(971) Evaluating aPTT Prolongation With Heparin Thromboprophylaxis in Underweight Critically Ill Patients

Introduction: Critically ill patients are at an increased risk of developing venous thromboembolism (VTE). Patients with low body weight pose challenges to dosing strategies as they are underrepresented in clinical trials. This study aims to assess the safety and efficacy of VTE pharmacological prophylaxis with subcutaneous heparin (SQH) in critically ill patients with low body weight.

Methods: This single-center retrospective evaluation included low body weight adult patients (weight ≤50 kg or body mass index (BMI) ≤18.5 kg/m2) who received SQH between April 2020 and August 2022. Patients admitted to the intensive care unit (ICU) for at least 48 hours with an active order for SQH ≤15,000 units/day were included. Patients were excluded if SQH was administered for < 48 h, if ≥25% doses were held or if aPTT values were not monitored after SQH initiation. The primary endpoint was the incidence of activated partial thromboplastin time (aPTT) prolongation (≥38.5 seconds). Secondary endpoints included the rates of VTE and major bleeding. Descriptive statistics were used to characterize the data, including number (%), median (IQR), and Student’s t test or Wilcoxon rank sum test.

Results: A total of 53 patients were included, with a baseline median weight of 44.4 kg and BMI of 17.3 kg/m2. Patients were prescribed SQH 5000 units q8h (n=25), 5000 units q12h (n=27), or 2500 units q8h (n=1). The median aPTT before the first dose of SQH was 32.4 seconds [IQR, 28.6-35.1 seconds]. Prolongation of the aPTT was seen in 60% of patients, with a median increase of 29% over baseline. A significant difference in the frequency of aPTT prolongation was not observed between doses ≤10,000 units/day vs >10,000 units/day (57.1% vs 64%, p=0.610). One patient developed a VTE, and there were similar rates of major bleeding in patients receiving 5,000-10,000 units/day vs >10,000 units/day (17.9% vs 16%, p=1.000). There were no differences in ICU or hospital length of stay, or in-hospital mortality.

Conclusions: aPTT prolongation occurred in 60% of low body weight patients, regardless of dosing strategy. There were no differences in rates of VTE or major bleeding.