Protamine sulfate is routinely used to reverse heparin anticoagulation after cardiopulmonary bypass (CPB). The conventional dosing strategy of 1 mg protamine per 100 IU of heparin may result in excess protamine exposure, which has been associated with anticoagulant effects, platelet dysfunction, and hemodynamic instability. Recent evidence suggests that lower protamine doses may provide adequate heparin reversal while reducing potential adverse effects. 

This multicenter, prospective, randomized, double-blind, controlled trial aims to compare three protamine-to-heparin dosing ratios (1:1, 0.8:1, and 0.75:1) in adult patients undergoing elective cardiac surgery requiring cardiopulmonary bypass. The primary outcome is activated clotting time (ACT) measured 5 minutes after protamine administration. Secondary outcomes include the need for additional protamine administration, protamine-related adverse events, postoperative bleeding, blood product transfusion requirements, and length of intensive care unit stay. 

The results of this study may help determine whether reduced protamine dosing can safely achieve effective heparin reversal while minimizing drug exposure and potential complications after cardiopulmonary bypass. 

Heparin is routinely administered during cardiopulmonary bypass (CPB) to prevent clot formation in the extracorporeal circuit. At the end of CPB, protamine sulfate is used to neutralize the anticoagulant effect of heparin. The conventional protamine dosing strategy is 1 mg of protamine for every 100 IU of the initial heparin dose administered. However, emerging evidence suggests that this standard dosing regimen may result in excessive protamine exposure, which has been associated with adverse effects such as hypotension, pulmonary hypertension, platelet dysfunction, and paradoxical anticoagulation.

Recent studies have suggested that reduced protamine dosing strategies may achieve adequate reversal of heparin anticoagulation while minimizing potential complications associated with protamine administration. However, the optimal protamine-to-heparin ratio remains uncertain.

This randomized clinical study aims to compare different protamine dosing strategies for heparin reversal after cardiopulmonary bypass in adult patients undergoing cardiac surgery. Participants will be randomized to receive one of three protamine dosing regimens based on the initial heparin dose administered during CPB: the conventional 1:1 ratio (1 mg protamine per 100 IU heparin), a reduced dose ratio of 0.8:1, or a further reduced ratio of 0.75:1.

The study will evaluate the effectiveness of these dosing strategies in achieving adequate heparin reversal as measured by activated clotting time (ACT), as well as clinical outcomes including the need for additional protamine administration, postoperative bleeding, transfusion requirements, protamine-related adverse events, re-exploration for bleeding, and duration of intensive care unit stay.

Inclusion Criteria:

• Age ≥18 years
• Patients scheduled for elective cardiac surgery requiring cardiopulmonary bypass (CABG, valve surgery, or combined procedures)
• Patients receiving systemic heparinization according to the institutional cardiopulmonary bypass protocol
• Ability to provide written informed consent before surgery

Exclusion Criteria:

• Known allergy or hypersensitivity to protamine
• Pre-existing coagulopathy or bleeding disorders
• Patients receiving chronic anticoagulation that cannot be safely discontinued before surgery
• Severe renal dysfunction
• Severe hepatic dysfunction
• Emergency cardiac surgery
• Pregnancy
• Off-pump cardiac surgery

Protamine doses will be prepared by an unblinded perfusionist or pharmacist in indistinguishable syringes according to the randomized allocation. The surgical, anesthesia, and intensive care teams, as well as patients and outcome assessors, will remain blinded to group assignment.