The precise amount of protamine required to neutralize unfractionated heparin (UFH) remains unknown. This study will systematically identify the doze needed to neutralize UFH following cardiopulmonary bypass (CPB).

The precise dose of protamine needed to neutralize unfractionated heparin (UFH) is unknown. Research suggests that low dose protamine is associated with decreased need for transfusions in cardiac surgery. The ATS guidelines recommend that half of the total UFH dose given for cardiopulmonary bypass (CPB) should be neutralized with protamine. However, it is unknown if this is routinely followed by anesthesiologists. Furthermore, the reference standard for UFH has changed recently and it is unknown how this has affected the dose of protamine in the perioperative period. Protamine does have a very short life and heparin rebound occurs very commonly.

It is common practice to divert the suctioned mediastinal blood following CPB while the patient is still anticoagulated. The traditional practice is that once half dose protamine has been given, suction to the cardiotomy reservoir is turned off. All surgical field blood loss is then diverted to wall suction. The inherent risk of letting too much protamine into the CPB reservoir is that UFH therein may get neutralized and predispose to clot formation in the venous reservoir. This precludes an emergency 'crash' on to CPB, should that be required for some reason. Experience of the Investigators indicates that most surgeons will turn off suction leading to the cardiotomy reservoir once half the total protamine dose has been administered. The concern with this is that "half dose" protamine may be quite different for different anesthesiologists.

The research investigators hypothesize low dose protamine is sufficient to neutralize the effects of UFH as monitored through activated clotting time (ACT). Anesthesiologists administer varying doses of protamine to neutralize UFH in cardiac surgery and the rationale behind such decisions is unclear.

Thus, the primary objective of this study is to evaluate the dose of protamine required to neutralize UFH following CPB. Secondary objectives are 1) to assess the amount of protamine needed to neutralize UFH in intravenously administered cardiotomy reservoir blood. 2) To examine the amount of residual heparin postoperatively in the cardiac surgery ICU; 3) to examine, through semi-structured interviews, the decision-making processes involved in managing (anti)coagulation in cardiac surgery.

Inclusion Criteria:

• Elective cardiac surgery patients > 18 years age who can provide written consent for the study.

Exclusion Criteria:

• History of any known coagulopathies, liver dysfunction, previous cardiac surgery, preoperative abnormal coagulation profiles, recent exposure to heparin (unfractionated or low molecular weight), warfarin, clopidogrel or other direct thrombin inhibitors in the preceding 7 days.
• History of heparin resistance
• History of adverse reactions to protamine
• Patients identified as having heparin resistance
• Anticipated CPB time > 2-2.5 hrs