Flying long distance can be risky for people who are predisposed to blood clots. If they’ve been previously infected with COVID-19, this risk dramatically increases. 

According to the Centre for Disease Control (CDC), a long-haul flight that is four hours or more can increase one’s risk of developing venous thromboembolism (VTE), a condition when blood clots form in the veins.

Studies show that passengers of long-haul flights are three times more at risk for developing blood clots even several weeks after their flight, compared to the rest of the population.

“The prolonged period of sitting and limited movement on an airplane, or any other type of vehicle, can cause blood circulation to slow down or stop, leading to blood clots. Flying carries an increased risk, as the inside of an aircraft is a low oxygen environment. Being in this environment for more than a few hours can cause one’s veins to become inflamed, thus making one more prone to developing a blood clot,” explains Dr Sriram Narayanan, Senior Consultant Vascular and Endovascular Surgeon, The Harley Street Heart and Vascular Centre, Gleneagles Hospital.

Dr Sriram Narayanan, Senior Consultant Vascular and Endovascular Surgeon, The Harley Street Heart and Vascular Centre, Gleneagles Hospital.

The link between COVID-19 and VTE

The possibility of developing blood clots during long-distance travel has always been present, but COVID-19 has dramatically increased this risk.

“COVID-19 is an illness that causes inflammation of the arteries and veins, so patients who have been previously infected are at a higher risk of developing blood clots. Since a vast majority of us have been infected by the virus at some point, the risk of developing blood clots on a long-haul flight today is significantly higher compared to the pre-COVID-19 era,” says Dr Sriram.

A recent Swedish study found an increased risk of Deep Vein Thrombosis (DVT) up to three months after a COVID-19 infection, Pulmonary Embolism (PE) up to six months after, and a bleeding event up to two months post-COVID-19.

Researchers have found that patients with even mild COVID-19 who were not hospitalised, are at an increased risk of DVT and PE. Risks were also found to be highest in patients who were infected with more severe COVID-19 during the first wave of the pandemic, compared to the subsequent waves.

“This could be explained by improvements in treatments and better vaccine coverage after the first wave,” adds Dr Sriram.

DVT and PE: signs and symptoms

DVT happens when a blood clot forms in the deep vein of the leg or arm, due to prolonged immobility or lack of movement. PE occurs when a clot breaks off and travels through the bloodstream to the lungs, through the heart.

“This is a dangerous and potentially life-threatening condition, as the clot can block a blood vessel in the lungs, reducing oxygen absorption, and pose additional strain on the heart. This can lead to sudden death from a cardiac arrest,” says Dr Sriram.

The most common symptoms of DVT on the leg or arm are:

  1. Swelling of the leg or arm
  2. Pain or tenderness that can’t be explained
  3. Skin that is warm to the touch
  4. Redness of the skin

Some warning signs of PE may include:

  1. Difficulty breathing
  2. Faster than normal or irregular heartbeat
  3. Chest pain or discomfort, which worsens with a deep breath or when coughing
  4. Coughing up blood
  5. Very low blood pressure, light-headedness, or fainting

“Anyone who exhibits the above symptoms should head to the nearest hospital or consult a vascular specialist immediately,” advises Dr Sriram.

Unfortunately, about half of the people with DVT and PE don’t exhibit any symptoms at all.

Tips for preventing blood clots while traveling

Fortunately, there is no need to cancel travel plans just yet. There are several ways to minimise the risk and prevent the formation of blood clots while traveling:

  1. Know what to look for. Be aware of your potential risk and be alert to the signs and symptoms of DVT and PE.
  2. Get moving. During the journey, move and stretch your legs frequently, and exercise your calf muscles to improve blood flow. A simple exercise that can be done is to extend your legs straight out and flex your ankles multiple times, pulling your toes toward you. This can help improve the blood flow in your legs.
  3. Consult with your doctor. If you are on anticoagulants (blood thinners), seek advice prior to your flight and follow your doctor’s recommendations on medication use. You may also want to check with your doctor if prescription compression stockings could work for you. These must be medically measured for each individual.
  4. Get risk-assessed prior to flying. If you think you may be at increased risk for blood clots, particularly if you have been recently infected with COVID-19, severe or otherwise, or if a family member has a history of blood clots, you can inquire about undergoing a formal risk screening for DVT with a vascular specialist. This is especially recommended for frequent flyers.