Pulmonary Embolism

A pulmonary embolism is a blood clot in the lung that travels from other areas of the body.

• A pulmonary embolism (PE) is a blood clot in the lung. The clot usually forms in smaller vessels in the leg, pelvis, arms, or heart, but occasionally the clot can be large.
• When a clot forms in the large veins of the legs or arms, it is referred to as a deep venous thrombosis (DVT).
• The pulmonary embolism occurs when part or all of the DVT breaks away and travels through the blood in the veins and lodges in the lungs.
• The clot travels through the vessels of the lung continuing to reach smaller vessels until it becomes wedged in a vessel that is too small to allow it to continue further. The clot blocks all or some of the blood from traveling to that section of the lung. These blockages result in areas in the lung were the disruption of blood flow does no allow the carbon dioxide waste to be delivered to the air sacs for removal (ventilation).
• Similarly, because blood is blocked to certain portions of the lung, oxygen can not be extracted from these same air sacs (perfusion). The process of matching the lungs ventilation with the blood flow through the lungs is disrupted, resulting in ventilation-perfusion inequalities. In other words, areas in the lung are ventilated (get air) but get no blood to exchange the waste product carbon dioxide with oxygen.
• If the pulmonary embolism is large, it may be capable of such a large mismatch, the patient cannot get enough oxygen into the blood and can be become acutely short of breath. In some instances, clots are so large that blood flow is blocked from the right side of the heart entering the lungs. This can result in instantaneous death.
• In other patients, the mismatch is not so profound, but still causes symptoms, especially when oxygen demand increases (for example, during exercise).
• Pulmonary infarction (death of lung tissue due to arterial blockage) is unusual because of collateral circulation.

Several risk factors can make a person more likely to develop a blood clot that can eventually break loose and travel to the lung. Virchow's triad explains the reasons why clots form. This triad includes 1) immobilization (which reduces flow), 2) damaged vessel wall (which forms a location for clot to start, and 3) Hypercoagulable state (which makes it easier for blood to clot.

• Immobilization: A stroke, broken bone, or spinal cord injury can result in confinement to bed so that clot formation can occur in either the arms or legs.
• Travel: Prolonged travel, such as sitting in an airplane or a long car trip, allows the blood to sit in the legs and increases the risk of clot formation.
• Recent surgery (includes hypercoagulable state due to surgical damage and the body trying to repair itself. It is also often associated with immobility and sometimes vessel damage depending on the surgery)
• Trauma or injury (especially to the legs)
• Obesity
• Heart disease (such as an irregular heartbeat)
• Burns
• Previous history of blood clot in the legs (DVTs) or pulmonary embolism

Conditions that increase clotting of the blood

• Pregnancy
• Cancer
• Estrogen therapy and oral contraceptives
• Certain protein and enzyme deficiencies

Not all pulmonary embolisms exhibit the same signs and symptoms. But certain symptoms may indicate that a pulmonary embolism has occurred.

The following signs and symptoms may occur (in the order they are typically seen):

• Chest pain: Pain is very sharp and stabbing in nature, has a sudden onset, and is worse when taking a deep breath (referred to as pleuritic chest pain).
• Shortness of breath, especially with exertion
• Anxiety or apprehension
• Cough: Usually, this cough is dry, but it may be associated with blood.
• Sweating
• Passing out

Doctors may suspect a blood clot if any of these symptoms occur in someone who has or recently had a swollen or painful arm or leg or who has any of the risk factors listed previously.

If a person experiences chest pain, call 911 or have someone take them to the nearest hospital's emergency department immediately.

Pulmonary embolism is difficult to diagnose from a medical perspective, even with the latest tests and equipment available. For this reason, a person should not try to diagnose themselves or treat themselves at home, and should seek immediate care and evaluation in an emergency department because a pulmonary embolism has the potential to be fatal.

Diagnosis of pulmonary embolisms has been difficult for many clinicians over the years because making the diagnosis definitively often required placing a catheter in the heart and injecting dye into the pulmonary vessels. As imaging technology has improved, making the diagnosis has become easier especially with computerized tomographic angiography, a.k.a. CT angiography. Patients with chronic pulmonary embolisms may have nonspecific, insidious symptoms so the diagnosis may be delayed, missed or found at autopsy. Currently, the medical literature has urged doctors to place this diagnosis high in their differential diagnosis because of the potential for lethality. Unfortunately the clinical exam is notoriously inaccurate with regards to pulmonary embolism or DVT. Therefore, frequently other tests need to be done. Many of the tests are not specific but yield clues that either point to or point away from the diagnosis of pulmonary embolism. These tests are as follows:

• Chest X-ray (may show other causes for shortness of breath like heart failure or a pneumothorax)
• Electrocardiogram (ECC, EKG - tachycardia and a right strain pattern may occur with pulmonary embolism especially with large central clots)
• CBC (complete blood count; helps to exclude infections)
• D–dimer test (measures breakdown products of blood clots; if negative, suggests there is less chance that the person has a pulmonary embolism; if elevated, it is less useful since many things cause an elevation of this test including many things that may be associated with pulmonary embolism, like pregnancy, cancer, recent surgery, and infection )
• Venous Doppler study (legs or occasionally arms) can confirm the presence or absence of a DVT. In fact approximately 50% of lower extremity DVTs will have asymptomatic pulmonary embolisms.

