Unfractionated Heparin Dosing for Venous Thromboembolism in Morbidly Obese Patients: Case Report and Review of the Literature

Abstract

Unfractionated heparin infusion therapy is often administered using a weight-based dosing strategy for the treatment of venous thromboembolism. In the last several decades, the prevalence of obesity in the United States has increased significantly. The applicability of weight-based heparin dosing recommendations in the obese and morbidly obese population is uncertain, as limited data are available. We describe a 388-kg man who was started on an intravenous infusion of heparin according to hospital protocol for suspected pulmonary embolism. The patient was given a 5000-unit heparin bolus followed by an initial heparin infusion rate of 1500 units/hour, the maximum initial rate specified in the protocol. After additional infusion rate adjustments, a therapeutic activated partial thromboplastin time (aPTT) was reached 55 hours later with a heparin infusion rate of 3650 units/hour. Due to concerns of heparin-induced thrombocytopenia, heparin therapy was discontinued, and fondaparinux 5 mg/day was started. However, heparin therapy was restarted 4 days later for persistent, refractory hypoxemia and recurrent concerns of possible pulmonary embolism. During this second course, a therapeutic aPTT was achieved with a heparin infusion rate of 3550 units/hour. The patient developed bloody pulmonary secretions (with a therapeutic aPTT), necessitating the discontinuation of the heparin infusion. The patient later died after developing pulseless electrical activity. Standard weight-based heparin dosing protocols that specify maximum doses for initial bolus and infusion rates can result in significant delays in time to achieve therapeutic anticoagulation in the obese and morbidly obese patient. Despite limited data on heparin dosing in obesity, we recommend the use of a dosing weight to determine initial heparin dosing when treating venous thromboembolism in morbidly obese patients. It is reasonable to consider one of the following formulas: dosing weight = ideal body weight (IBW) + 0.3(actual body weight [ABW] - IBW), or dosing weight = IBW + 0.4(ABW - IBW).

Treatment of Suspected Pulmonary Embolism in a Super-Obese Individual

“…Therapeutic PTT was maintained with a heparin dosage of 3500-4000 units/h (8.4-9.6 units/kg per hour). This compares well with the case presented by Myzienski and others 3 (BMI 134 kg/m 2 ), in which therapeutic activated PTT was maintained with a dosage of 9.1-9.6 units/kg per hour (based on absolute body weight). In the current case, heparin therapy was discontinued 3 days after initiation because of an interstitial IV line.…”

“…The surgical literature furthers defines BMI of 50 kg/m 2 or above as "super-obesity". 3,6,7 The patient in this case met the definition of super-obesity (see details below).…”

“…[1][2][3] In addition, clinical trials for the treatment of deep vein thrombosis or pulmonary embolism in obese individuals are scarce, with most trials limiting entry to persons weighing no more than 120 kg. 4 The case reported here involved use of unfractionated heparin (UFH) followed by warfarin in a super-obese individual presenting with presumed pulmonary embolism.…”

“…2,3 Using information presented by Myzienski and others 3 in their review of UFH in morbidly obese patients, it was decided to start UFH at 2000 units/h (4.8 units/kg per hour based on absolute body weight) with no bolus dose. Baseline partial thromboplastin time (PTT), measured just before initiation of UFH, was 27.7 s (hospital reference range 22.4-34.5 s).…”

Perioperative management of the obese surgical patient

“…137 However, chemoprophylactic dosing will need to consider that adipose tissue has a lower blood volume than lean tissue; hence, the volume of distribution of heparin will differ in obese patients. Even though heparin dosing requirements do not increase linearly with body weight, 138,139 the 2012 American College of Chest…”