UC Davis Research Advances Efforts to Prevent Venous Thromboembolism


Key Points

  • UC Davis researchers created a nomogram to help predict an individuals 30-day venous thromboembolism risk.
  • 1.5% of patients experienced a blood clot before discharge, while 0.5% experienced one after discharge.
  • Risk factors associated with increased risk of venous thromboembolism include age, high body mass index, preoperative infection, cancer, and nonbariatric laparoscopic surgery.
  • Splenectomies carried the highest risk for blood clot, while bariatric surgeries had a lower incidence.

New research from the UC Davis Comprehensive Cancer Center, published in the Journal of Surgical Research, may help clinicians determine which patients are at highest risk for postsurgical blood clots in the legs or lungs.

A team led by Robert J. Canter, MD, Associate Professor of Surgery at UC Davis, studied the medical histories of more than 470,000 surgical patients to determine which factors increased their risk of blood clots, or venous thromboembolism. The team then created a nomogram to help clinicians predict an individual’s 30-day venous thromboembolism risk. The results could change clinical practice by providing a more rational approach to preventing dangerous blood clots.

Critical Safety Challenge

Blood clots are a critical safety and quality challenge for hospitals around the nation. While they can be prevented by administering blood thinners, such as heparin, these measures increase the risk of bleeding. To complicate matters, clinicians have had no way of determining which patients are at higher risk for blood clots, forcing them to adopt a one-size-fits-all approach to prevention.

“The standard preventive measure is heparin,” said Dr. Canter. “However, there are many questions surrounding its use: What type of heparin should be administered? What dosage? Should we give it to patients before or after surgery? By identifying patients who are at higher risk for venous thromboembolism, we attempt to answer many of these questions and help to personalize treatment.”

Blood clots of the legs or lungs are a serious surgical complication, which can cause shortness of breath, longer hospital stays and, in rare cases, death. Successful treatment often requires patients to take the blood thinner warfarin for 3 to 6 months after discharge.

Study Design

The researchers combed through the American College of Surgeons National Surgical Quality Improvement database to identify 471,000 patients who underwent abdominal or thoracic surgeries between 2005 and 2010. Their goal was to identify venous thromboembolism events within 30 days of surgery, both in the hospital and after discharge. Venous thromboembolism includes deep-vein thrombosis and pulmonary embolism.

The team considered many patient factors: age, body mass index, gender, race, preexisting conditions, medical history, smoking, and others. The group also factored in different approaches to surgery—abdominal, thoracic, laparoscopic, etc.—as well as the specific procedure type such as gastrointestinal, hernia, bariatric, splenectomy, or lung. They also looked at postoperative complications, as these could affect both the length of stay and blood clot prevention efforts.

“There are a multitude of factors that go into whether a patient is at risk for venous thromboembolism, as well as how to prevent it,” said Dr. Canter. “Prior to this study, no one had ever looked at so many of these factors so comprehensively.”

Variety of Risk Factors

Overall, 1.5% of patients experienced a blood clot before discharge, while 0.5% experienced one after discharge. These rates were very consistent throughout the study years. A variety of factors were associated with increased blood clot risk, including age, high body mass index, preoperative infection, cancer, and nonbariatric laparoscopic surgery. Splenectomies carried the highest risk for blood clot, while bariatric surgeries had a lower incidence. In addition, major complications after surgery raised the incidence of venous thromboembolism after discharge.

Perhaps most significant, the risks indicated by the study deviate sharply from current Joint Commission risk appraisals. For example, based on the study’s findings, a patient with a history of colon cancer who is having his colon partially removed laparoscopically to treat recurrent cancer has a 10% chance of suffering a blood clot. Meanwhile, a patient having an emergency hernia repair has less than a 5% risk. Under current guidelines, however, both patients would be treated as having equal risk. Use of the nomogram to calculate risk could allow clinicians to more precisely respond to each patient’s individual risk factors.

Surprising Results

The UC Davis research produced a couple of surprises. Although high body mass index generally increased risk, the risk did not carry over to bariatric procedures, perhaps because more aggressive measures are often taken to prevent blood clots in bariatric cases. That splenectomies put patients at higher risk for clots was also a surprise, as the researchers expected the procedure would instead expose them to a higher risk of bleeding.

Dr. Canter notes that while hospitals around the nation have been focused for several years on reducing venous thromboembolism, these measures have not reduced its frequency.

“Despite all the attention to eliminating this as a postoperative complication, the numbers have remained static,” he said. “This shows us that the approach needs to be more individualized.”

While these results need to be validated, Dr. Canter believes the data will help clinicians take a more evidence-based approach to administering heparin and reducing the incidence of blood clots.  He says use of the information fits with hospitals’ overall concern about safety, quality and cost. Specifically, these data could help hospitals and clinicians better focus their quality-of-care initiatives, ensuring that incentives and penalties are based on an accurate model of patient risk.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.