If one leg suddenly swells, feels tight and hurts when pressed, get medical care soon; if there is also sudden shortness of breath or chest pain, call 120 (China's ambulance number) at once

In a real emergency, call 911 first, then read this.

Cost

An ultrasound of the leg's blood vessels (lower-limb venous ultrasound) costs one or two hundred CNY.

What you get

The International Cooperative Pulmonary Embolism Registry (ICOPER) enrolled 2,454 patients with confirmed acute pulmonary embolism from 52 hospitals in 7 countries. A pulmonary embolism is a blood clot blocking the pulmonary artery. The death rate from all causes in this group within 3 months was 17.4% (426/2454). The World Health Organization's WRIGHT project: travel of 4 hours or more in a row "roughly doubles" the risk of a clot forming in a vein and traveling to the lungs (venous thromboembolism). But for any one person the chance is still very low, and for sitting without moving for more than 4 hours it is "about one in six thousand." The UK National Health Service (NHS) advises that on a plane, train or car trip of more than 4 hours, you should wear loose clothing, drink plenty of water, avoid alcohol, and get up and walk when you can. In 2021 Cochrane pooled 12 randomized trials in which the passengers' flights were all longer than 5 hours. Among people who wore graduated compression stockings, deep vein thrombosis without symptoms, found only by testing, was about 90% less: OR 0.10, 95% CI 0.04 to 0.25 (confidence range). Of 2,637 people, 50 had it found: 3 who wore stockings and 47 who did not. In these trials, no one died, got a pulmonary embolism or had a clot with symptoms. So whether compression stockings prevent these truly bad outcomes cannot yet be worked out

Notes

When both legs swell together, it is mostly a problem of the heart, liver, kidneys or vein function. One leg swelling suddenly and being clearly thicker than the other is the typical look of a deep vein thrombosis. Those at risk are people on long car or plane trips, people in bed after surgery or a fracture, people in a cast, women around pregnancy and childbirth, people with tumors, and people taking oral contraceptives. When a clot breaks off and blocks the pulmonary artery, it is a pulmonary embolism: sudden shortness of breath, more chest pain on a deep breath, a fast heartbeat, dizziness and coughing up blood (hemoptysis). At this point call 120 directly. The 17.4% is the death rate among confirmed pulmonary embolism cases, not the risk of "a swollen leg means this much danger," so don't frighten yourself with this figure. The WHO study did not test how to prevent it. It only mentions flexing the ankles up and down and moving the calves while seated, not wearing tight clothing on the trip, and asking a doctor before you leave if you have questions. The compression stocking trials also included high-risk passengers, but they only looked for small clots without symptoms, so if you have risk factors, ask your doctor first about whether to wear them.

Evidence grade

B : Supported by research but without a precise number, or based on small or single studies.

Sources

1. Goldhaber SZ, Visani L, De Rosa M (1999). Acute pulmonary embolism: clinical outcomes in the International Cooperative Pulmonary Embolism Registry (ICOPER). Lancet, 353(9162), 1386-1389. https://doi.org/10.1016/S0140-6736(98)07534-5
2. WHO (2007). Study results released on travel and blood clots. https://www.who.int/news/item/29-06-2007-study-results-released-on-travel-and-blood-clots
3. NHS. DVT (deep vein thrombosis): "If you're travelling for 4 hours or more by plane, train or car" "wearing loose clothing" "drinking plenty of water" "avoiding alcohol" "walking around when possible". https://www.nhs.uk/conditions/deep-vein-thrombosis-dvt/
4. Clarke MJ, Broderick C, Hopewell S, Juszczak E, Eisinga A (2021). Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database of Systematic Reviews, 4, CD004002. https://doi.org/10.1002/14651858.CD004002.pub4

Translated from the Chinese original. Original book, section 13, tip 11. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer