The ATLANTIC study: Anti-Xa level assessment in trauma intensive care.

OBJECTIVE: To quantify the pharmacodynamic (PD) activity of daily subcutaneous (SC) enoxaparin as venous thromboembolism (VTE) prophylaxis in high-risk trauma patients admitted to the intensive care unit (ICU). METHODS: This was a prospective observational PD study conducted in the ICU of a state-wide major trauma referral centre. The study cohort included adult patients admitted to the ICU with a high risk of VTE, as defined by at least one of the following: age > 40 years, prior VTE, spinal cord injury (SCI), traumatic brain injury (TBI), major venous injury, pelvic fractures, spinal fractures requiring treatment, severe lower limb injuries, and major surgery >2 h in duration. Standard prophylactic enoxaparin dosing was 40 mg SC daily, unless amended by the treating clinician. Plasma anti-Xa activity was measured approximately 60 min before dosing (trough activity), and at 3-5 h after dosing (peak activity). Target peak and trough activity were defined as >0.2 IU/mL and >0.1 IU/mL respectively. Clinical data including the development of VTE and haemorrhagic complications were collected. RESULTS: Twenty-five patients were enrolled. Median [IQR] age, weight, and plasma creatinine were 59 years [36,70], 85 kg [76.5,93.5] and 70µmol/L [60.5,109] respectively. Median APACHE III and Injury Severity Score were 54 [42.5,66.5] and 27 [17,34] respectively. Thirteen patients suffered a TBI, in 12 cases surgery extended beyond two hours, and five patients had spinal fractures requiring treatment. Twenty-two patients received enoxaparin 40 mg SC daily, two 60 mg, and one 20 mg. Median peak and trough anti-Xa activity was 0.21 IU/mL [0.125,0.25] and 0.01 IU/mL [0,0.05] respectively. Twelve (12/25; 48%) patients had low peak activity ≤0.2 IU/mL. Twenty-one (21/23; 91%) patients had low trough activity (≤0.1 IU/mL) and in six (6/23; 26%) cases, these were undetectable. Eight (8/25; 32%) patients had documented VTE of whom seven had low trough activity. There were no major haemorrhagic complications. CONCLUSIONS: In a cohort of high risk critically ill trauma patients receiving daily SC enoxaparin as VTE chemoprophylaxis, measured peak and trough plasma anti-Xa activity was inadequate in a significant proportion. On this basis, further systematic investigation concerning dose optimisation in this patient population appears warranted.