• John Y S Kim, Nima Khavanin, Aksharananda Rambachan, Robert J McCarthy, Alexei S Mlodinow, Gildasio S De Oliveria, M Christine Stock, Madeleine J Gust, and David M Mahvi.
• Department of Surgery, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.
• JAMA Surg. 2015 Feb 1; 150 (2): 110-7.

ImportanceThere is a paucity of data assessing the effect of increased surgical duration on the incidence of venous thromboembolism (VTE).ObjectiveTo examine the association between surgical duration and the incidence of VTE.Design, Settings, And ParticipantsRetrospective cohort of 1,432,855 patients undergoing surgery under general anesthesia at 315 US hospitals participating in the American College of Surgeons National Surgical Quality Improvement Program from 2005 to 2011.ExposureDuration of surgery.Main Outcomes And MeasuresThe rates of deep vein thrombosis (DVT), pulmonary embolism (PE), and VTE within 30 days of the index operation. Surgical duration was standardized across Current Procedural Terminology codes using a z score. Outcomes were compared across quintiles of the z score. Multiple logistic regression models were developed to examine the association while adjusting for patient demographics, clinical characteristics, and comorbidities.ResultsThe overall VTE rate was 0.96% (n = 13,809); the rates of DVT and PE were 0.71% (n = 10,198) and 0.33% (n = 4772), respectively. The association between surgical duration and VTE increased in a stepwise fashion. Compared with a procedure of average duration, patients undergoing the longest procedures experienced a 1.27-fold (95% CI, 1.21-1.34; adjusted risk difference [ARD], 0.23%) increase in the odds of developing a VTE; the shortest procedures demonstrated an odds ratio of 0.86 (95% CI, 0.83-0.88; ARD, -0.12%). The robustness of these results was substantiated with several sensitivity analyses attempting to minimize the effect of outliers, concurrent complications, procedural differences, and unmeasured confounding variables.Conclusions And RelevanceAmong patients undergoing surgery, an increase in surgical duration was directly associated with an increase in the risk for VTE. These findings may help inform preoperative and postoperative decision making related to surgery.

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