Venous thromboembolism (VTE), comprising deep venous thrombosis (DVT) and venous pulmonary embolism (PE), is a common and preventable complication in patients undergoing rehabilitation, which can result in significant morbidity and death [1–7]. Prolonged bed rest (> 14 days) is associated with a five-fold increased risk of developing DVT [4]. The American Society of Haematology (ASH) 2018 guidelines for the management of VTE states that the risk of VTE persists for 45–60 days following discharge from acute hospitalisation [8]. The rate of DVT has been reported as high as 33% among people undergoing rehabilitation for a variety of conditions [2]. The current study focused on two common clinical rehabilitation in-patient scenarios: patients recovering from acute ischemic stroke (AIS) or recovering from acute spinal cord injury (SCI). There is a large body of evidence that describes the prevalence of VTE in these areas [1, 3, 9–12]. Depending on the diagnostic methods and time of evaluation, the incidence of DVT without prophylaxis is 20–50% following stroke and 60–80% following SCI [1, 13]. Risk factors for developing DVT in these patients include immobility, older age (> 65 years), female gender, obesity (body mass index (BMI) ≥25kg/m2), active cancer and muscle weakness [1, 3, 9].
The symptoms of DVT and pulmonary embolism (PE) are often non-specific, especially in patients undergoing rehabilitation who may under-report symptoms due to aphasia, cognitive impairment or altered conscious states [2]. VTE often presents as simply fever and leg edema [14]. Due to the difficulty associated with diagnosis, administration of routine prophylactic therapy is recommended by multiple guidelines for patients hospitalized for rehabilitation for a variety of diagnoses [8, 10, 15]. VTE prevention therapy for survivors of ischemic stroke is recommended for the duration of in-patient rehabilitation or until the stroke survivor regains mobility [3]. Based on the severity of the SCI, low molecular weight heparin (LMWH) are recommended for up to 24 weeks after injury [13].
Enoxaparin, a LMWH, is considered the standard prophylactic treatment for patients undergoing rehabilitation for AIS or SCI [3, 8, 10]. Enoxaparin is a convenient option for thromboprophylaxis due to its predictability in regards to dose response, long half-life and lower risk of bleeding for a given antithrombotic effect [16]. Several doses and treatment regimens have been proposed; however, a fixed dose of 40mg once daily is the accepted, prevailing approach and is considered the standard prophylactic dose [12, 17, 18]. In clinical practice, a fixed dose regimen is frequently used, with the exception of patients who are underweight, obese, pregnant, or suffering from renal insufficiency (creatinine clearance (CrCl) < 30 ml/min) [19, 20].
The anti-factor Xa (anti-Xa) assay is a functional assay that helps measure antithrombin (AT)-catalyzed inhibition of factor Xa by Unfractionated Heparin (UFH) and direct inhibition of factor Xa (FXa) by enoxaparin. As a result, the anti-Xa level reflects the in-vivo pharmacological activity of enoxaparin. For prevention of DVT/PE, steady state peak Anti-Xa activity measured three hours post-drug administration following three consecutive days of enoxaparin treatment or more is considered to be 0.2–0.5 IU/ml [21, 22].
Several studies examining anti-Xa activity with the fixed enoxaparin prophylactic dosing have reported shortcomings for several clinical scenarios. For example, critically ill, trauma and burn, plastic surgery, renal and oncology patients often demonstrate low plasma anti-factor Xa (anti-Xa) levels, suggesting inadequate prophylaxis (sub/supra prophylaxis) and which may lead to an increased risk of thrombotic and bleeding events [17–19, 21, 23–28]. To the best of our knowledge, similar investigations have not been reported in the literature for patients in a rehabilitation setting.
The current study was devised to examine the efficiency of fixed dose enoxaparin as a thromboprophylaxis strategy for patients recovering from SAIS or SCI admitted to a rehabilitation hospital. The goal of this study was to evaluate in-vivo enoxaparin activity in these patients, and to evaluate the influence of co-variables (e.g., renal function, weight) on the outcome of this treatment strategy.