Standard subcutaneous dosing of unfractionated heparin for venous thromboembolism prophylaxis in surgical ICU patients leads to subtherapeutic factor Xa inhibition

Purpose: To assess coagulation status and factor Xa inhibition in surgical intensive care unit (ICU) patients administered prophylactic unfractionated heparin for venous thromboembolism (VTE) prophylaxis. Methods: We conducted a randomized, single-blind study at a tertiary academic medical center. Included were patients 18 years and older admitted to the surgical ICU directly after major abdominal surgery. Exclusion criteria included significant bleeding risk, preoperative anticoagulation, or history of heparin-induced thrombocytopenia. Patients were randomized to two regimens for VTE prophylaxis: standard of care unfractionated heparin, 5,000 units subcutaneously three times daily (SQH) versus unfractionated heparin via intravenous infusion, titrated to an activated partial thromboplastin time of 40-45 s (IVH). Blood samples were taken prior to surgical incision on day 0 and daily for 5 days after surgery. Samples were analyzed for factor Xa inhibition and viscoelastic whole blood clotting parameters (Sonoclot analyzer). Results: A total of 50 patients were randomized to either SQH or IVH. The majority of patients had cancer. Patients in the SQH group had no detectable peak anti-factor Xa (aFXa) activity for 5 days after surgery, while patients in the IVH group had statistically elevated levels compared to the SQH group on days 3-5. SQH patients demonstrated a hypercoagulable profile on Sonoclot, while IVH patients displayed a normal profile. Conclusions: Standard of care subcutaneous dosing of unfractionated heparin for VTE prophylaxis in surgical ICU patients leads to subtherapeutic levels of factor Xa inhibition.