Failure to achieve therapeutic anticoagulation in the first 24 hr after pulmonary embolism (PE) is associated with increased rate of recurrence in subsequent months. A weight-based nomogram is recommended for unfractionated heparin (UFH) to achieve the target PTT. However, for obese patients, the nomograms may not be accurate and would necessitate very high doses if followed. Clinicians hesitate to use UFH nomograms in obese patients for fear of bleeding complications.
We retrospectively reviewed the records of all obese patients (BMI > 29) diagnosed with PE at our institution over a six month interval who were treated with UFH. Patient data obtained included weight, age, height, and method of diagnosis of PE. We recorded the initial bolus and infusion rate of UFH as well as the infusion rate that ultimately achieved a therapeutic PTT (60-90 sec).
Eight patients met all inclusion criteria. Their mean age was 58 yr (range 25-80 y). Six were females. BMI (mean) was 36 kg/m2 (range 29.3 - 44). Despite hospital guidelines, actual body weight (ABW) based nomogram was not used for either the bolus or the infusion rate. The average bolus was 55 units/kg (range 34-76). The average initial infusion rate was 14 units/kg (range 11-16). With these initial doses, 50% were over-anticoagulated and 25% were under-anticoagulated. The average infusion rate to maintain therapeutic PTT was 12.8 units/kg (range 8.4-15.8).
Weight based nomograms overestimate the dose of UFH required to achieve therapeutic aPTT. By contrast, calculations based on ideal body weight (IBW) result in inadequate anticoagulation. In the majority of patients the dose that produced a therapeutic PTT was 40% of the difference between the dose calculated based on IBW and ABW.
The optimal dose of UFH to achieve a therapeutic PTT in obese patients should not be based on either ABW or IBW but rather an estimated value around 40% above the IBW. However, our data are based on a small population and should be confirmed with a larger sample.
Samar Khan, None.