The association between surgical duration and venous thromboembolism in outpatient surgery: A propensity score adjusted prospective cohort study

Background: Outpatient surgeries account for 60-70% of all procedures. Increased surgical duration has been demonstrated to be an independent risk factor for the development of venous thromboembolism (VTEs) after inpatient surgeries. In contrast, it is currently unknown if surgical duration increases the risk of VTEs for outpatient surgeries. Materials and methods: The 2005 through 2016 NSQIP Participant Use Data Files were queried to extract all patients scheduled for outpatient surgery. A z-score for surgical duration was calculated for each procedure to allow for standardization across surgeries of expected shorter or longer duration. The primary outcome measured was incidence of VTEs within 30 days of surgery. Results: A total of 3474 patients out of 1,863,523 (0.19%) had a VTE. After adjusting for confounding factors, the first and fifth quintiles compared to the middle quintile had odds ratios (ORs) of 0.75 (95% CI 0.68, 0.80) and 1.43 (95% CI, 1.35%-1.52%), respectively, P < 0.001. Patients who developed VTEs were more likely to be readmitted to the hospital, OR (95%CI) of 51.9 (48.0-56.2), C statistic = 0.67. Conclusion: Surgical duration is associated with the development of VTEs after outpatient surgery. While the overall incidence of VTE is low and does not require generalized prophylaxis, clinical practitioners should consider prophylaxis for patients undergoing outpatient surgery performed with excessive time compared to the average surgical procedure duration.