Anticoagulation of children undergoing cardiopulmonary bypass is overestimated by current monitoring techniques.

HYPOTHESIS Children who undergo cardiopulmonary bypass (CPB) are proportionally more hemodiluted than adults who undergo CPB. Current methods of monitoring high-dose heparin sulfate anticoagulation are dependent on fibrinogen level. Because of the decreased fibrinogen levels in children, current methods of monitoring heparin anticoagulation overestimate their level of anticoagulation. DESIGN Prospective controlled trial. MAIN OUTCOME MEASURE Production of thrombin (adequacy of anticoagulation). METHODS Children and adults undergoing cardiac surgery who received CPB were anticoagulated in the standard fashion as directed by activated clotting time (ACT) results. Each subject had blood sampled at baseline; heparinization; start of the CPB; CPB at 30, 60, and 90 minutes; and at termination of CPB. Samples were used to assess anticoagulation with the Heparin Management Test (less dependent on fibrinogen level than ACT). We also assessed 2 subclinical markers of thrombosis, thrombin-antithrombin complexes and prothrombin fragment F1.2; a marker of procoagulant reserve, fibrinogen; the natural antithrombotic, antithrombin; and heparin concentration. RESULTS Ten children and 10 adults completed the study. Children had lower fibrinogen levels than adults throughout CPB (P<.05). All adults had both therapeutic ACT and Heparin Management Test levels measured throughout CPB. Although children had therapeutic ACT levels, their Heparin Management Test levels were subtherapeutic while undergoing CPB. The children had significantly higher thrombin-antithrombin complexes and prothrombin fragment F1.2 than adults, indicating ongoing thrombin production (P<.01). The increases in thrombin-antithrombin complexes and prothrombin fragment F1.2 in children were inversely proportional to their weight. CONCLUSIONS Children undergoing CPB with heparin dosing adjusted to optimize the ACT manifest inadequate anticoagulation (ongoing thrombin formation). High-dose heparin anticoagulation therapy in children undergoing CPB should be directed by tests (like the Heparin Management Test) that are less dependent on fibrinogen level than ACT.