Upon joining the study, the patient is confirmed to meet the inclusion criteria, which include being scheduled for cardiac surgery with cardiopulmonary bypass (CPB) and having heparin resistance.

The patient must be between 18 and 85 years old and provide informed consent. Female patients of childbearing potential must have a negative pregnancy test within 14 days prior to surgery.

Before surgery, the patient receives an intravenous administration of 500 units per kilogram of body weight of unfractionated heparin (UFH).

The patient’s activated clotting time (ACT) is measured between 2 and 5 minutes after heparin administration to confirm heparin resistance, defined as an ACT less than 480 seconds.

The patient is randomly assigned to receive either Atenativ or a placebo. Atenativ is a human plasma-derived antithrombin administered intravenously.

The study evaluates two different doses of Atenativ to determine its effectiveness in restoring and maintaining heparin responsiveness during surgery.

The patient undergoes cardiac surgery with CPB. The effectiveness of Atenativ or placebo in maintaining heparin responsiveness is monitored.

Additional therapies containing antithrombin may be administered if necessary to maintain heparin responsiveness.

After surgery, the patient is monitored for 24 hours to assess heparin responsiveness and any need for further antithrombin therapy.

The patient’s recovery, including chest tube drainage and any need for reoperation due to bleeding, is evaluated.

The patient’s survival status and any adverse events are recorded and compared across the different treatment groups.

The length of stay in the intensive care unit (ICU) and other recovery parameters are assessed to evaluate the overall effectiveness and safety of Atenativ.