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

Hypothesis: Children who undergo cardiopulmonary bypass (CPB) are proportio nally more hemodiluted than adults who undergo CPB. Current methods of moni toring high-dose heparin sulfate anticoagulation are dependent on fibrinoge n level. Because of the decreased fibrinogen levels in children, current me thods of monitoring heparin anticoagulation overestimate their level of ant icoagulation. Design: Prospective controlled trial. Main Outcome Measure: Production of thrombin (adequacy of anticoagulation). Methods: Children and adults undergoing cardiac surgery who received CPB we re anticoagulated in the standard fashion as directed by activated clotting time (ACT) results. Each subject had blood sampled at baseline; hepariniza tion; start of the CPB; CPB at 30, 60, and 90 minutes; and at termination o f CPB. Samples were used to assess anticoagulation with the Heparin Managem ent Test (less dependent on fibrinogen level than ACT). We also assessed 2 subclinical markers of thrombosis, thrombin-antithrombin complexes and prot hrombin fragment F1.2; a marker of procoagulant reserve, fibrinogen; the na tural 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 Tes t levels were subtherapeutic while undergoing CPB. The children had signifi cantly higher thrombin-antithrombin complexes and prothrombin fragment F1.2 than adults, indicating ongoing thrombin production (P<.01). The increases in thrombin-antithrombin complexes and pro thrombin fragment F1.2 in child ren were inversely proportional to their weight. Conclusions: Children undergoing CPB with heparin dosing adjusted to optimi ze the ACT manifest inadequate anticoagulation (ongoing thrombin formation) . High-dose heparin anticoagulation therapy in children undergoing CPB shou ld be directed by tests (like the Heparin Management Test) that are less de pendent on fibrinogen level than ACT.