Causes of a pulmonary embolism

Pulmonary embolism is most frequently caused by deep vein thrombosis (syn. phlebothrombosis). It often develops in the deep veins of the leg, especially in people with diseases of the coagulation system or bedridden patients.

However, it can also occur as a result of an inflammatory event or trauma, or if the flow conditions change as a result of heart failure. But also: can significantly increase the risk of clot formation. These clots in the deep veins of the legs can be released by sudden physical exertion, getting up in the morning or during pressor acts ,such as defecation, and are then transported to the lungs by the venous bloodstream system.

This usually happens after a longer resting phase, such as after lying down for a long time or sitting with bent legs, for example in a bus or plane. Other, but rarer, causes include a fat embolism, a lump of fat that displaces a pulmonary artery, which can occur after surgery or open fractures. But air embolism is also possible, which is usually caused accidentally by the doctor laying or pulling central venous catheters.

You can find more information on this topic under: Therapy of a pulmonary embolism

  • Central venous catheters,
  • Chemotherapy,
  • Hormone replacement therapies,
  • Oral contraception especially in combination with nicotine,
  • A pregnancy or
  • Fractures especially of the hip/leg

As soon as the vessels become too narrow for the embolus, the embolus gets stuck, thus clogging the vessel. If it is a very small vessel, clinical symptoms are initially absent. However, if a larger vessel is displaced, the lung can no longer be supplied with blood efficiently in this section, and gas exchange does not occur.

In addition, the reduced blood flow leads to vasoconstriction of the large pulmonary artery (pulmonary contraction). As a result, the pressure load on the right heart increases and the so-called cor pulmonale develops. Due to the reduced oxygen supply and increased dead space ventilation (aeration of lung sections that are not supplied with blood), an acute lack of oxygen, especially of the heart muscle, occurs.

This leads to a reduction in heart function and can ultimately lead to circulatory shock with a drop in blood pressure and an increase in heart rate. A loss of lung tissue (pulmonary infarction) due to the lack of oxygen only occurs in about 10% of all cases. Various factors can lead to the formation of such a blood clot.

One factor is malignant diseases, such as various malignant tumors. Most frequently, an accompanying thrombosis is observed in pancreatic and bronchial tumors, but it can occur in any type of cancer. In tumor diseases, the so-called Virchow’s triad changes, namely the composition of the blood, the blood flow and also the vascular wall.

The change in these components of the vascular system almost always precedes thrombosis. Pulmonary embolism can also occur when the tumor grows into the vascular system and then a fragment of the tumor is flushed into the lung via the vascular system. However, some tumors also release certain signal substances that promote blood clotting.

This quickly leads to the formation of a blood clot, which can then dissolve and cause a pulmonary embolism. Smoking is a significant risk factor for the development of thrombosis and, secondarily, pulmonary embolism. The nicotine contained in cigarettes has a narrowing effect on the blood vessels and at the same time promotes blood clotting.

This means that two factors already come together to promote the formation of a blood clot. In addition, smokers develop deposits on the walls of the blood vessels (plaques) at an early stage, to which blood fats and platelets are attached. This leads to vasoconstriction, which can even lead to vascular occlusion (peripheral arterial occlusive disease).

In the worst case, smokers can lose lower limbs (so-called smoker’s leg) if the lower extremities are less supplied with blood by the constricted or thrombosed vessels. Women who smoke and take the contraceptive pill at the same time are particularly at risk for thromboses and pulmonary embolism (see: Risk of thrombosis with the pill). The sex hormones also promote blood clotting and, in combination with smoking, increase the risk of thrombosis considerably.

Smokers should definitely be informed about this risk.Deep vein thrombosis of the leg is the typical cause of pulmonary embolism. This causes a blood clot to form in a vein in the leg. This is caused by changes in the flow velocity of the blood, changes in the vessel wall and changes in the coagulation system.

Smaller thromboses can proceed without symptoms, while larger thromboses cause the foot on the affected side to be swollen and the affected leg to overheat. A pulmonary embolism occurs when the clot comes loose, is pumped back through the vessels to the heart and from there to the lungs. In the lung, it clogs the blood vessels and can thus trigger a life-threatening embolism.

