Blood clots can serve a lifesaving function, but they also can be deadly if they form when a person has been immobile for a long period of time. The problem is most common on a long plane flight or car trip when people might be sitting in the same cramped position for several hours.
This week on “Take Care,” we talk to Dr. Menaka Pai, a hematologist at the Hamilton General Hospital in Hamilton, Ontario, about why blood clots form and why they can put your life at risk. Pai is also an executive member of the organization Thrombosis Canada.
Blood tends to clot if a person is immobile and not moving their legs naturally. Pai says it’s the movement of the ankles and knees that keeps blood flowing through the legs.
There are two kinds of blood clots that can form inappropriately. The first is deep vein thrombosis, or DVT, which generally forms in a person’s limbs. A pulmonary embolism, or PE, forms in a major artery and travels to the lungs. A PE can be life threatening because it makes it hard for the body to pump blood.
So why are airline travelers and people in similar circumstances at risk for forming a blood clot? Pai says there are several factors, but by far the biggest factor is not being able to move around and keep the blood moving.
“When we walk around normally, movement at our ankles and our knees, it keeps the blood flowing nicely through the veins. But when that blood stops flowing, it has a tendency to clot. And unfortunately, clots that form inappropriately like that, can cause a blockage in blood movement,” said Pai.
Pai said other factors that could contribute to forming a blood clot when sitting for long periods of time include a knee that’s bent for too long, the pressure of the seat against the leg, wearing restrictive clothing, and perhaps dehydration. All of those factors can add to your blood thickening and then clotting. Changes in air pressure and low humidity are also factors that are suspected to have an impact.
Pai does note, however, that there are not large, well-designed studies about why blood clots form or how many blood clots form in all of these circumstances.
But why don’t blood clots form when you’re sleeping?
“Unlike in sleep, where we naturally move around a little bit throughout the night, whether we notice it or not, you’re not really doing that when you’re sitting immobile,” said Pai.
And Pai says scientists do know that generally the length of travel where a danger of clots occurs is greater than six to eight hours without a lot of movement.
The best prevention for forming blood clots is to move your legs frequently. During air travel, if it’s safe, Pai recommends getting out of your seat every two to three hours to stroll up and down the aisle one or two times as sufficient. If you’re driving, stopping at a rest stop and walking a bit every two to three hours should be enough.
Pai says standing up is not enough. You need the movement of your hips, knees and ankles to really get the blood moving. She said doing some leg exercises while seated is better than nothing, but the act of walking is best.
It’s also good to know if you’re particularly at risk for forming blood clots and what the warning signs are.
Risk factors include age (people over age 40), obesity, and other medical conditions like cancer. High hormone levels can put women on birth control pills, and women who are pregnant or post-partum at greater risk.
Warning signs for a DVT in your leg or arm are pain or tenderness, a swollen limb, warm skin and tenderness.
If a PE has formed a person may experience difficulty breathing, a fast heartbeat or a sharp pain in the chest that gets worse when breathing.
A lot of small blood clots can go away on their own, but as soon as these symptoms show up, Pai says it’s imperative to seek medical treatment.
A CT scan can confirm whether or not a blood clot is present. Pai says typically a patient would be given blood thinners that are anti-coagulants. She says usually with three months of treatment, most clots resolve themselves well.
Pai also says to keep in mind that the overall risk for forming a blood clot while traveling by air or car is low -- only between one to 10 people per 2 million people will have this happen.