Usually these tests are done first, if the patient's history and preliminary tests suggest pulmonary embolism, then it is likely that at least one or more tests will be done as follows:

• Pulmonary angiography is the gold standard for diagnosing pulmonary embolism. In this case, a catheter is placed in a large vein in the groin and moved through the right side of the heart in to the main pulmonary artery. Dye is injected and X-rays obtained of the pulmonary vessels. This test is done less frequently these days because of increased sophistication of CTs.
• CT scan of the lungs using a newer generation CT, pulmonary embolism protocol, where dye is injected to visualize the pulmonary arteries; this is not 100% diagnostic for pulmonary embolism but as the newer CTs increase resolution, they are approaching the gold standard angiogram.
• VQ scan (Ventilation – Perfusion scan) uses radiolabeled chemicals that identify the location of inhaled air and match it to the blood flow. If there is good air flow in the lungs but segments of the lung have poor or no blood flow, then this suggests that blood clot may be present. This test is often read as normal suggesting no pulmonary embolus is present. A low probability reading depending on the clinical situation can still have a 30% chance of pulmonary embolism. A high probability reading can have upwards of 90% chance of pulmonary embolism. An intermediate or indeterminate reading falls somewhere in between. The key issue related to this test is referred to as the pretest probability. This means the clinical situation (history, physical, and other supporting tests) may determine to some degree the likelihood of pulmonary embolism. If the possibility for pulmonary embolism is high than the VQ scan is more accurate and vice versa.

When a person goes to a hospital's emergency department or a doctor's office with chest pain or other symptoms that may suggest a pulmonary embolism, remember that the diagnosis has not yet been confirmed, and therefore not all treatment will occur from the beginning of an evaluation.

Patients with chest pain will be placed on a heart monitor, and usually an IV will be inserted, labs drawn and an electrocardiogram (EKG, ECG) ordered.

Some people with pulmonary embolism are critically ill. They have severe shortness of breath, low blood pressure, and low oxygen concentrations. Much more aggressive treatment is undertaken to support or elevate the blood pressure and increase the oxygen in the blood.

The following treatments are the most frequently used for pulmonary embolisms.

• Oxygen can be given in several ways. One is through tubing that is inserted at the tip of the nostrils, called a nasal cannula.
  • If the patient has severely low oxygen levels, he or she will be given a higher flow of oxygen through a mask.
  • Patients may be so short of breath that they require ventilator treatment. A large tube is placed into the trachea (windpipe) and connected to a ventilator (breathing machine), which assists or does the breathing for the patient (the patient will usually be sedated so that he or she is not aware of the procedure).
• Blood-thinning medication may be given, especially in patients with severe symptoms. This is given through an IV, injected into the skin directly, or taken by mouth.
  • Heparin is usually the first medication given. This is given in an IV and works to stop further clot formation from occurring. It is administered continuously through the IV.
  • Another similar medication is called enoxaparin (Lovenox), or a low molecular weight heparin. This medication is given subcutaneously, or just under the skin. It only has to be given every 12 hours, but it does require an injection each time. The current trend is to use low molecular weight heparin for the treatment of pulmonary embolism. Similarly, the pentasaccharide, fondaparineux (Arixtra) may also be used.
  • The oral blood-thinning medication called warfarin (Coumadin) is usually given shortly after the heparin or a low molecular weight heparin is started. The medications are continued until blood tests show that the warfarin is adequately thinning the blood. In very stable patients, much of the drug management can be done in the outpatient setting.
• "Clot buster" medications (also called thrombolytics) are given to those who are critically ill. The purpose is to break up the clot that is blocking the blood vessel in the lung. These medications are used only in those with massive pulmonary embolism, blood pressure collapse, or severely low oxygen that does not respond to treatment. Examples of these medications are reteplase (Retavase), TPA, streptokinase, and urokinase.
• In some life-threatening cases, the patient is taken to a radiologic surgery by an interventional radiologist and a catheter is placed into the pulmonary artery similar to the angiogram described above. This special catheter can break up and suck the clot out relieving the obstruction immediately.

After a patient is discharged from the hospital, they will be monitored very closely by a doctor. Patients need to stay in close contact with their doctor to monitor their condition and make medication adjustments as necessary.

A blood test called the prothrombin time is monitored. Since each lab reagent can potential differ, the patients blood is compared to the labs test blood. The ratio of the patient test value to the lab test value is called the international normalized ratio or INR. This test looks at the level of blood thinning that the medication is achieving. At first, a patient's blood may be checked every few days or weekly. Once the INR stabilizes in the therapeutic range of 2-3, less frequent checks will occur (perhaps every 2-4 weeks).

The best way to prevent a pulmonary embolism is to avoid the risk factors previously discussed.

A frequent cause of pulmonary embolism is a long car or airplane trips when the blood pools in the legs and forms a blood clot that then breaks loose and travels to the lung.

• Stop at least every 2 hours on a car trip and stretch the legs and walk.
• On long airplane flights, get up and walk the aisle at least once an hour to prevent blood clot formation.
• After surgery, compression units are placed on the legs that function like the leg muscles, to help clot formation. Anitclotting medications are also utilized.

The prognosis of people with pulmonary embolism depends on many factors. First and perhaps most significant is the size and location of the clot. The bigger the clot and the larger the blood vessel that is blocked, the more serious the condition is. The outlook may be poor with big clots or clots blocking larger blood vessels, especially if they are not diagnosed and treated quickly.

• Some people may die immediately when a blood clot breaks loose and goes to the lung. Still others die in a short time period because of inability to get oxygen into the blood or from blood pressure collapse.
• Those who do survive the initial episode and who are able to receive appropriate treatment generally do well.
• People with pulmonary embolisms are usually hospitalized for several days until their blood can be adequately thinned. Then they are maintained on blood thinning medication for 6 months or longer. Some patients require life-long medication while others may require a filter surgically placed in the vena cava to prevent large clots from reaching the lungs. These filters are placed in the inferior vena cava, and currently many are of the removable variety. These may be indicated especially in the case where a patient needs surgery or is bleeding and unable to receive blood thinners.