RODALE NEWS, EMMAUS, PA—People who have recently undergone surgery are at high risk of developing potentially fatal blood clots (deep-vein thrombosis, or DVT) while flying, according to a recent review published in the medical journal The Lancet.

THE DETAILS: Previous research found that long-haul flights of more than 8 hours could raise your risk of a dangerous blood clot fourfold. In this review, researchers concluded that undergoing a major surgical procedure (including hip and knee surgery) within 6 weeks of air travel puts you at an even higher risk. When you’re sitting down on a long flight, the blood circulation in your legs is cut by two-thirds, and your blood starts pooling in your calves, making a clot more likely. Should a clot break off and get stuck in a critical artery, the result can be fatal. Surgery patients may be at greater risk than healthy fliers because they’ve already spent some time being immobile, and may not be able to move during the flight.

Another health threat for postsurgical fliers is lack of oxygen. “After surgery, the body’s oxygen requirements go up,” explains study coauthor Mark Gendreau, MD, senior staff physician and vice chair of emergency medicine at Lahey Clinic in Burlington, MA. Because of pressure changes in airplanes, he says, it’s harder for the body to get enough oxygen. Healthy people may not notice the difference, but surgery patients could come up short when they need it the most.

WHAT IT MEANS: Know how to protect your health when you fly—particularly if you’ve had surgery or are at increased risk for health problems.

Follow these strategies to keep your body safe in flight: