Pulmonary embolism

Pulmonary embolism

Pulmonary embolism is the sudden blocking of an artery of the lung, also known as pulmonary artery, by a embolus – a blood clot or a thrombus.

  • The functions of the arteries of the lungs are to carry enough blood containing oxygen and nutrients to keep the lung tissue healthy and to carry carbon dioxide to the lungs for removal from the body.
  • But, when a large artery to the lung is blocked by an embolus, the amount of blood supplied may be insufficient, eventually causing lung tissue to die.
  • About 10% of people suffering from pulmonary embolism suffer some lung tissue death, which is also called pulmonary infarction.
  • Sometimes the body breaks the small clots quickly, keeping damage to a minimum.
  • Large clots take much longer to disintegrate, so more damage is done.
  • Large clots may cause sudden death by blocking so much of the lung arteries that the oxygen supply to the body is inadequate to sustain life or by placing an excessive strain on the heart.
  • The prevalence of pulmonary embolism in people admitted to the hospital is about 1%.
  • When an autopsy is performed, pulmonary embolism is often unexpectedly found to be the cause of death in about 5% of the people.

Causes

  • The most common type of embolus that travels to the lungs is a blood clot, usually, one that forms in a leg or a pelvic vein when blood flow slows down or stops, as may occur in leg veins when a person stays in one position for a long time.
  • People who have been on prolonged bed rest and those sitting for long periods without moving around (as may happen during air travel) are at particular risk.
  • When the person starts moving again, the clot can break loose.
  • Far less often, blood clots form in the veins of the arm or in the right side of the heart. Once a clot breaks free into the bloodstream; it usually travels to the lungs.
  • Another type of embolus may form from fat, which can escape into the blood from bone marrow when a bone is fractured.
  • An embolus may also form from the amniotic fluid being forced into the pelvic veins during childbirth.
  • However, both fat and amniotic emboli are rare. If they form, they usually lodge in small vessels like arterioles and capillaries of the lungs, where they generally cause less damage than the blood clots.
  • However, if many of these blood vessels are obstructed, acute respiratory distress syndrome or pulmonary hypertension may develop. Both of these conditions can lead to respiratory failure, heart failure and shock.
  • Cancerous tumor fragments can break into the circulation to form emboli, which, if they are numerous, can cause pulmonary hypertension as the cancer spreads throughout the lungs.
  • Air bubbles may form an emboli and cause pulmonary embolism after a vein has been exposed to large amounts of air, as may occur during intravenous infusion of drugs, nutrients or fluid.
  • Air emboli may also form when a vein is being operated on or when a person is being resuscitated.
  • An additional risk is when a person dives underwater and the risk depends upon how deep he dives and how fast he ascends to the surface of the water.

Symptoms

  • Symptoms depend upon the extent to which the pulmonary artery is blocked and on the person’s overall health.
  • For example, people who have other diseases such as chronic obstructive pulmonary disease or coronary artery disease, may have more disabling symptoms.
  • Small emboli may not cause any symptoms.
  • Most emboli cause shortness of breath which comes on very quickly.
  • Shortness of breath may be the only symptom especially if pulmonary infarction does not develop.
  • Often the breathing is very rapid and a person feels anxious or restless and appears to have an anxiety attack.
  • Larger emboli commonly cause sharp pain in the chest especially when the person inhales. This type of pain is called pleuritic chest pain.
  • In some people, the first symptoms of pulmonary embolism may be light headedness, fainting or seizures.
  • These symptoms usually result from a sudden decrease in the heart’s ability to deliver enough oxygen-rich blood to the brain and other organs.
  • People with obstruction of one or more large pulmonary arteries, have a blue skin colour and can die suddenly.
  • The symptoms of pulmonary embolism develop abruptly, whereas the symptom of pulmonary infarction develops over the following hours.
  • If pulmonary infarction occurs, the person experience soughing that may produce blood-stained sputum, sharp chest pain when the person breathes in and in some cases, fever.
  • Symptoms of infarction often last several days but usually become milder every day.
  • In people who have recurring episodes of pulmonary emboli, symptoms such as chronic shortness of breath, swelling of the ankles or legs, and weakness tend to develop progressively over weeks, months or years.

