Effectiveness of estimated blood volume-guided prophylactic enoxaparin dosing in patients following minimally invasive surgery.

BACKGROUND

Enoxaparin is commonly used for venous thromboembolism prophylaxis in surgical patients. Whether body mass index or estimated blood volume-based dosing better achieves target anti-factor Xa levels remains unclear. We compared body mass index and estimated blood volume-based dosing for accuracy in achieving target anti-factor Xa levels.

METHODS

Patients underwent primary or revisional minimally invasive surgery from January 2015 to June 2024. Inclusion required an anti-factor Xa drawn 2.5-6 hours after 3 consecutive enoxaparin doses. The target range for anti-factor Xa draw was 0.2-0.5 IU/mL. Enoxaparin was dosed based on estimated blood volume using the following guidelines: estimated blood volume 3-4.9 received 30 mg twice daily, estimated blood volume 5-6.9 received 40 mg twice daily, and estimated blood volume >7 received 60 mg twice daily. The dosage based on body mass index used the following: body mass index 18-40 received 40 mg once daily, body mass index 40-50 received 40 mg twice daily, and body mass index >50 received 60 mg twice daily.

RESULTS

Two hundred eighty-seven patients were included for analysis (137 received body mass index dosing, 150 received estimated blood volume dosing). The mean anti-factor Xa level for the estimated blood volume-dosed cohort was 0.27 compared with 0.36 for the body mass index cohort. Estimated blood volume-based enoxaparin dosing produced less variability of anti-factor Xa values than body mass index-based dosing. Spearman rank correlation coefficient showed that estimated blood volume tracks more closely to anti-factor Xa than body mass index.

CONCLUSION

Estimated blood volume-based enoxaparin dosing resulted in lower and more consistent anti-factor Xa levels compared with body mass index-based dosing and demonstrated a stronger correlation with anticoagulant exposure. However, subtherapeutic levels were more frequent with estimated blood volume-based dosing, highlighting ongoing challenges in achieving optimal prophylaxis with current dosing strategies.