An embolism occurs when foreign material, such as a blood clot or air bubble, travels through the bloodstream and becomes lodged in a blood vessel, blocking the flow of blood. Embolisms can occur in veins, which carry oxygen-poor blood back to the heart and lungs, as well as arteries, which carry oxygen-rich blood from the heart to the tissues of the body. Depending on the size of the embolism and which blood vessel it is obstructing, the result can range from a complete lack of symptoms to a life-threatening emergency.

Embolisms are usually described by either the type of material that is involved, such as air or fat, or the vessel that is obstructed, such as the pulmonary artery. The most common type is a thromboembolism, which is caused by a piece of a blood clot. This could lead to heart attack or stroke.

The tests used to diagnose an embolism depend on which type of embolism is suspected. Similarly, treatment will depend on which type of embolism is diagnosed. Treatment could include medications to dissolve the embolism or increase blood flow, surgery to remove the embolism or methods to prevent or treat risk factors for further emboli.

An embolism occurs when foreign material travels through the bloodstream and becomes lodged in a blood vessel. Embolisms typically become lodged in the large or medium-sized arteries located anywhere in the body, especially in the neck, lungs, brain, intestine, legs, arms or kidneys.

The particle causing the blockage (called an embolus) could be one of many substances that may travel through the bloodstream, including:

An embolus travels through the branches of an artery or vein until it becomes stuck. Once lodged, it obstructs oxygen-rich blood from nourishing whatever parts of the body lie beyond it. As a result, the tissues on the other side of the blockage begin to die from lack of oxygen. If oxygen depletion continues long enough – sometimes only a matter of minutes – oxygen–starved tissues and organs will stop functioning and become permanently damaged.  

Embolisms are typically named after the blood vessels they are lodged in or the composition of the embolus itself (e.g., a blood clot). Some of the more common embolisms include:

• Cerebral embolism (intracranial embolism). One of the most common causes of a stroke. It occurs when an embolus (usually a blood clot) becomes lodged in an artery in the brain, blocking oxygen-rich blood from nourishing the portion of the brain beyond the blocked artery. Without adequate oxygen, that area of the brain suffers tissue damage or death, causing typical stroke symptoms such as speech impairment, one-sided paralysis, or problems with comprehension or vision (depending on which portion of the brain was damaged).
  
  
• Arterial embolism. Most commonly seen as a complication of heart disease. Atrial fibrillation may also be present. Frequently, there is more than one embolus. Recurrences are common even after successful treatment of previous embolisms. Arterial embolisms tend to become lodged at the fork of major arteries, with over 50 percent affecting blood vessels in the lower extremities.
  
  
• Venous embolism. Much less common than arterial embolisms. Venous embolisms can be caused by globules of fat or bone marrow. These globules usually occur after a bone fracture and are released from the fracture site of a long bone (such as an arm or leg bone). In rare cases, a venous embolism may be caused by a bubble of air that has entered the body through a central intravenous line (IV) or during certain brain operations such as a sitting craniotomy.
  
  
• Pulmonary embolism. An embolism (usually a blood clot from the pelvic veins or deep veins of the leg, a condition called deep vein thrombosis) that becomes lodged in the pulmonary artery in the chest. This blockage causes a true medical emergency because it obstructs the blood supply to the lungs. It is a commonly occurring embolism that affects approximately 600,000 Americans every year, and 10 percent of those embolisms result in death.
  
  
• Amniotic fluid embolism. A very rare, life-threatening embolism that can occur in late pregnancy. Amniotic fluid enters the uterine veins through a tear in the placental membranes and travels to the lungs, sometimes leading to sudden cardiac death.
  
  
• Leg or arm embolism. An embolism, usually a blood clot, which blocks one of the arteries that supplies blood to an arm or leg.
  
  
• Fat embolism. An embolism that may occur after a long bone has fractured, releasing fat or bone marrow globules from the fracture site into the bloodstream. The globules then travel to the lungs and become trapped in the pulmonary capillaries, resulting in the same life-threatening situation as a pulmonary embolism.
  
  
• Air embolism. Bubble(s) of air or other gases that enter the circulation and travel to the lungs, heart or brain. There, they block normal blood flow and cause life-threatening medical emergencies. Air embolisms are a leading cause of death in scuba diving accidents (a condition called “the bends”) and can also occur during surgeries involving the head and neck, as well as vaginal delivery or cesarean sections (“C-section”).
  
  
• Paradoxical embolism. The result of an embolus that has traveled from the veins to the arteries to the brain (where it blocks a cerebral artery), or any other systemic artery. The embolism is “paradoxical” (contrary to the usual) because normally blood cannot travel from a vein into an artery. The condition can occur when an embolus crosses from the right side of the heart to the left side through a hole in the septum (the muscular wall that separates the left and right sides of the heart). The hole is usually the result of an unrepaired congenital heart defect (e.g., patent foramen ovale, atrial septal defect, ventricular septal defect).
  
