Pulmonary embolism or also known as venous thromboembolism (VTE), or lung blood clot, or tumor embolus is a sudden blockage in one of the pulmonary arteries in the lungs by a blood clot. The common cause of pulmonary embolism is deep vein thrombosis where the blood clot is formed in the deep veins of the legs to then pass through the blood stream until it reaches the lung.

A patient with pulmonary embolism may show many symptoms such as shortness of breath, chest or upper part of the back pain, coughing, dizziness, fainting, and irregular heartbeat. Symptoms associated with deep vein thrombosis include swelling, tenderness, and change in the skin color of the affected leg.

Many factors increase the risk of pulmonary embolism such as age, prolonged immobility, smoking, obesity, estrogen supplement, and pregnancy in addition to the patient’s medical and family history. 

It is difficult to diagnose pulmonary embolism, especially with pre-existing heart or lung diseases. Pulmonary embolism is diagnosed based on the medical history, physical exam, and diagnostic tests. Diagnostic tests conducted for pulmonary embolism symptoms include blood tests, chest x-ray, ultrasound, spiral CT scan, and chest magnetic resonance imaging,

 Pulmonary embolism is a critical condition that must be treated as soon as it appears. The available treatments for pulmonary embolism include medications and surgery. Anticoagulants drugs such as heparin and warfarin, are used. In some cases, certain such as clot removal and vein filter may be conducted. Certain precautions should be taken into consideration when prescribing treatment for pregnant women and cancer patients.  

To prevent pulmonary embolism from occurring, individuals should be physically active and avoid setting for long period of time even in post-surgery. Pulmonary hypertension and weakness in the heart muscle, in addition to hypertension within vessels in the right side of the heart may be considered pulmonary embolism complications.

According to a study in a Canadian journal, Experimental and clinical cardiology, the incidence of pulmonary embolus is estimated to be around 60 to 70 per 100,000 in general population.

Pulmonary embolism 6 is the presence of a blood clot in one of the pulmonary arteries of the lungs, causing a sudden blockage of these arteries.

Blood clots can form for different reasons. Commonly, pulmonary embolism is caused by deep vein thrombosis (DVT), a condition by which blood clots form in deep veins of the legs. The formed blood clot moves within the bloodstream to the lungs, causing an artery to be blocked. This blockage causes pulmonary infarction, where portions of the lung die because they do not receive any blood. This condition makes the lungs unable to deliver oxygen to the remaining parts of the body.

When blood flow is restricted or slowed down within the deep veins of the legs, it can cause formation of blood clots. This can occur when individuals sit, or do not move their legs for a long time, such as:

• Certain post-surgery cases.
• Traveling for a long time in a car or airplane.
• Persons who are obligated to remain in bed for a long time due to certain health conditions.

Rare cases of pulmonary embolism can be caused by other things blocking block the blood vessels, such as part of a tumor, or other tissue, and air bubbles.

Several risk factors can make a person more likely to develop pulmonary embolism such as:

• Family history

The risk of having pulmonary embolism is increased if the person has a family member suffering from venous blood clots or pulmonary embolism, as a result of inherited disorders that affect blood, making it more likely to clot.

• Medical history

The risk of pulmonary embolism is elevated in individuals who have certain medical conditions or take some types of medications, such as:

• Heart disease

Heart disease increase the chance of blood clot formation, especially heart failure.

• Cancer

The chance of pulmonary embolism is increased as a result of certain types of cancers such as pancreatic, ovarian and lung cancers. Furthermore, many cancers with metastasis, due to the high levels of the material that helps blood coagulate, in addition to chemotherapy can also increase the chance of blood clotting.

• Surgery

After surgery, chances are increased for blood clots in veins that are damaged from surgery or injured in other ways.

• Age

The risk of pulmonary embolism increases with age. The risk is doubled for every 10 years after age 60. (10)

• Prolonged immobility

The risk of blood clots increases during sitting and immobility for long periods, especially in people who have undergone operations that require long-term rest or when making trips for long periods.

• Smoking

Tobacco use, especially if accompanied by other risk factors, increases the risk of pulmonary embolism.

• Obesity

As the body weight increases, the risk of pulmonary embolism increases, especially in women with high blood pressure or those who smoke.  

• Estrogen supplement

Clotting factors in the blood are increased by estrogen in birth control pills and in hormone replacement therapy, particularly with those smokers or overweight.

• Pregnancy

Pregnant women have their fetuses inducing pressure on veins of the pelvic area, which leads to a decreased flow speed of blood in the leg area.

