Low molecular weight heparin for venous thromboembolism prophylaxis in general Intensive Care Unit patients: an anti-factor Xa level-based approach

BACKGROUND: Venous thromboembolism (VTE) in the Intensive Care Unit (ICU) is associated with significant mor-bidity and mortality therefore prevention is imperative to reduce its burden. VTE prophylaxis in ICU patients is primarily pharmacological using low molecular weight heparin (LMWH). Plasma anti-factor Xa (anti-FXa) levels may be used to measure LMWH activity. This study aims to determine the proportion of acutely ill patients in a general ICU receiving standard VTE prophylaxis that achieve adequate peak or trough anti-FXa prophylactic levels and to determine the effect of LMWH dose adjustment in patients not achieving adequate anti-FXa prophylactic levels.METHODS: Peak and trough anti-FXa levels were measured at four and 23 hours respectively after receiving the second consecutive daily enoxaparin 40 mg sc injection. Patients in whom peak anti-FXa levels were found to be sub -prophy-lactic (<0.2 IU/mL), were dose escalated to enoxaparin 60 mg once daily. Peak and trough levels were repeated as above.RESULTS: Sixty-one percent of study patients (N.=46) were found to have sub-prophylactic peak anti-FXa levels. Twenty-seven patients received an increased enoxaparin dose of 60 mg/d. Of these, nine patients (33.3%) still failed to achieve the target prophylactic peak anti-FXa level (0.2-0.4 IU/mL). Male gender and high body mass index (BMI) were significantly and strongly correlated with sub-prophylactic anti-FXa levels.CONCLUSIONS: Most ICU patients in this study did not achieve recommended prophylactic anti-FXa levels while re-ceiving a standard dose of enoxaparin and these levels failed to increase after enoxaparin dose escalation in a significant proportion of patients. High BMI and male gender are associated with sub-prophylactic levels of anti-FXa in critically ill patients.