Introduction: Venous thromboembolism (VTE) in the intensive care unit (ICU) is associated with significant morbidity and mortality therefore prevention is imperative to reduce its burden. VTE prophylaxis in ICU patients is primarily pharmacological using low molecular weight heparin. This study aims to determine the proportion of ICU patients receiving VTE prophylaxis that achieves appropriate anti-factor Xa activity (aFXa) prophylactic levels and to characterize this patient population Methods: Seventy-five patients admitted to the General ICU were included. Peak and trough aFXa levels were measured at 4 and 23 hours respectively after receiving the second consecutive daily enoxaparin 40 mg sc injection. Patients in whom peak aFXa levels were found to be sub-prophylactic, peak and trough levels were repeated as above

Inclusion Criteria: Inclusion criteria were age over 18 years and a predicted ICU stay of more than 72 h.

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Exclusion Criteria: Exclusion criteria were any contraindication for heparin-based thromboembolic prophylaxis, patients with an indication for therapeutic anticoagulation , administration of unfractioned-heparin or low-molecular-weight-heparin prior to study entry, active hemorrhage, or creatinine clearance < 30 mL/min.

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