Appropriate dose of postoperative intravenous heparin infusion in the children undergoing modified blalock taussig shunt 4 mm and below in size

Background: Modified Blalock-Taussig shunt is the most common palliative systemic to pulmonary artery shunt performed in cyanotic congenital heart disease. Shunt thrombosis occurred in 1 to 17% of the operation that led to mortality. One major risk factor is a small shunt size under 4 mm. Systemic heparinization is a preventive measure for this subgroup with a cost of a bleeding complication. However, there is no standard dose for heparin infusion. The objective of this study is to determine the appropriate dose of heparin infusion to achieve APTT ratio of 1.5 to 2. Materials and Methods: During 2007 to 2016, 220 patients who underwent off-pump modified Blalock-Taussig shunt of 4 mm and below in size at Siriraj Hospital were studied. After exclusion of the patients with pre-operative coagulopathy (APTT >30.5 sec), out of target APTT ratio and missing data, 60 patients were included. Demographic data, operative parameter, heparin infusion dosage, postoperative complications such as shunt thrombosis and postoperative bleeding were analyzed. Results: Appropriate heparin infusion dose to achieve an APTT ratio of 1.5 to 2.0 was 18.27+8.84 unit/kg/hour. In the patient weight less than 2.5 kg, heparin infusion dose was 14.25+4.92 unit/kg/hour and never exceed 20 unit/kg/hour. Shunt thrombosis and bleeding complication were occurred in 11.7% and 8.3% of patients, respectively, without correlation to heparin dosage and time to achieve therapeutic APTT ratio. Conclusion: To achieve an APTT ratio of 1.5 to 2, postoperative intravenous heparin infusion should be 18 unit/kg/hour. A smaller dose should be considered in low birth weight patients.