In pediatric cardiac surgery, anticoagulation protocols are derived from adult protocols. Age, Antithrombin III level, and capacity to generate thrombin are factors that affect unfractionated heparin (UFH) action in children. A starting UFH dose of 400 UI/kg is recommended to get an Activated Clotting Time (ACT) target over 400seconds. In our daily practice, we noticed a wide range of ACT increase (ΔACT) after this standardized weight based bolus of UFH.

To define factors affecting UFH effectiveness based on ΔACT before CPB initialization in pediatric cardiac surgery.

A retrospective chart review of patient undergoing cardiac surgery requiring CPB in a single university hospital was performed. Patients receiving preoperative anticoagulation therapy or platelet aggregation inhibitors were excluded. We searched predictive factors for ΔACT. We defined 2 groups: hyperrespondents (HR; ΔACT>500) and normorespondents (NR; ΔACT<500).

Seventy-nine charts were reviewed. Median [25–75] age and weight were respectively 13.8 [5–72] months and 8.7 kg [5.5–18.8]. UFH pre CPB bolus was 384 [358–410] to increase pre operative ACT from 124 [115–137] to 536 s[463–582]. HR are younger (4.9 [3.7–13] vs 24.6 [5.7–76] months, P<0.05) and have smaller weight (6,1 [4.6–7.8] vs 10 kg[5,8–19.5], P<0,05) than NR. ΔACT is correlated to UFH dose for patients>5 months (r=0.59 P=0.00001) and>5kg (r=0.54 P=0.00001) for with a predictive ΔACT of 386 s [325–443]. There is no correlation between ΔACT and UFH dose for patients<5 months and<5kg.

A dose UFH of 400 UI/kg before starting CPB in pediatrics is overestimated, especially for children<5 months and<5kg. Accurate dose for ACT target>400 s in this specific population should be calculated using other method that still needs to be developed to avoid complications associated to excessive dose of UFH.