According to researchers from Northwestern University's Feinberg School of Medicine, risks of blood clots forming are directly proportional to the length of surgeries. This means that those under the knife longer are at higher risks of developing blood clots compared to those who underwent shorter procedures.

Published in the journal JAMA Surgery, the study involved data from the National Surgical Quality Improvement Program of the American College of Surgeons. Researchers examined data available, focusing on associations between blood clots forming and the length of a surgery. Over 1.4 million patients were assessed for the study, all of whom underwent surgery between 2005 and 2011 across 315 hospitals in the United States.

A total of 13,809 patients who developed venous thromboembolisms (VTE) were discovered, while 10,198 experienced deep vein thrombosis and 4,772 developed pulmonary embolisms. Compared to surgery of average length, patients with the longest procedures experienced a 1.27-fold increase in risks of developing VTE.

"Minute by minute, hour by hour, the trend is much more pervasive and consistent than any of us believed it could be. It was true across all procedures, specialties and hospitals," said John Kim, M.D., Dermatology and Surgery-Plastic associate professor and the study's senior author.

Nima Khavanin, a third-year medical student and one of the co-authors of the study, explained that blood clots during surgery are a risk in the same way as they are on long plane rides. It's because if a person is not moving, their blood flow starts to slow down. With blood flow stunted, blood cells develop the tendency to clump together, forming a clot. This is what leads to fatal pulmonary embolisms.

In the most common surgical procedures, which include gastric bypass, appendix removal and gall bladder removal, each extra hour spent on surgery resulted in a between 18 and 26 percent increase in risks of developing blood clots. Patients who logged the longest surgery times increased their risks by 50 percent!

The researchers believe the study may have an effect on how surgeons plan their procedures, highlighting the need to better assess the practice of combining surgeries.

"If you know longer surgeries have a higher risk, depending on the variables, splitting up those surgeries may be the best option," said Kim.

Other authors include: David Mahvi, M.D.; Madeleine Gust; M. Christine Stock; Gildasio De Oliviera Jr., M.D.; Alexei Mlodinow; Robert McCarthy, PharmD; and Aksharananda Rambachan.

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