CHICAGO – The longer surgery lasts, the more likely patients are to develop a life-threatening blood clot.

That’s according to the first large-scale, quantitative national study of the risk across all surgical procedures, published recently in JAMA Surgery. More than 500,000 hospitalizations and 100,000 deaths are associated each year with blood clots, according to background in the article.

The authors from Northwestern University’s Feinberg School of Medicine suggest the results will help hospitals and surgeons better understand the potential risk of procedures. They also emphasize the importance of using aggressive preventative measures such blood thinners to reduce the risk of clots as well as imposing limits on longer surgeries by splitting up procedures.

For the study, researchers analyzed data from the American College of Surgeons National Surgical Quality Improvement Program to look at the association between surgical duration and the incidence of VTE. The study included more than 1.4 million patients who had surgery under general anesthesia at 315 U.S. hospitals from 2005-11.

Results indicate that 13,809 patients (0.96%) had a postoperative VTE; 10,198 patients (0.71%) experienced deep vein thrombosis; and 4,772 patients (0.33%) developed a pulmonary embolism.

Compared with a surgical procedure of average duration, according to the study, patients who underwent the longest procedures experienced a 1.27-fold increase in the odds of developing a VTE, while the shortest surgical procedures had lower odds.

"Minute by minute, hour by hour, the trend is much more pervasive and consistent than any of us believed it could be," said senior study author John Y. S. Kim, MD. "It was true across all procedures, specialties and hospitals."

Surgical time was shown to be a risk factor for VTE in three of the most common procedures – laparoscopic cholecystectomy, appendectomy and gastric bypass.Every additional hour of surgery duration increased the risk of developing a blood clot 18% to 26%, according to the study.

Overall, regardless of the surgical procedure, patients undergoing the longest surgeries had a 50% increase in the odds of developing a blood clot compared to the shortest.

 “There may be times when we have the option of cobbling together a couple of surgeries,” Kim said. “If you know longer surgeries have a higher risk, depending on the variables, splitting up those surgeries may be the best option."