The latest studies show you have a higher risk of developing dangerous blood clots when you fly if you’ve recently recovered from Covid-19. And if the blood clots travel to your lungs, they can be fatal. Here’s what you need to know to protect yourself
Flying off on holiday, or for work is not the same today. The pandemic has changed everything. And some experts fear that as more Singaporeans return to traveling long-distance, we’ll see more dangerous blood clots forming deep inside the legs.
Deep vein thrombosis (DVT) is when a blood clot forms in a blood vessel deep inside your body, far away from your skin, that carries blood toward your heart. This mainly happens in your legs and pelvis. It can also happen in your arms, though not nearly as often.
If part of the clot breaks off and travels to the lungs, it can cause a sudden blockage of the arteries in the lung, or what’s called Pulmonary Embolism (PE). This can be fatal. Some 4-14 per cent of people with DVT are at risk of dying of PE.
We’ve known for a while that blood clots are more common in passengers who’ve taken long-haul flights. Long-haul passengers are three times more at risk for blood clots for several weeks after their flight, compared to the rest of the population, with two to 10 per cent of passengers showing signs within 48 hours of landing.
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And now it turns out that the risk of DVT thus increases significantly for passengers who have been infected with COVID-19 and then recover, and take a long-haul flight, or even a series of short flights.
A study from Sweden found an increased risk of DVT up to three months after a COVID-19 infection, and a higher risk of PE up to six months after.
Researchers also found that patients with even mild COVID-19 – who were not hospitalised – were still at an increased risk of DVT and PE. But risks were highest in patients who were infected with more severe COVID-19 during the first wave of the pandemic, compared to the second and third waves.
Fortunately, there are ways to assess if you are at an increased risk of DVT before your flight, and there are ways to prevent blood clots from forming while you are traveling. To find out more, we spoke with Dr Sriram Narayanan, Senior Consultant Vascular Surgeon, The Harley Street Heart & Vascular Centre;
Deep Vein Thrombosis (DVT) happens when a blood clot forms in a vein deep inside your legs. You can get a DVT when you sit or lie down for prolonged periods of time, such as during a flight or if you are on bed rest after surgery. This is because when you don’t move enough, blood in the veins of the legs and arms flows back more slowly to the heart. When blood pools in the veins it can cause blood clots to form.
When a clot breaks off and travels through your bloodstream to your lungs through the heart, it can cause a Pulmonary Embolism. This is a dangerous and potentially life-threatening condition because the blood clot can block a blood vessel in the lungs. Less oxygen is absorbed by the lungs and strains your heart.
COVID-19 is a complex illness and causes a range of symptoms, from mild to potentially life-threatening. One of the commonly reported symptoms of COVID-19 is abnormal clotting of blood.
Dr Sriram Narayanan explains, “COVID-19 is primarily an infection of the lining of the blood vessels. The COVID-19 virus enters your body through the lungs. The spike protein attaches to the lining of the blood vessels, causing the blood vessels in the lungs to get inflamed. This causes the arteries and veins in your lungs to clot, making it difficult for oxygen exchange to happen.”
A study from Sweden found an increased risk of DVT up to three months after a COVID-19 infection, and a higher risk of Pulmonary Embolism up to six months after.
Dr Sriram Narayanan explains. “Blood clots occur when blood circulation slows or stops, due to limited movement. In addition, the inside of an aircraft is a low oxygen environment. Sitting still in this environment for a few hours can lead to your veins getting inflamed. This makes you more prone to developing blood clots on a long-haul flight.”
Studies show passengers of long-haul flights are three times more at risk for developing blood clots for several weeks after their flight, compared to the rest of the population. This was true even before COVID-19. But COVID-19 significantly elevates the risk of people developing blood clots during or after long-haul flights, or even consecutive short-haul flights.
So if you’re recovered from Covid-19 and you’re planning an airplane trip, try to wait at least two weeks, if you can. And wear medical-grade compression stockings or socks, and speak to your doctor about taking some blood thinners for the trip.
The most common symptoms of DVT are:
- Swelling of the leg or arm
- Pain or tenderness that can’t be explained
- Skin that is hot to the touch
- Redness of the skin
But about half of people with DVT don’t exhibit any symptoms. So also look for these symptoms:
- Difficulty breathing
- Faster heartbeat than normal, or irregular heartbeat
- Chest pain or discomfort, which gets worse when you breath deeply or cough
- Coughing up blood
- Very low blood pressure, light-headedness, or fainting
If you see any of the above symptoms, head to the hospital immediately.
It’s not just Covid-19 that can increase your risk of DVT. Other conditions that affect blood flow within your body can also raise your risk. They include;
- Varicose veins
- Previous DVT or PE
- You’ve recently had major general surgery
- Sitting still, limited movement, or paralysis
- Increased estrogen levels caused by oral contraception, hormone replacement therapy or pregnancy (your risk is elevated up to three months after giving birth)
- Family history of blood clots and clotting disorders
- Cancer, especially if patients have undergone chemotherapy and surgery
- Injury to a vein caused by fractures, muscle injury or major surgery of the hip, pelvis, or legs
- Medical conditions such as heart disease, lung disease and inflammatory bowel disease
- Increasing age
- Obesity
Talk to your doctor if you think you may be at risk for blood clots – particularly if you have been recently infected with COVID-19, severe or otherwise:
- Also speak to your doctor if you or a family member has a history of blood clots. A risk screening for DVT is recommended, especially if you are a frequent flyer.
- On a long trip or flight, move your legs frequently and exercise your calf muscles to improve the flow of blood.
- If you’ve been sitting for a long time, make sure you stretch your legs and flex your ankles multiple times, pulling your toes toward you. This can help improve the blood flow in your legs.
- Consult with your doctor and find out if wearing prescription compression stockings or long socks might work for you.
- If you are on blood thinners (anticoagulants), seek advice from your doctor before your flight and follow your doctor’s recommendations on using your medication.
You can also schedule an appointment with a vascular specialist. Because there are tests you can do before flying that can assess your risk for developing blood clots. They include:
- Light Reflex rheography, which looks at the volume of venous blood returning and how well your calf muscle is pumping blood back to the heart.
- Duplex ultrasonography is the standard imaging test to diagnose DVT or previous silent DVTs.
- Blood screening is helpful in patients with a family history of thrombosis or blood clots.
Anticoagulants (or blood thinners) injections of tablets are the most common treatments for DVT. They prevent a clot from becoming larger so the body can slowly reabsorb it. Doctors can also use several minimally invasive surgical techniques to remove a clot before it reaches the lungs.
Says Dr Sriram Narayanan, “If you have a history of blood clots or have been recently infected by COVID-19, your risk of developing DVT or PE while flying may be elevated. But, this does not necessarily mean you have to cancel all your upcoming travel plans.”
Speak to your doctor to find out how you can prevent blood clots, know what symptoms to look for, and your treatment options.