After sitting on a plane for several hours, I suddenly died when I stood up. What happened?

Author: Chen Zhong, Chief Physician, Beijing Anzhen Hospital, Capital Medical University

President of the Vascular Surgery Branch of the Chinese Medical Doctor Association

Reviewer: Liu Changwei, Chief Physician, Peking Union Medical College Hospital

There was a case where a passenger suddenly died when he stood up after sitting on a plane for several hours.

The cause of the investigation was that he had been sitting on a plane for a long time without any activities or drinking water, which led to blood clots in the deep veins of his lower limbs. When he stood up, the blood clots broke off and embolized the pulmonary artery, causing pulmonary embolism.

Later, deep vein thrombosis of the lower limbs was also called economy class syndrome.

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Because economy class seats are relatively small, with some having five seats in a row, it is relatively difficult to move around, especially for passengers sitting inside. It is not very convenient to get out, and they are often reluctant to trouble others, so they try not to get out. In order to reduce the urgency of going to the bathroom, they will try to drink less water, or even no water.

In a small space, maintaining one posture without moving and having a very small range of movement will slow down the blood flow. If you do not drink water, the blood viscosity will increase and concentrate, making it easy to form blood clots, so it is called economy class syndrome.

1. Why are deep veins in the lower limbs prone to thrombosis?

The veins of the lower limbs are divided into two categories. One category is the superficial veins that can be seen on the surface, such as the great saphenous vein and the small saphenous vein. These can be seen on the surface, especially when the person is thin. The light blue color of the epidermis can be seen, and even these blood vessels protruding from the surface of the body are generally called superficial veins.

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Deep veins often run alongside arteries in the muscle spaces and have the following characteristics: first, they are located relatively deep; second, their diameter is significantly thicker than that of superficial veins, and the overall blood flow rate is affected by valves.

The valves of a normal person should be one-way valves. Due to the effect of gravity and the low pressure of the veins, which is only about 6-8 cm of water column, unlike the arteries, which have a high-pressure squeezing effect to overcome gravity. It is often difficult for venous blood flow to overcome gravity, so normal people have many pairs of venous valves in their lower limbs to prevent blood from flowing back or reverse perfusion. Through muscle activity, the blood is squeezed upwards in streams, and the valves hold the blood flow, which cannot flow back, so it can only flow in one direction, just like a door can only be opened in one direction.

If there is a problem with the valve, such as it is not closed tightly, or the blood vessel wall is damaged and the valve cannot close, the amount of blood in the legs will increase, causing venous reflux obstruction and blood clot formation.

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In addition, long-term inactivity and dehydration lead to blood concentration, which is also very important for thrombosis. There are also changes in hormone levels, such as taking birth control pills, which lead to changes in the coagulation mechanism; increased pelvic pressure, such as in the middle and late stages of pregnancy, pelvic tumor compression, etc., which are all high-risk factors that easily cause thrombosis.

In general, thrombosis is closely related to three major factors: first, changes in the coagulation mechanism (hypercoagulable state), second, increased venous pressure and slower blood flow, and third, damage to the blood vessel wall (which easily leads to thrombosis).

Deep vein thrombosis in the lower limbs occurs in the deep veins, which have thick blood vessels and a relatively large amount of thrombus formation. Therefore, once the thrombus breaks off, the chance of pulmonary embolism and life-threatening consequences is very high.

Relatively speaking, the incidence of pulmonary embolism in superficial veins is generally low, so generally speaking, more attention is paid to deep vein thrombosis in the lower limbs.

2. How to prevent deep vein thrombosis in the lower limbs?

How can people who sit, stand or lie in bed for a long time prevent deep vein thrombosis in the lower limbs?

Several ways:

If you can take the initiative to exercise, such as taking a long-distance trip in economy class, especially on international flights, you should at least keep a certain amount of water even if you don't stand up and move around. The humidity in the cabin is very low due to air convection, and it is easy to lose water. If you don't replenish water in time, it is easy to cause blood concentration.

Even if you don't stand up and move around, you can do some active foot dorsiflexion and extension reciprocating movements, or squeeze the thigh and calf muscles with your hands frequently, or do some leg flexion and extension movements, straighten your legs, then adduct them, straighten them again, then adduct them again, or do some toes-raising movements.

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For example, when playing mahjong and sitting at the table for four or five hours, it is best to get up and move around for an hour, and the longest time should not exceed two hours.

For people who stand in a fixed posture for a long time, such as surgeons, doormen, etc., it is generally not recommended to stand in a fixed posture for more than two hours. They should move around or take a break.

So if you can move on your own, you should increase some active exercises, such as stand up and walk around, stretching and flexing your legs, and curling your toes. If that doesn't work, you can just rub your legs with your hands.

For those who cannot actively exercise on their own, such as those who are forced to stay in bed, those who cannot move after a fracture or major surgery, or those who are unconscious or in a coma, passive methods can be used, such as family members helping to do some reciprocating flexion and extension exercises of the legs and feet, or some necessary muscle compression exercises.

In addition, there is a kind of passive exercise that relies on the leg pressure assist device, which can be put on the leg. Through the mechanical squeezing of pressure from the foot to the calf and then to the thigh (that is, from the distal end to the proximal end), it can achieve the same effect as voluntary exercise.

Whether it is active exercise or passive exercise, they both help blood return through external mechanical squeezing and prevent venous thrombosis caused by blood stasis due to long-term inactivity.