Backgroud:
Venous Thromboembolism (VTE) is a potentially fatal complication seen in 1.4-5.8% of patients after free tissue transfer to the head and neck (H&N) region. Fixed-dose enoxaparin 30 mg twice daily (BID) is a widely used chemoprophylaxis regimen. However, differences in enoxaparin metabolism based on body weight may influence its efficacy and safety profile. We aim to assess the impact of body-mass-index (BMI) on VTE, hematoma, and vascular compromise rates within 30 days of surgery.

METHODS: A prospective cohort of patients who underwent H&N reconstruction (between 2013-2021) with free tissue transfer and received 30 mg BID enoxaparin post-operatively was reviewed. Demographic data, BMI, comorbidities, smoking status, personal VTE history, family VTE history, Caprini score, and flap type were collected for each patient. BMI was divided into four categories: underweight (<18.5), healthy (18.5 to <25), overweight (25 to <30), and obese (>30). Moreover, The VTE risk in all patients who are deemed to be overweight or obese was assessed. Post-operative adverse events were recorded, including VTE, hematoma requiring intervention, and vascular compromise within 30 days of index surgery. Multivariate logistic regression models were used to evaluate the association between BMI and VTE, hematoma, and vascular compromise, respectively.

RESULTS: 712 (mean age 61 ± 12 years, 33.23% female) out of 917 patients met inclusion criteria. The mean BMI was 26.68 ± 8.20. Venous thromboembolism, hematoma, and vascular compromise rates among all patients were 4.1%, 5.2%, and 6.6%, respectively. VTE rates in patients with BMI < 25 were significantly lower than in patients BMI > 25 (5.8% vs. 2.1%, p= 0.013). The VTE rate was also significantly increased in obese (BMI > 30) patients compared to all other patients (6.7% vs.3.2%, p=0.040). There were no significant differences in hematoma rates in the underweight patients (BMI < 18.5) when compared to all other patients (10.7% vs. 4.7%, p= 0.53). The BMI four categories were not associated with vascular compromise (p = .3889). After adjusting for multiple patient factors, BMI > 25 was independently associated with increased odds of VTE (OR 2.735 95%CI: 1.143-6.543). Body-mass-index outperformed Caprini score to predict post-operative VTE.

CONCLUSIONS: Elevated BMI is associated with an increased risk of VTE after head and neck reconstruction with free tissue transfer. This association may suggest insufficient VTE prophylaxis in this group and a potential indication for weight-based dosing.