Objective: To identify independent predictors of 30-day venous thromboembolism (VTE) events requiring treatment after outpatient surgery.
Background: An increasing proportion of surgical procedures are performed in the outpatient setting. The incidence of VTE requiring treatment after outpatient surgery is unknown.
Methods: Prospective observational cohort study using the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database from 2005 to 2009. Adult patients who had outpatient surgery or surgery with subsequent 23-hour observation were included. The main outcome measure was 30-day VTE requiring treatment. Patients were randomly assigned to derivation (N = 173,501) or validation (N = 85,730) cohorts. Logistic regression examined independent risk factors for 30-day VTE. A weighted risk index was created and applied to the validation cohort. Stratified analyses examined 30-day VTE by risk level.
Results: Thirty-day incidence of VTE for the overall cohort was 0.15%. Independent risk factors included current pregnancy (adjusted odds ratio [OR] = 7.80, P = 0.044), active cancer (OR = 3.66, P = 0.005), age 41 to 59 years (OR = 1.72, P = 0.008), age 60 years or more (OR = 2.48, P < 0.001), body mass index 40 kg/m2 or higher (OR = 1.81, P = 0.015), operative time 120 minutes or more (OR = 1.69, P = 0.027), arthroscopic surgery (OR = 5.16, P < 0.001), saphenofemoral junction surgery (OR = 13.20, P < 0.001), and venous surgery not involving the great saphenous vein (OR = 15.61, P < 0.001). The weighted risk index identified a 20-fold variation in 30-day VTE between low (0.06%) and highest risk (1.18%) patients.
Conclusions: Thirty-day VTE risk after outpatient surgery can be quantified using a weighted risk index. The risk index identifies a high-risk subgroup of patients with 30-day VTE rates of 1.18%.