Diagnosis

  • A doctor suspects pulmonary embolism based on the person’s symptoms and predisposing factors, such as a recent surgery or a prolonged period of bed rest.
  • A large pulmonary embolism may be relatively easy for a doctor to diagnose, especially when there are obvious preconditions, such as signs of a blood clot in a leg.
  • Certain procedures are often needed to confirm the diagnosis.
  • Even with these procedures, however, many emboli can be quite subtle and difficult for doctors to diagnose conclusively.
  • A chest X-ray may reveal subtle changes in the blood vessel patterns after embolism and signs of pulmonary infarction.
    • However, the results are often normal and even when they are abnormal; they rarely enable the doctor to establish the diagnosis with certainty.
  • An electrocardiogram may show abnormalities, but often these abnormalities are transient and can only support the possibility of a pulmonary embolism.
  • A lung perfusion scan is one of the best tests for diagnosing pulmonary embolism.
    • In this test, a tiny amount of radioactive substance is injected into a vein and travels to the lungs, where it outlines the blood supply of the lungs.
    • Areas without normal blood supply appear dark on the scan because no radioactive particles can reach them.
    • Normal scan results indicate that a person does not have significant blood vessel obstruction.
    • Abnormal scan results support the possibility of pulmonary embolism but may also reflect conditions other than pulmonary embolism, such as obstructive lung disease.
  • A lung ventilation scan is usually coupled with perfusion scan.
    • The person inhales a harmless gas containing a trace amount of radioactive material which is distributed throughout the small air sacs of the lungs.
    • The areas where carbon dioxide is being released and oxygen taken up can then be seen on a scanner.
    • By comparing this scan to the pattern of blood supply shown on the perfusion scan, a doctor can usually determine whether a person has had a pulmonary embolism by a mismatch between ventilation and blood perfusion.
  • Pulmonary angiography is an accurate means of diagnosing pulmonary embolism, but it poses some risks and is more uncomfortable than the other tests.
    • It is only performed only when other tests fail to demonstrate a conclusive diagnosis of pulmonary embolism.
  • In an X-ray procedure, a radiopaque dye is injected into the pulmonary arteries.
    • A pulmonary embolism shows up as blockage in an artery.
  • A certain type of computed tomography (CT) called CT angiography is another accurate test.
    • CT angiography can be used if pulmonary angiography is not available or if the person should not undergo this test for some reason.
  • Additional tests such as an ultrasound to examine the legs for blood clots in the veins may be performed to find out where the embolus originally developed.
  • A blood test (D dimer test) can provide additional support of the diagnosis.
  • A normal test result can help to exclude pulmonary embolism as the cause of a person’s symptoms.

Prevention

  • Given the dangers of pulmonary embolism and limitations of treatment, doctors try to prevent blood clots from forming in the veins of people at risk of pulmonary embolism.
  • In general, a person who is prone to clotting should try to be active and move around as much as possible.
    • For example, when traveling on an airplane for a long period, the person should try to get up and move around every two hours.
  • For people who have undergone surgery, especially the older people, the risk of clot formation can be reduced by the following measures :
    • Wearing compression elastic stockings
    • Doing leg exercises
    • Getting out of bed and becoming active as soon as possible.
  • For people who cannot move their legs, intermittent air compression devices can provide rhythmic external pressure to keep the blood moving in legs and thighs.
  • However, these devices alone are inadequate to prevent clot formation in people who have undergone hip or knee surgery.
  • Anticoagulant drugs are given.
    • Heparin is the most widely used therapy for reducing the likelihood of clots formation in calf veins after any type of major surgery, especially surgery for the legs.
    • Hospitalized people at high risk of developing pulmonary embolism, benefit from small doses of heparin even if they are not undergoing surgery.
    • Small doses are injected just under the skin shortly before the operation and ideally until the person is up and walking again.
    • Low dose heparin does not increase the frequency of major bleeding complications, but heparin can increase minor oozing of blood from wounds.
    • Low-dose heparin can also be used for operations involving the spine or brain.
    • A different form of heparin called low molecular weight heparin, is equally or even more effective in preventing clots than the use of traditional heparin.
    • Low molecular weight heparin is also injected just under the skin and is usually continued until the risk of developing clots has passed.
    • Warfarin is given when a person has undergone certain types of surgery that are particularly likely to result in clots, such as surgery for a hip fracture or a joint replacement.
    • Warfarin therapy may need to be continued for weeks or months.
    • Low molecular weight heparin is also effective for people in this situation.

