The term embolus comes from a Greek word meaning “wedge” or “plug.” In the human body, the plug can enter the blood stream from outside the circulatory system (air, amniotic fluid, bone marrow fat) or begin inside the circulatory system, such as venous blood clots or clumps of bacteria infecting heart valves that break off into the blood stream. Once the embolus reaches an artery that is smaller in diameter than the embolus, blood flow past the wedged material will decrease or stop completely.
Recall that we have two hearts, right and left. The right heart supplies blood to the lungs and the left heart to the rest of the body. If an embolus gets to the right heart, it ends up in the lungs and we have a pulmonary embolus. If an embolus comes from the left heart it can end up in the brain (stroke), extremities, kidneys...basically any organ that receives blood from the left heart.
Pulmonary embolus
A pulmonary embolus (PE) causes a ventilation-perfusion mismatch in the lungs. There’s nothing wrong with lung ventilation — the air goes in and out all the way down to the terminal air sacs (alveoli) — but there’s no blood circulation (perfusion) around those alveoli to drop off the carbon dioxide and pick up the oxygen. If it is a small plug, the patient may well be asymptomatic. But if it is a massive plug, the patient may die suddenly.
The most common PE comes from an abnormal blood clot (thrombus) that forms in the large veins in the body (deep venous thrombus or DVT) and breaks off to travel to the right heart and then into the lungs. Most often these form in the legs, but can come from any deep large vein, such as the pelvis or arms. Varicose veins are superficial veins and do not form DVTs that can travel to the lungs.
Presentation
Which of the following patients has a PE?
- A 72-year-old female traveling cross country on a bus who steps off the bus for a break and experiences mild dyspnea and a slight increase in respiratory rate.
- A 32-year-old pregnant female in her last month of pregnancy who has a seizure followed by a cardiac arrest.
- A 52-year-old rancher, whose horse rolls on his left leg leaving behind a femur fracture, who complains of pleuritic chest pain and cough in addition to the leg pain.
- A 23-year-old male boxer with extensive bruising of his right upper arm from a boxing encounter the previous day (you should see the other guy) and complains only of the swollen and tender arm.
The answer: all of them. And that’s the problem. The patient with a PE may be asymptomatic or dead and those in between present with signs and symptoms that don’t necessarily point to the diagnosis. Thus, the PE is often under diagnosed, which is bad because those who survive the first undiagnosed PE (as many do), face a high chance of the next one or two being fatal.
Assessment
Patients presenting with any of the following signs or symptoms should be an indication for you to add a PE as a possibility:
- Dyspnea
- Tachypnea
- Tachycardia
- Hypoxia
- Pleuritic chest pain
- Cough, especially if there is blood
- Painful, swollen extremity (most often the calf)
- Clear lungs on auscultation (remember the lungs are working fine most of the time during a PE, unless there is underlying lung disease or pulmonary edema)
For one or more presenting signs or symptoms above, any of the following historical information you obtain should further cause you to ponder a PE:
- Previous DVT or PE
- Surgery, central venous line or immobilization (bed rest, cast, etc) in the last three months
- Cancer
- Stroke, paralysis or paresis (numbness)
- Smoking
- Obesity
- HTN or chronic heart disease
- Pregnancy
Treatment
In the field, you will support the patient depending on presentation: oxygen for hypoxia, careful handling of tender or swollen extremities, and expeditious transport. Start an intravenous line, collect blood and obtain an EKG if you have these capabilities.
At the receiving facility, your supportive care will be continued while diagnostic testing commences. Depending on the clinical presentation, laboratory evaluation may include an arterial blood gas, clotting studies, cardiac enzymes and a D-dimer (of course everyone gets a complete blood count and basic metabolic panel). The D-dimer measures a breakdown product from blood clots located anywhere in the body. If the D-dimer is negative (low chance of abnormal clots in the body) and there are few signs, symptoms or risk factors for a PE, the likelihood that the patient has a PE is low. If the D-dimer is high, that may or may not indicate the presence of a PE, but does drive further investigation.
The current generation of computerized tomography (CT) scanners can accurately determine the presence of clots in the lungs most of the time. Dye (contrast) is injected through a peripheral vein and subsequently ends up in the pulmonary arterial circulation and allows the CT to visualize the pulmonary arteries and any significant clots. This is called a CT pulmonary angiogram (CT-PA). On those occasions when the CT-PA does not provide enough information, a pulmonary angiogram may be performed. A long catheter is inserted into a central vein, most often the femoral vein, and floated to the pulmonary artery. Contrast is injected directly into the pulmonary artery and X-rays outline the pulmonary circulation, including any sudden stops in blood flow due to clots.
Facility treatment includes inhibition of the clotting process (anticoagulation) and possibly lyses of the clot with fibrinolytics or even surgical removal of the clot. But this chain of events cannot start until a healthcare provider considers the possibility of a PE.
Summary
I think most medical students or residents have heard the following from one or more of their professors: “When you hear hoof beats, think horses, not zebras.” The interpretation of this sage bit of advice is that common things are common; when evaluating a patient, consider common problems first then move on to the rarer conditions. The trouble with a PE is that it occurs more often than it gets diagnosed. It appears to be a zebra, when in reality, it is a horse. Help rid this horse of its stripes by adding PE to your thoughts when you care for the patient with the historical and physical findings described above.
References
- American College of Emergency Physicians. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting With Suspected Pulmonary Embolus. Ann Emerg Med. 2003;41:257-270.
- Goldhaber SZ, Elliot CG. Acute Pulmonary Edema: Part I: Epidemiology, Pathophysiology, and Diagnosis. Circulation; 2003:108; 2726-2729.
- Bosomworth J. Diagnosing Pulmonary Embolism In a Rural Setting. CJRM, 2005;10(2):100-106.
- British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group. British Thoracic Society Guidelines for the Management of Suspected Acute Pulmonary Embolism. Thorax. 2003;58:470-484.