An “embolus” is a blood clot that floats downstream from another location. The plural is “emboli.” The disease Pulmonary Embolism (PE) means a clot in the lung, which can kill if it’s a big one.
A PE usually comes from a vein in the leg or pelvis. A piece breaks off, which floats through the blood stream to the heart, then gets stuck in the lungs where it cuts off circulation. By the way, bruises (black-and-blue marks, often from injuries) are clotted blood under the skin, but not within a vein. So that kind of clot can’t float anywhere, & is no danger whatsoever.
We mostly think about PE if a patient has shortness of breath (SOB) [this is a standard medical abbreviation]. It can also cause chest pain with each breath (“pleuritic”). One study found that among patients with pleuritic chest pain, breathing less than 20 times per min., and no SOB, only 4% had a PE. It’s not 0%, but still reassuring, in the sense that a PE is not a common cause of chest pain among patients who don’t appear very ill.
There are two main clues to a PE:
1. The symptoms begin all of a sudden (within 1-2 minutes in 75% of cases); AND/OR
2. The patient has risk factors for blood clots. These are:
- signs of a leg clot: pain, tenderness, or swelling of inside area of upper thigh; or just new swelling in just one foot (very rarely, a swollen arm)
- Immobilization for ≥3 days (e.g. leg cast)
- General anesthesia within the past 4 weeks
- Active cancer (that’s almost always been already diagnosed)
- Prior history of either leg clot or PE.
- Pregnancy, or under 3 months post-partum
- HIV infection, though not usually listed, predisposes to blood clots.
Other concerning findings, not as common or as diagnostically strong, include:
- Rapid heart rate (Tachycardia)
- Rapid respiratory rate
- Coughing up blood
- Obese women with hypertension who smoke
Patients with possible PEs get sent to the ER, for a blood test “D-dimer”, a chemical produced by clots & many other conditions. If it’s negative, there’s no PE. A positive D-dimer doesn’t prove PE, but then the ER clinicians will add up risk factors to see what the probability might be. If there’s a decent chance, they’ll do a special CT scan with dye (a “CT-angiogram”), or maybe a “V/Q scan” (see below).
Why not just do those tests anyway? Partly to avoid radiation exposure, unlikely risks of the CT dye, & expense. But mostly because they’re not perfect; each gives a certain number of false-positives. Then we’re stuck prescribing anticoagulants (“blood thinners”), with their risk of hemorrhage, or ordering an invasive pulmonary angiogram to be sure (slight risk of causing a PE, or death). Read why to Never Order Tests if there’s Low-Probability of Disease.
By the way, for the rare condition Chronic PE, the “Ventilation / Perfusion Scan” (“V/Q scan”) may be better than the CT (many clinicians don’t know this). It can identify areas of the lung which get plenty of oxygen (ventilation), but don’t get perfused with blood, meaning something is blocking the circulation (a chronic clot!). The “Q” in the abbreviation is the mathematical notation for “streamflow.”