Efficacy of standard dose unfractionated heparin for venous thromboembolism prophylaxis in morbidly obese and non-morbidly obese critically Ill patients.

To determine the efficacy of standard dose unfractionated heparin (UFH) for venous thromboembolism (VTE) prophylaxis in critically ill morbidly obese patients. Retrospective single-center observational cohort study in a single tertiary teaching hospital intensive care units (ICUs) in Multiparameter Intelligent Monitoring in Intensive Care II Clinical Database. Patients 18 years or older, admitted to the ICU, and received either UFH 5000 units subcutaneously twice daily or UFH 5000 units three times daily for VTE prophylaxis between 2001 and 2008 were included. Total 243 patients in the BMI ≥ 40 kg/m2 group and 2813 patients in the BMI < 40 kg/m2 group were identified. There was no difference in VTE incidence between the two groups. However, a strong linear association was found showing as BMI increased so did the rate of VTE incidence. Morbidly obese patients had longer hospital (17 vs. 14 days, P = 0.016) and ICU length of stay (10 vs. 8 days, P = 0.007). After controlling Padua score, logistic regression analysis revealed the odds of VTE increased by a factor of 1.026 for each one-unit increase in BMI. Additionally, having a BMI ≥ 40 kg/m2 was associated with a greater likelihood of VTE incidence in males (OR 3.92) but not in females. In patients treated with standard dose UFH, morbid obesity does not increase VTE risk overall. However, BMI has a strong linear relationship with VTE incidence and morbid obesity is more likely associated with greater hospital and ICU length of stay.