Long-haul flights, length of time under anesthesia increase risk of developing blood clots

May 31 2005

The prolonged immobility of flight passengers during long-haul air travel increases the risk of developing blood clots, which could prove fatal especially to people whose travel occurs just prior to major surgery, medical researchers report in the current issue of Mayo Clinic Proceedings.

"At medical institutions where patients are traveling a great distance for surgery, physicians should consider it as an additional risk factor for postoperative blood clots in the veins," says Juraj Sprung, M.D., Ph.D., a Mayo Clinic researcher in the Department of Anesthesiology at Mayo Clinic in Rochester. The study was conducted by Dr. Sprung and others.

Dr. Sprung advises that physicians consider taking extra preventive measures with the patient during the flight and during and after the surgery.

The risk of blood clots prior to surgery and after surgery is explored in several articles in the current issue of Mayo Clinic Proceedings, providing patients and clinicians with valuable advice to consider.

Dr. Sprung says that the study was prompted after a 37-year-old man, who had traveled about 4,800 miles in a transatlantic flight before surgery, died from a pulmonary embolism after the surgery.

The formation of a blood clot within one of the large, deep veins of the pelvis or lower limbs, often in the deep veins of the calf, thigh, knee or pelvis, is referred to as deep vein thrombosis (DVT). A pulmonary embolism can form when the blood clot breaks into smaller pieces, floats in the blood and becomes lodged in the blood vessels supplying the lungs, which may result in sudden death.

Dr. Sprung and colleagues analyzed patient information at Mayo Clinic and found that of 181,765 patients who underwent operations between 1998 and 2002, a total of 3,736 lived outside of the United States, Canada and Mexico and traveled on average more than 5,000 miles prior to surgery. These long-haul travelers experienced over 30-times-higher incidence of dangerous blood clots or pulmonary embolisms within 28 days of surgery compared to the surgical patients who either did not travel or traveled within North America. The facts that an average age of these patients was much lower, and that blood clots occurred much earlier after surgery suggest that long distance travel before surgery represents an increased risk for dangerous clots (DVT) and its severe complications such as pulmonary embolism.

Dr. Sprung notes increased awareness among airlines and other agencies about the risks of blood clots forming during long-haul air travel, but additional measures may be needed for those who travel to have the surgery. He says several factors contribute to the risk of blood clots forming in the veins, including long periods of immobility during flight, restriction of leg veins due to compression on the legs from the edge of the seat, and possibly dehydration due to decreased fluid intake or excessive use of alcohol during the flight.

The authors recommend that patients traveling long distances prior to major surgery be told of the potential for increased risk of complications with blood clots. During the flight, patients can take preventive measures by staying well hydrated, exercising and wearing elastic compression stockings. High-risk patients also can benefit from prescribed medications to prevent the problems.

Authors of the study include Dr. Sprung, Ognjen Gajic, M.D.; David Warner, M.D.; Paul Decker; Rimki Rana, M.D., all of Mayo Clinic; and Denis Bourke, M.D., of the University of Maryland and the Baltimore Veterans Affairs Medical Center.

In a second study in Proceedings, researchers noted a marked association between the duration of anesthesia for patients undergoing hip or knee replacement surgery and blood clots in the veins after surgery.

Analysis of the patient data suggests a threshold of anesthesia duration that increased the odds of a patient having blood clots in the veins. The information indicates that 3.5 hours (210 minutes) is the threshold. The longer duration of anesthesia is usually related to how long it takes the orthopedic surgeon to perform a major joint replacement. It makes sense that this raises the risk of blood clots in the veins because the patient is supine and blood pools in the areas.

"Our findings may apply to other types of surgical procedures as well," says Daniel Brotman, M.D., the lead author of the paper and director of the hospitalist program at Johns Hopkins Hospital.

Dr. Brotman and his colleagues recommend further study to examine the risk and prevention of postoperative blood clots in the veins and the relation to anesthesia duration. Approximately 500,000 patients undergo total joint arthroplasty, either hip or knee, in the United States each year. Patients are treated with drugs to combat the blood clots in the veins during surgery, but up to 38 percent may still develop the condition. And although they are small clots, approximately 5 percent result in a fatal pulmonary embolism.

In an editorial in the same issue of Proceedings, Samuel Goldhaber, M.D., of the Cardiovascular Division of Brigham and Women's Hospital, Harvard Medical School, writes that both studies are good reminders of the perils of postoperative deep vein thrombosis and pulmonary embolisms with general and orthopedic surgery.

"Despite the effectiveness of preventive measures that can be taken with patients for blood clots in the veins, it remains underused," says Dr. Goldhaber. Protocol-driven preventive care is definitely cost-effective and will serve patients well, he says.