Retrospective Evaluation of Dosing Body Weight for Unfractionated Heparin in Obese Patients

Purpose: Using adjusted body weight (AdjBW) for heparin dosing in obese patients is a common but not validated clinical practice. The purpose of this study was to evaluate whether using AdjBW in obese patients would lead to quick achievement of therapeutic activated partial thromboplastin time (aPTT) and low bleeding risk with heparin therapy. Methods: A retrospective cohort study was conducted in patients that received heparin before and after implementation of a revised heparin protocol that utilized AdjBW for obese patients. The primary outcome was percentage of first aPTT values within the therapeutic range. Secondary outcomes included time to first therapeutic aPTT and clinically significant bleeding. Results: There was no difference in the primary outcome in obese compared to non-obese patients in the pre-implementation group (11% vs. 15%) or post implementation group (17% vs. 21%). No difference was seen in time to first therapeutic aPTT between obese and non-obese patients in either group. However, obese patients in the post-implementation group achieved therapeutic aPTT significantly faster than obese patients in pre-implementation group (14 vs. 24 hours, p = 0.002). Clinically significant bleeding was higher in obese than non-obese patients prior to implementation (11% vs. 1%, p = 0.01), but no difference was seen after implementation. Conclusion: Although there was no difference in the first aPTT values, more bleeding was seen in obese patients when actual body weight was used for heparin dose calculation. When AdjBW was used for dosing in obese patients, it was associated with faster achievement of therapeutic aPTT.