Longer surgeries raise blood clot risk

"Minute by minute, hour by hour, the trend is much more pervasive and consistent than any of us believed it could be," says senior study author John Kim. "It was true across all procedures, specialties, and hospitals." (Credit: iStockphoto)

The longer a surgery lasts, the higher the risk of a life-threatening blood clot, a new large-scale study of more than 1.4 million patients reports.

The findings will help surgeons and patients better understand the potential risk of procedures and may also promote more aggressive preventative measures such as giving a patient blood thinner to reduce the risk of clots and limiting longer surgeries by splitting up procedures.


The link between longer surgical procedures and blood clots, or venous thromboembolism, has been widely accepted but until now has been based on anecdotal evidence and had not been rigorously quantified.

More than 500,000 hospitalizations and 100,000 deaths are associated each year with blood clots.

Venous thromboembolism is designated by the US Department of Health and Human Services as a “never event,” because it is considered an unacceptable outcome of surgery.

“Minute by minute, hour by hour, the trend is much more pervasive and consistent than any of us believed it could be,” says senior study author John Kim, associate professor of surgery at Northwestern University. “It was true across all procedures, specialties, and hospitals.”

Slower blood flow

Blood clots in surgery are a risk for the same reason they are on long plane rides, says coauthor Nima Khavanin, a student in the Feinberg School of Medicine.

“If you’re not moving, your blood flow slows down, and your blood cells are more prone to clumping and forming a clot. This can cause a fatal pulmonary embolism.”

For the study published in the JAMA Surgery, 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 clots. The study included more than 1.4 million patients who had surgery under general anesthesia at 315 US hospitals from 2005 to 2011.

In the most common surgeries—including gall bladder removal, appendix removal, and gastric bypass for weight loss—every additional hour of surgery duration resulted in an 18 to 26 percent increase of developing a clot.

Patients that underwent the longest surgeries had a 50 percent increase in the odds of developing a blood clot compared to the shortest, regardless of the surgical procedure.

The overall impact is greatest in longer, more invasive operations such as heart surgery, but the relationship between operative time and blood clots exists regardless of the procedure or surgical specialty and even applies to shorter procedures such as laparoscopic gall bladder or appendix removal.

The findings may affect how surgeons plan procedures.

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

Source: Northwestern University