What value act should be run during cardiopulmonary bypass (CPB)?

From the Guidelines

During cardiopulmonary bypass (CPB), the activated clotting time (ACT) should be maintained above 250 seconds, as this threshold has been shown to be safe and effective in patients undergoing CABG with heparin-coated circuits 1. The traditional target ACT of >480 seconds during CPB has been challenged in numerous clinical studies, suggesting that a lower threshold may be sufficient in certain contexts.

• The use of heparin-coated circuits has been shown to reduce the risk of thromboembolic events and clotting incidents, even at lower ACT levels 1.
• A large cohort study from two centers reported that a target ACT between 250 and 300 seconds was safe and effective in patients undergoing CABG with heparin-coated circuits 1.
• A small randomized controlled trial (RCT) also demonstrated the clinical safety of an ACT below 300 seconds in CABG procedures using MiECC 1. However, it is essential to note that the required safe ACT depends on the specifics of the circuits used, and further research is warranted to fully understand the relationship between ACT and CPB outcomes 1. In contrast, a more recent study proposed a standardized definition of heparin resistance in adult cardiac surgery, suggesting that an ACT target of 480 seconds or more after 500 U/kg of heparin should be used to guide clinical management 1.
• However, this study did not provide new evidence on the optimal ACT target during CPB, and its recommendations are based on a review of existing literature rather than new clinical data. Therefore, based on the most recent and highest-quality evidence, maintaining an ACT above 250 seconds during CPB appears to be a safe and effective strategy in patients undergoing CABG with heparin-coated circuits 1.

From the FDA Drug Label

Patients undergoing total body perfusion for open-heart surgery should receive an initial dose of not less than 150 units of heparin sodium per kilogram of body weight. Frequently, a dose of 300 units per kilogram is used for procedures estimated to last less than 60 minutes, or 400 units per kilogram for those estimated to last longer than 60 minutes.

The value to act on during cardiopulmonary bypass is to maintain an activated clotting time (ACT), although the exact target value is not specified in the label. However, the label does provide guidance on the initial dose of heparin sodium per kilogram of body weight for patients undergoing total body perfusion for open-heart surgery.

• Initial dose: not less than 150 units of heparin sodium per kilogram of body weight
• Dose for procedures less than 60 minutes: 300 units per kilogram
• Dose for procedures more than 60 minutes: 400 units per kilogram 2

From the Research

Activated Clotting Time Monitoring During Cardiopulmonary Bypass

• The activated clotting time (ACT) is a crucial parameter to monitor during cardiopulmonary bypass (CPB) to ensure adequate anticoagulation 3, 4.
• A study published in 2004 found that an ACT of > 350 seconds at 5 min after heparin administration is sufficient to ensure adequate anticoagulation during hypothermic CPB, and subsequent monitoring is not necessary 3.
• However, another study published in 1994 found that ACT measurements do not correlate well with plasma heparin concentration during CPB, and whole blood heparin concentration measurements may be a better indicator of anticoagulation 5.
• The choice of ACT measurement method can also affect the results, with different methods (e.g. celite, kaolin, and MAX-ACT) showing varying degrees of correlation with each other and with plasma heparin concentration 6.

Factors Affecting Activated Clotting Time Measurements

• Temperature: Hypothermia can increase ACT measurements, while normothermia can decrease them 6.
• Aprotinin: The presence of aprotinin can prolong C-ACT measurements, but not MAX-ACT or K-ACT measurements 6.
• Hematocrit: Reduced hematocrit can affect ACT measurements, particularly during CPB 5.

Heparin Dosing and Monitoring

• The initial heparin dose and subsequent monitoring can affect the risk of thrombosis and bleeding during CPB 4, 7.
• A study published in 1990 found that higher heparin doses and concentrations during CPB can increase the risk of postoperative bleeding 7.
• The use of whole blood heparin concentration measurements may be a better indicator of anticoagulation than ACT measurements during CPB 5, 7.