of heparin will be given 3-5 minutes before clamping of the aorta. No ACT measurements will be performed, except for one ACT measurement after re-establishing blood flow and removing all clamps. Depending on that ACT value near the end of surgery, the local protamine can be given to neutralize the effect of heparin.
Aim of the ACTION-1 study is to determine whether ACT guided heparinization decreases thrombo-embolic complications (TEC) and mortality after elective open AAA surgery, without causing more bleeding complications.