To evaluate the efficacy and safety of weight-based unfractionated heparin (UFH) anticoagulation in obese patients.
Retrospective review of electronic medical records for 88 randomly selected obese patients receiveing UFH infusions from June to December 2004 was conducted to report: 1) adherence to existing anticoagulation guidelines; 2) dose-response relationships according to indication for anticoagulation; and 3) anticoagulant complications.
The indications for anticoagulation were venous thromboembolic disease (VTE) in 38 (43%) and acute coronary syndrome (ACS) in 50 (57%) patients. Mean patient age was 55.6 years and mean weight was 124.7 kg. The recommended guidelines for dosing were followed in 11 % (10/88) of patients. Sixty-nine percent (61/88) of patients received an initial bolus (mean dose 53 units/kg). Mean bolus and infusion rates were 48 units/kg/hour and 13 units/kg/hour respectively for VTE and 57 units/kg/hour and 12 units/kg/hour respectively for ACS. Within 24 hours, 17 (19.3%) patients remained sub-therapeutic, 29 (32.9%) therapeutic (aPTT 46-81 seconds) and 42 (47.8%) in supra-therapeutic aPTT range. Forty-five percent of supra-therapeutic patients received higher heparin doses than recommended by the recent guidelines. Weight-adjusted bolus and infusion rates administered to therapeutic and supra-therapeutic patients were comparable (p=0.15.). Sub-therapeutic patients received a lower infusion rate compared to supratherapeutic patients (p=0.03). There were 5 (5.7%) complications: three bleeding episodes (lower gastrointestinal bleed, retroperitoneal hematoma, epistaxis), and two patients developed heparin induced thrombocytopenia. Both major bleeding complications occurred in patients receiving higher than recommended doses (bolus of 7000 and 8000 units for ACS) resulting in supra-therapeutic aPTT.
Adherence to established anticoagulation guidelines was poor in obese patients. Despite downward adjustments in bolus doses, supra-therapeutic aPTT still occurred in 47.8% of patients thereby increasing the risk of bleeding complications. This study demonstrated variability in dose-response to heparin in the obese that resulted in excessive anticoagulation in some instances.
Reevaluation of the dosing guidelines for UFH in obese patients is warranted.
Jennifer Bonner, None.