Pelvic vein thromboses are blood clots that form in a vein (vessel that transports blood towards the heart). They manifest themselves by sudden pain in the groin area as well as pain and swelling in the leg of the affected side. Possible causes are increased coagulability of the blood and changes in the vessel wall.

Just as in deep vein thrombosis, the blood clot may come loose. It is transported with the bloodstream to the heart and from there it is pumped into the lungs, clogging pulmonary vessels and thus triggering a pulmonary embolism. After the operation of a hip or knee prosthesis, affected persons are usually immobile for a longer period of time.

The operated side in particular must not be subjected to any or very little stress at first. Blood, which is pumped from the heart via arteries into the legs, normally flows back to the heart via veins against gravity. The muscle action helps with every step to pump the blood a little bit forward.

For this reason, non-exertion leads to altered flow conditions in the veins and therefore promotes the development of thromboses (blood clots). These can come loose and be pumped into the lungs, where they can cause an embolism. A fat embolism develops in a similar way to a “normal” embolism, except that instead of a blood clot, a droplet of fat is responsible for closing a blood vessel.

Such a fat droplet can come from the inside of a bone, for example. Especially in the case of a broken bone, many such fat droplets enter the bloodstream. Some of them can be pumped into the lungs and block the blood vessels there.

Further complications of such a fat embolism arise when the droplets become entangled in the vascular system of another organ. There, too, the disturbed blood flow can cause severe damage to the organ. Taking the pill can promote pulmonary embolism if other factors are added.

Its use as the sole cause of pulmonary embolism or thrombosis (a blood clot in a vein) is relatively unlikely. However, in recent years thrombosis has been more common when taking minipills containing a progestin (a sex hormone) as the sole active ingredient. For this reason, special attention should be drawn to the increased risk of thrombosis or another preparation should be prescribed if other risk factors for thrombosis are known.

If other risk factors for thrombosis are added to the pill, such as smoking, a known blood clotting disorder or prolonged immobility due to travel or surgery, this can be the cause of a pulmonary embolism. Together with smoking, alcohol is one of the known risk factors that can cause pulmonary embolism. This is due on the one hand to the fact that the alcohol in the blood causes the so-called INR to rise.

This value describes how fast the blood coagulates and if the value increases, this means that the blood clotting is faster. This mainly affects people who drink alcohol regularly. If the consumption is stopped, the value returns to normal.

Another reason why alcohol promotes pulmonary embolism is that alcohol is broken down in the liver. This can limit the effect of blood thinners, which also work in the liver. This concerns, for example, the drug Marcumar ®, which many patients have to take because of a previous thrombosis or cardiac arrhythmia.

Alcohol also leads to increased urine production in the kidney and more frequent urination. This increased loss of fluid leads to a thickening of the blood, which can lead to thrombosis or pulmonary embolism. Various reasons can lead to pulmonary embolism when using drugs.

The use of stimulant drugs such as cocaine or ecstasy leads to an increase in heart rate and blood pressure.This can cause a thrombus, i.e. a blood clot that is already present, to break away from the wall of the vein and be flushed into the pulmonary circulation, where it moves a pulmonary artery. Furthermore, the use of these drugs causes heavy sweating and, in combination with the often insufficient amount of drinking, the blood thickens and thrombosis can occur more easily. Another mechanism of action of the drugs is a narrowing of the blood vessels, which can promote a heart attack and can be life-threatening with an existing thrombosis.

If a drug is injected through a vein, this always means an irritation of the vein, on the one hand by the chemical ingredients of the drug, on the other hand by piercing it with a needle. If this vein is used frequently, chronic phlebitis can occur, which can lead to a venous blood clot in the affected vessel. This blood clot can be the cause of a pulmonary embolism when it enters the lung via the bloodstream.

During pregnancy, women are particularly susceptible to pulmonary embolism. Due to the many hormonal changes that occur in the body, the clotting system is also affected. In order to protect against too much blood loss during childbirth, the blood is made slightly easier to clot.

In addition, the blood from the veins flows back to the heart much more slowly. Both changes favour the development of thromboses (blood clots) in the veins. The clots can detach from the vein and be transported with the bloodstream to the heart. From there they are pumped directly into the lungs, clogging the vessels and causing an embolism.