Treatment

  • Treatment of pulmonary embolism begins with the administration of oxygen and if necessary, analgesics are given to relieve pain.
  • Anti-coagulant drugs such as heparin are given to prevent the existing blood clots from enlarging and additional clots from forming.
  • Heparin is given intravenously to achieve a rapid effect, and doctors carefully regulate the dose.
  • Doctors strive to achieve a full effect within the first 24 hours of treatment.
    • Otherwise, the person is at high risk of more pulmonary emboli and new clots or enlargement of existing clots in leg and pelvic veins.
  • Low molecular weight heparin is probably equally effective to traditional heparin and does not require the blood test monitoring that conventional heparin requires.
  • Warfarin is given next. It inhibits clotting but it takes longer to start working. In other words, it has delayed onset of action.
    • Also, since warfarin is taken by mouth, it can be used long-term.
  • Heparin and warfarin are given together for 5 to 7 days, until blood tests show that warfarin is effectively preventing clotting. Then, heparin is discontinued.
  • The duration for which anti-coagulants are given to a person depends upon the person’s situation.
  • If pulmonary embolism is caused by temporary predisposing factor, such as surgery, treatment is given for 2 to 3 months.
  • If the cause is some long-term problem, such as prolonged bed rest, treatment is given for 3 to 6 months. In certain cases, treatment must continue indefinitely.
    • For example, people who have recurrent pulmonary embolism, often due to a hereditary predisposition to clotting, usually take anticoagulants indefinitely.
    • While taking warfarin, the person periodically has to have a blood test to determine if the dose needs to be adjusted. Changes in diet and many other drugs may affect the magnitude of anticoagulation by this drug.
    • If excessive anticoagulation occurs, severe bleeding in a number of body organs can develop.
  • Thrombolytic therapy appears to be in danger of dying of pulmonary embolism.
  • Thrombolytic drugs such as streptokinase or tissue plasminogen activator break up and dissolve the clot.
  • However, these drugs cannot be given to people who have had surgery in the preceding 2 weeks, are pregnant and have had a recent stroke or tend to bleed excessively.
  • Surgery may be needed to save someone with severe embolism.
    • Removal of the embolus from the pulmonary artery may be lifesaving.
  • Surgery is also used to remove long standing pulmonary clots in the artery that cause persistent shortness of breath and pulmonary hypertension.
  • A filter can be surgically placed in the main vein in the abdomen that drains blood from the legs and pelvis to the right side of the heart.
    • Such a filter can be used if emboli recur despite anticoagulant treatment or if anticoagulants cannot be used or cause significant bleeding.
    • Because clots generally originate in the legs and pelvis, this filter usually prevents them from being carried into the pulmonary artery.
  • For emboli that form from fat or amniotic fluid, oxygen therapy and use of ventilator may be needed.
  • In addition, emboli that develop from amniotic fluid may stimulate the formation of blood clots; agents such as cryoprecipitate are sometimes needed to block certain key steps in the formation of these clots.
    • For example, blocking the formation of fibrin deposits in the circulation.

Prognosis

  • About half of the people with untreated pulmonary embolism will have another embolism.
  • As many as half of these recurrences may be fatal.
  • Treatment with anticoagulant drugs can reduce the rate of recurrence to about 1 in 20 people.
    • Only about 1 in 5 of these people will die of pulmonary embolism.
  • The likelihood of dying depends upon:
    • The size of the embolus
    • Size of the pulmonary artery that is blocked
    • Number of the pulmonary arteries blocked
    • Person’s overall health status
  • Anyone with a serious heart or lung problem is at a greater risk of dying from pulmonary embolism.
  • A person with normal heart and lung function usually survives unless the embolus blocks half or more of the pulmonary vessels.
  • If death occurs from pulmonary embolism, it occurs rapidly often within 1 to 2 hours.
  • An air embolism can cause death, but only if the amount of air that reaches the heart and pulmonary arteries is large.
  • Death occurs with a large air embolus not only because blood flow to much of the lungs is blocked, but also because heart cannot effectively pump blood.

Factors which predisposes a person to blood clots

  • Advanced age
  • Heart attack
  • Blood clotting disorder
  • Cancer
  • Heart failure
  • Major surgery
  • Irregular heartbeat or atrial fibrillation
  • Obesity
  • Prior blood clot
  • Paralysis
  • Pelvis, hip or leg fracture
  • Stroke
  • Prolonged bed rest or inactivity
  • Use of oral contraceptives (especially after 35 or in someone who smokes)

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By |2018-08-07T02:55:51+00:00August 6th, 2018|Disease/pathological condition|0 Comments

About the Author:

B. Pharm (K.L.E. society's S.V.V. Patil College of Pharmacy, Bengaluru) M. Pharm (Maharishi Arvind Institute of Pharmacy, Jaipur)

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