Blood Clots and Long Distance Air Travel

By Michael A. Mignardi

As a fellow runner, I am compelled to tell my story. In 2011, Dallas had its hottest summer on record with over 70 days above 100 degrees Fahrenheit. Most of my 5 am runs that summer started above 80 degrees with a few above 85. In mid-September 2011, I developed a blood clot in my entire left leg and spent seven days in the hospital. Like most runners, I always felt my pastime was a great way to help stay healthy and avoid any major illnesses

  • The typical risk factors for forming a blood clot are:
  • An injury or surgery
  • Pregnancy
  • Birth control pills
  • Smoking
  • Being overweight
  • Over the age of 60
  • A family history of DVT

Because of my overall health and lifestyle, my doctors quickly ruled out the above risk factors and focused on questions centered around any recent long haul air flights or car trips.  During long haul flights, there is some indication that 3-5% of air travelers develop blood clots.  Accurate statistics in this area are not stellar.  However, even if the onset of a DVT during a long haul flight is less than 1%, it is still very important to pay attention to this.

If a blood clot does form, it will typically be in the leg.  While the above mentioned risk factors are important items to pay attention to, there are other factors that can contribute to the formation of blood clots during an air flight:

  • Dehydration:
    • Low oxygen, low humidity (dry air), and low cabin pressure at high elevations have a dehydrating effect. Dehydration, in turn, can make your blood more viscous, thus reducing blood flow.
  • Immobility:
    • During prolonged periods of inactivity, the effects of gravity make it difficult for the blood in the veins of the legs to return to the heart. Blood can pool in the legs.  More experienced traveler will observe that some passengers will complain that their feet swell on these long haul air flights.

There was another finding that caught my eye. About 85% of individuals who do develop blood clots on long-haul flights are athletes—usually endurance athletes (Airhealth.org).  One key factor which makes athletes more susceptible to blood clots is their lower resting heart rate which, by definition, results in reduced blood flow. In addition, these types of athletes tend to be perpetually dehydrated which can be exacerbated further by air travel.

Knowing these potential causes of a DVT during a long haul flight is beneficial as there are many things that you can do to prevent a blood clot from forming during air travel.

  • Dress in loose-fitting clothes and shoes.
    • Socks or garments should not have banded constriction.
  • Consider wearing a graded compression sock.
    • Studies show that compression socks do help in the prevention of a DVT.
    • These socks exert more pressure near the bottom of the leg and less pressure near the knee. The higher pressure near the bottom of the leg increases the blood velocity to help reduce the incidence of venous stasis or blood pooling.  They also reduce and help prevent swelling.
    • Many of my work colleagues now wear compression socks during long haul flights.
  • Stay well hydrated.
    • Drink an electrolyte balanced drink – not just water.
    • Do not drink large amounts of dehydrating beverages: Alcohol or coffee.
  • Exercise your legs and feet every chance you can (e.g. every 20 minutes).
    • When you are sitting, try moving your ankles around and going up and down on your tiptoes (a bit like mini leg-raises).
    • Activity of the calf muscles is needed to contract and pump blood up the legs. Your calves are a great and important muscle for helping pump blood from the lower leg.
    • Get up and move around as often as you can.

My intent with this is to not cause any type of panic with those who travel.  I simply want you to be aware of this and take as many precautions as possible to take care of yourself, family and friends during long haul flights.

** Zensah recommends working directly with a medical professional to properly treat and deal with any issues concerning blood clots and any other medical questions / concerns. ***