Clinical reports suggest UFH-related major bleeding rates of up to 24% in children. Current recommendations for UFH therapy recommend a 75-100IU/kg bolus followed by an age-dependent continuous infusion rate. This recommendation is based on a study that first measured UFH response 6hrs post commencement; at that time, 39% of patients achieved a minimum level APTT (>55sec). We evaluated laboratory response to a single UFH bolus dose of 75-100u/kg in children <16years of age (n=64) to determine the independent impact of UFH bolus on anticoagulation levels in children. Venous blood was collected from a dedicated IV at 15, 30, 45 and 120mins post UFH dose. APTT and anti-Xa assays were performed. The upper limit of the APTT assay was modified to measure time to clot formation up to 999secs. APTT and anti-Xa results for samples collected at 15 and 120mins post bolus are presented in the table.
67% of all APTT assays performed at 15, 30 and 45mins post bolus were >999secs. Current bolus recommendations give very high anticoagulant effect out to 120mins post bolus dose, without concurrent continuous infusion. Despite very high APTT and anti-Xa levels, there were no major bleeding events. Lack of target APTT range achievement in previous paediatric studies may reflect the need for modified continuous