Risk of blood clots after surgery is higher and lasts longer than thought

Studies have shown that the risk of developing blood clot after major surgery is high but a new study pubished in BMJ Online First on 4 December found that this risk is higher and continues for up to 3 months after surgery.

The research was a large prospective study that tracked 947,454 women, average age 56, who were diagnosed with venous thromboembolism through the NHS breast screening programme between 1996 and 2001. The reserachers checked hospital admission and death records, followed for an average of 6.2 years and compared the risk of blood clots for those who did not have surgery with those who did have surgery.

The researchers found that within 6 weeks post operation, women who had day case surgery were 10 times more likely to have blood clots than those who had no surgery. The risk for those who had surgery in the hospital were nearly 70 times higher. At 7 to 12 weeks after surgery, the risk of blood clots was 6 times higher for the day case surgery group than the no surgery group and 20 times higher for the inpatient surgery group.

They also calculated different risks for different surgery and found that the incidence of blood clots in the 12 weeks after surgey :

• 1 in 45 had developed blood clots after hip or knee replacement;
• 1 in 85 after cancer surgery;
• 1 in 815 after day surgery;
• 1 in 6,200 women who did not have surgery

The researchers warn that the risk of developing blood clot after surgery is higher and lasts for longer than previously thought and suggest that doctors should extend the time that preventive measures such as blood thinning drugs or wearing stockings are used.

Critics say that despite the lack of data on how many of the participants were taking preventive measures, this study is important because it broadens our understanding to current evidence of the risk of potential fatal blood clot after surgery and the findings may have implications for prolonged prophylaxis after surgery.

Source:
Editorial : Cohen TA. Prevention of postoperative venous thromboembolism. BMJ 2009; 339: b4477 (f/t via Athens)
Sweetland S, Green J, Liu B. et al. Duration and magnitude of the postoperative risk of venous thromboembolism in middle aged women: prospective cohort study. BMJ 2009; 339: b4583 ( f/t via Athens)