There are four factors on which the pathophysiology of the pulmonary embolism depends:

• The size of the emboli; a piece of thrombus circulating the bloodstream to be stuck in a vessel, and the extent of occlusion of the vascular tree.
• Past case of cardiopulmonary condition in the patient.
• Chemical vasoconstriction which is the narrowing of the blood vessels, because platelets that adhere to the embolus release serotonin; a neurotransmitter found in the brain, bowels and blood platelets, and thromboxane which is responsible for blood clotting and constriction of blood vessels, in addition to fibro peptide B, which is a product of the breakdown of fibrinogen responsible for blood clotting.
• The reflex vasoconstriction that has a possibility to occur as a result of pulmonary artery dilatation.

The pathophysiology of pulmonary embolism:

• Haemodynamic changes

Right heart overload is the result of high pulmonary resistance caused by vessel obstruction and response vasoconstriction. When vessel obstruction is profound, forward flow to the left heart is decreased, causing heart failure and shock.

• V-Q mismatch

Large emboli get stuck in the central vessels, leading to hemodynamic consequences. Small emboli clears peripheral vessels and irritates the pleural. Parts of the lung ,located distal to the emboli, lack perfusion. Vascular compromise known as atelectasis, which involves partial or complete lung collapse  and bronchoconstriction lead to perfusion to most but not all parts. Increased minute ventilation compensates for the resulted arterial hypoxemia which is low oxygenated arteries. The process of compensation mostly ends up in releasing more CO2 than necessary which is known as hypocapnia.

Signs and symptoms of Pulmonary Embolism

Many symptoms of a pulmonary embolism may appear such as:

• Shortness of breath that is sudden and unexplained.
•  Sharp or stabbing chest or upper part of the back pain.
• Coughing that could be accompanied by blood.
• Dizziness.
• Fainting.
• Irregular heartbeat.
• Too much sweating.
• Fever.
• Clammy or discolored skin.

Signs related to deep vein thrombosis include:

• Swelling of the legs or swelling of the vein along the leg.
• Leg pain or tenderness.
• Swollen or tender leg becomes warmer.
• The affected leg becomes red or with discolored skin. 

Diagnosing pulmonary embolism is difficult, particularly in individuals who have underlying lung or heart condition.  Diagnoses depends on the medical history of the person, physical exam, and the result of the diagnostic tests.

• Medical History

The doctor will collect information about the person to understand more about the person medical case:

• The presence for deep vein thrombosis or not.
• Estimating the risk of having pulmonary embolism.
• Exclude other possible causes for the symptoms.

• Physical Exam

Physical exam is also conducted to examine the legs for signs of DVT, in addition to checking blood pressure, heart and lungs.

• Diagnostic Tests

Various tests can be done to diagnose PE depending on the case severity, risk factors, testing options provided and other pre-existing conditions. Such tests include:

• Blood tests

D-dimer, a clot-dissolving substance, is one of these tests. This test indicates the presence of a substance that result from a blood clot break up. Usually, patients with pulmonary embolism have a high level of D-dime.  Normal levels of this substance, without any present risk factors could exclude PE from the diagnosis.

In addition to other blood tests check for inherited disorders that cause blood clots.

Blood tests are used to measure the amount of oxygen and carbon dioxide in the blood. Low levels of oxygen in the blood could point out the presence of a blood clot in the blood vessels.

Chest X-ray

X-ray provides images of the heart, lungs, large arteries, ribs, and diaphragm. This test aids in excluding other conditions with similar manifestation.

• Ultrasound

This test is used to look for the presence of blood clot inside the leg’s vein by detecting blood flow of the veins via sound waves.

• Spiral CT scan

This test provides precise three dimensional (3-D) images of the body. It can detect any abnormalities within the lung’s arteries. Contrast material is sometimes used to outline pulmonary arteries.

• Pulmonary angiogram

This test is the most accurate test in detecting pulmonary embolism, but it is performed only when other tests fail to provide a conclusive diagnosis. It requires a high degree of skill to administer and has potentially serious risks. Pulmonary angiogram test creates an image for blood flow in the lung’s arteries.  

• Chest magnetic resonance imaging (MRI)

MRI are used to create an image of the body's internal structures. This test tend to be costly, so it is used in certain cases to avoid radiation to the fetus in pregnant women and people with harmed kidneys from dyes used in other tests.

• Echocardiography (echo)

It is used to create a moving image of the heart via sound waves. This test is needed to check for the heart’s function and for identifying blood clots inside the heart.

• Electrocardiogram (EKG)

This simple, painless test is used to detect and record the heart's electrical activity.