  
• Cholesterol embolism. A life-threatening complication that can arise spontaneously or from medical treatments designed to reduce or dissolve plaque in the arteries, such as balloon angioplasty. During these medical treatments, cholesterol crystals may be released from the plaque into the bloodstream. If the cholesterol crystals travel to the lower part of the body, they can obstruct a blood vessel and cause a cholesterol embolism. Such embolisms usually obstruct small arteries. Besides balloon angioplasty, cholesterol crystals can be released from plaque through the use of anticoagulants, other catheter-based procedures and a type of thrombolytic therapy that uses t-PA (tissue plasminogen activator).
  
  
• Therapeutic embolism (embolization). The deliberate creation of an embolus to obstruct a blood vessel in order to stop internal bleeding or to cut off the blood supply to a tumor. These man-made emboli can be made of many different materials, such as fibrin, metal coils, silicone balloons, wool or medicinal glue.
  

Several conditions and common risks make people more susceptible to blood clots, thereby increasing the risk for embolism. They include:

• Blood abnormalities, which may be congenital (e.g., developed before birth) or acquired (e.g., from disease or medication).
  
  
• HIV, particularly in persons younger than 50 years of age who have respiratory symptoms.
  
  
• Trauma to the legs, which may be caused by an accident, surgery or conditions such as deep vein thrombosis.
  
  
• Menopausal women using hormone replacement therapy, especially a combination of estrogen and progestin, are more likely to develop deep vein thrombosis, which can lead to pulmonary embolism.
  
  
• Advanced age, especially over 70.
  
  
• Obesity (body mass index greater than 30).
  
  
• Cancer. Some types of cancer are associated with blood clot formation and emboli.
  
  
• Infection. Recent studies have shown some evidence that infection (e.g., urinary tract infection, respiratory infection) can increase the risk of blood clot formation, particularly deep vein thrombosis.
  
  
• Pregnancy.

Other risk factors may include taking certain medications such as birth control pills and medications for osteoporosis.

SCUBA divers are particularly at risk for air or gas embolisms that can occur if the diver resurfaces too quickly. In this scenario, pressure builds inside the lungs, causing them to rupture and release air or gas into the bloodstream.

The symptoms of an embolism are determined by several factors, the most important of which are the blood vessel involved and the size of the embolism. If the embolism is small and in a minor blood vessel, there may be no immediate symptoms at all, whereas a large embolus can totally obstruct blood flow to a vital area and may be life threatening. For example, if a thromboembolism is large enough to totally obstruct an artery, then the tissue supplied by the artery will die. If this occurs in one of the coronary arteries on the surface of the heart, the patient will have a heart attack (myocardial infarction).

A cerebral embolism or, more rarely, a paradoxical embolism could lead to either a transient ischemic attack (TIA) or a stroke, both of which can produce symptoms that are temporary or permanent. The symptoms of a TIA or stroke include the following:

People may also have a variety of visual problems that include the following:

• Partial loss of vision or complete blindness
• Double vision
• Abnormal eye movements
• Blurred vision
• A gray shading or fogging within the field of vision

The signs and symptoms of an arterial embolism depend on the artery that is blocked and the organs or region that it had been supplying. Obstruction of an artery in an extremity usually results in symptoms in that extremity, which include the following:

• Pain
• Numbness
• Coldness
• Tingling
• Lack of pulse in the arteries on the far side of the blockage
• Paleness or mottling (splotches) on the skin
• A heightened sensitivity of the skin (paresthesia)
• Muscular spasm or paralysis

Later, blebs (blisters) and skin necrosis (tissue death) may appear, and gangrene may result.

The symptoms of venous embolism range from local pain, swelling and tenderness to sudden cardiac death.

The greatest risk factor for pulmonary embolism is the presence of deep vein thrombosis, or clots in the veins of the legs and pelvis. These clots may break off, travel through the circulatory system to the lungs, and become lodged, creating a pulmonary embolism. A pulmonary embolism produces symptoms such as the following:

• Chest pain
• Rapid heart beat (tachycardia)
• Feeling faint (dizziness)
• Shortness of breath (dyspnea)
• Rapid breathing
• Cough, sometimes with blood (hemoptysis)
• Rales or crackles (a lung sound heard when listening to the chest)

The symptoms of an amniotic fluid embolism include the following:

• Shortness of breath (dyspnea)
• Dramatic fall in blood pressure
• Rapid progression to cardiac arrest (in which the heart stops beating)

If a leg or arm embolism is not treated promptly, there is a danger that tissues on the far side of the blockage will die and gangrene may develop.

In cases of a fat embolism, which usually occurs approximately 48 hours after a major bone fracture, symptoms include the following:

• Tachycardia
• Rapid breathing
• Restlessness
• Confusion
• Rash
• Sleepiness
• Bluish tint to the skin (cyanosis)

An air embolism is a life-threatening emergency that will lead to the heart’s stopping (cardiac arrest) and sudden cardiac death if not treated immediately. A major cause of air embolisms are rapid ascents during deep-water dives. Symptoms usually appear very quickly after the ascent and may include:

• Dizziness
• Bloody froth from nose or mouth
• Paralysis
• Convulsions

One of the most common symptoms of a cholesterol embolism is blue toe syndrome. This condition is characterized by a bluish tint to the skin (cyanosis) caused by blockage of small blood vessels in the foot by cholesterol crystals.

