Effect of Body Mass Index on Bleeding Frequency and Activated Partial Thromboplastin Time in Weight-Based Dosing of Unfractionated Heparin: A Retrospective Cohort Study

OBJECTIVE: To assess bleeding and activated partial thromboplastin time (APTT) In relation to body mass Index (BMI) In patients prescribed weight-based dosing of intravenous unfractionated heparin (UFH) for cardiac Indications without a maximum (dose-capped) initial bolus or capped initial Infusion rate. PATIENTS AND METHODS: Consecutive patients admitted to an academic medical center from February 1, 2002, through November 31, 2003, who were treated with a UFH nomogram consisting of a 60-U/kg Intravenous bolus plus an Initial continuous Intravenous Infusion of 12 U/kg hourly and titrated to a goal APTT range corresponding to thromboplastin-adjusted target heparin levels of 0.3 to 0.7 U/mL by anti-Xa assay were evaluated for this retrospective cohort study. Patients were excluded If they concomitantly received a fibrinolytic, glycoprotein IIb/IIIa Inhibitor, or any other antithrombotic agent (except warfarin). Study patients were divided Into quartiles by BMI. RESULTS: Of the 1054 patients Included In the study, 807 (76.6%) had an Initial bolus dose higher than 4000 U, and 477 (45.3%) had an Initial Infusion rate higher than 1000 U/h. Despite a significant difference among BMI quartiles In proportion of supratherapeutic first APTT values (P<.001), no statistically significant difference was found In bleeding frequency (P=.26) or frequency of first APTT within the goal range (P=.27). Logistic regression analyses revealed that BMI was not a significant predictor of bleeding or first APTT within the goal range. CONCLUSION: We did not find any difference in the proportion of first APTT values In the goal range or an Increased risk of bleeding In obese patients treated with UFH without a capped Initial dose. Our data demonstrate the safe use of weight-based UFH without a capped Initial bolus dose or capped Initial Infusion rate In patients with medical cardiac conditions.