Treatment focuses on preventing an existing clot from becoming bigger, stopping the formation of new clots, and removing or breaking up the clot. Pulmonary embolism needs immediate treatment. These treatments include the following:

• Medications

• Anticoagulants

These blood thinners change blood chemicals to stop easy clot formation, in addition to new clot formation while the body is breaking up the blood clots already formed.

• Heparin

It is the initial drug used to treat pulmonary embolism, because it has a instant effect. It should be used for at least five days as an injection trough the vein or under the skin.

• Warfarin

After the initial heparin injections, warfarin should be taken. Usually, warfarin is prescribed for longer periods of time that could be for three months or more or even a lifetime.

A person on warfarin should be monitored in their diet, alcohol consumption, exact time for medication every day, avoiding other un-recommended medication or herbal medicines and have regular blood tests to confirm taking the correct doses.

• Dabigatran

This drug targets the protein that helps to form blood clots, which is called thrombin. It is also used to prevent and treat deep vein thrombosis. According to patient’s age and medications taken for other health conditions, the dabigatran dose is determined.

• Rivaroxaban

Deep vein thrombosis and pulmonary embolism are prevented and treated with this drug.

Bleeding risk and other clinical criteria determines the length of treatment. The dose depends on the case where the patient could be treated for the first time or for recurrent pulmonary embolism.

• Apixaban

This oral drug is also used to prevent and treat deep vein thrombosis and pulmonary embolism. It is taken for the first seven days twice a day. The dosage is then halved and taken twice a day for at least three months.

• Novel oral anticoagulants (NOACs)

It is a new anticoagulants used to treat pulmonary embolism and other thromboembolism diseases. These medications have a rapid effect with less drug-drug interaction.

• Thrombolytics (clot dissolvers)

These medications are used only in life-threatening situations since they cause sudden and severe bleeding. They usually accelerate the breakdown of the blood clot.

It is worth mentioning that pregnant women and people with cancer should have special considerations. Warfarin tablets should not be used for both; instead heparin injections should be used. In cancer patients, treatment should last six months or until cured.

• Other procedures

• Clot removal

If the blood clot in the lung is threatening the patient's life, the doctor will use a catheter which is a thin, flexible tube to remove it.

• Vein filter

This technique is used when anticoagulants cannot be used or when they are not effective or fast enough. The doctor uses a catheter to place a filter in the body’s main vein called the inferior vena cava, where it is guided from the patient's legs until it reaches the right side of the heart. This filter forms a barrier for the clot so it will not pass until the lung

There are two major complications related to pulmonary embolism are as follows:

• Pulmonary hypertension can be caused by pulmonary embolism. This condition represents an elevation in the lung’s pressure. Rarely, chronic pulmonary hypertension, also known as chronic thromboembolic pulmonary hypertension occurs as a result of frequently developing small emboli over time.

• Weakness in the heart muscle is caused by obstructions in the arteries that leads to elevated blood pressure within the vessels in the right side of the heart.

To prevent pulmonary embolism, deep vein thrombosis should first be prevented by following these methods:

• People undergoing surgery should take anticoagulants, as well as patients admitted to hospital for a heart attack stroke or complications of cancer.
• Wear compression socks that help move the blood in the veins and leg muscles more effectively.
• Elevation of the feet is useful in reducing the risk of blood clotting.  Books or blocks can be placed to raise the bottom of the bed to ensure that the feet remain raised all night.
• A patient who has undergone surgery is advised to move as much as possible, even if he has some pain, to avoid a pulmonary embolism.
• Pneumatic compression can be used by wearing it on the leg area exactly in the thigh-high or calf-high, where it is inflated and deflated automatically and frequently to massage the legs in order to improve blood circulation in this area.
• When traveling for long periods, it is recommended to take a break every period to move the blood inside the body and avoid the occurrence of blood clots.
• The risk of pulmonary embolism can also be reduced by stopping smoking, exercising on a daily basis and consuming a healthy balanced diet.

Prognosis of Pulmonary Embolism

It is difficult to predict the extent of a patient’s recovery from pulmonary embolus. Usually, it depends on:

• The original cause of the pulmonary embolus like cancer, major surgery, or an injury.
• Blood clot size in the lung.
• Whether blood clots dissolve or not with time.

Some cases may have long-term heart and lung problems and in severe cases, the disease can lead to death.

According to a study published in a Canadian journal, Experimental and clinical cardiology, the incidence of pulmonary embolus is estimated to be around 60 to 70 per 100,000 of the general population. The European guidelines for the diagnosis and management of pulmonary embolus states annual incidence rates of pulmonary embolus of around 0.5 to 1.0 per 1000 populations.