Diagnosis of an embolism can be difficult and relies greatly on the patient’s recent medical history, keen observation of the patient’s current symptoms and the type of embolism that is suspected.

Deep vein thrombosis is the leading cause of a pulmonary embolism, one of the most dangerous types of embolus. When a pulmonary embolism is suspected in someone with a history of deep vein thrombosis, tests may include the following:

A cerebral embolism is one of the most common causes of stroke. When it is suspected, a CT scan is performed to determine whether the symptoms are due to a blockage of a cerebral artery or bleeding from a cerebral blood vessel or due to some other brain disorder. The results of the CT scan largely determine the treatment that will be given. The possibility of a paradoxical embolism must also be considered. To further determine the cause and extent of damage following an embolism, other tests may include:

• Electroencephalogram (EEG)
• Cardiac catheterization
• Magnetic resonance imaging (MRI)
• Blood tests
• Transesophageal echocardiogram

Diagnostic tests used to study other types of embolisms vary with the nature and size of the embolism and the part of the body affected. These tests include the following:

• Arterial blood gas study.
  
  
• Chest x-ray.
  
  
• Electrocardiogram (EKG).
  
  
• Angiogram. Considered the “gold standard” for imaging many suspected embolisms despite its inherent risks. The test consists of the injection of a radiopaque dye into a blood vessel in order to visualize a blockage or embolism with various x-ray imaging devices.
  
  
• Doppler ultrasound. The most sensitive noninvasive monitor, this is commonly used to detect and locate embolisms by using high–frequency sound waves to measure blood flow velocity and changes in blood density in blood vessels.
  
  
• Computed tomography scan (CT scan).
  
  
• Magnetic resonance imaging (MRI).

Treatment for an embolism depends on which type of embolism is present. Severe obstructions, such as those that occur with pulmonary embolism, can cause a person to collapse. Emergency hospital treatment is focused on keeping the patient breathing and maintaining circulation. The patient is typically treated for shock and given oxygen and anticoagulants. An embolectomy (surgery to remove the blockage) may be performed under general anesthesia. During an embolectomy, an incision is made into the affected artery, the embolus is sucked out by aspiration (suction). The incision is then closed with stitches (sutures) and/or surgical staples.

If the embolism is caused by a blood clot and surgery is not possible, or if the patient is stable and not in shock, then a thrombolytic drug (clot-buster) may be given along with an anticoagulant drug to prevent further clot formation. Clot-busting drugs are considered a vital part of treatment for strokes that are caused by blood clots. However, their use involves some risk of excessive bleeding and they may not be a suitable treatment method for all patients.

In the case of recurrent atrial emboli that are caused by atrial fibrillation, or an abnormal heart rhythm in the atria, physicians will usually prescribe an anticoagulant drug to be taken on a long-term basis.

Because pulmonary embolism is closely linked to deep vein thrombosis (DVT), physicians will try to prevent pulmonary embolism, by treating or preventing the DVT. Risk factors for DVT include cancer, obesity and heart failure. Those also at risk for DVT are elderly patients, people who have had surgery within the previous three months and those who have been immobile during the previous 30 days. DVT can be treated with blood-thinning drugs to prevent the formation of clots.

Patients with DVT who cannot tolerate anticoagulants may benefit from an infrequently used alternate treatment – a clot-trapping filter called a vena cava filter. The filter is inserted into the main vein leading from the legs to the heart and serves to stop large emboli from passing to the lungs. Researchers are working on developing a vena cava filter that can be removed after the threat of embolism has passed. There are some risks associated with permanent vena cava filters, including the potential for the filter to break down or fragment, dislodge, or even cause a blood clot themselves.

In treating a fat embolism, patients may be placed on a ventilator (e.g., a breathing machine). Aspirin or steroids may also be given to the patient in order to prevent further complications, such as DVT.

In the case of an air embolism, treatment consists of recompression in a hyperbaric chamber (a chamber that can increase atmospheric pressure) as soon as possible, oxygen administration and cautious rehydration.

Other embolisms are treated according to the size, nature and location of the obstruction. With severe embolisms, survival depends on the success of resuscitation attempts, the patient’s overall condition, the importance of the blood vessel being obstructed and the speed with which normal blood flow is reestablished. When the cause of the embolism can be diagnosed and treated early, the long-term outlook for the patient is good.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to an embolism:

1. Am I at increased risk for heart attack, stroke or pulmonary embolism?
   
   
2. If I've been diagnosed with existing blood clots, am I at risk for an embolism?
   
   
3. Why do you think I have an embolism?
   
   
4. What tests are you going to perform to diagnose the nature of my embolism?
   
   
5. How will you treat my embolism? Will I have to have surgery?
   
   
6. After you treat this embolism, will I be at an increased risk for another one?
   
   
7. What steps can I take to reduce my risk of an embolism?
   
   
8. Will anticoagulants interfere with my other medications?
   
   
9. Could this embolism be caused by a more serious health condition?
   
   
10. How soon will I be able to exercise or go back to work following treatment?