This lesson will discuss a condition known as deep vein thrombosis, including the three main reasons for its formation, as well as its very famous and deadly complication: a pulmonary embolism.
How the Lungs and Legs Are Related
When you jog or run, your legs move fast and you breathe more quickly. If you didn’t breathe more quickly, then not enough oxygen would get down to your legs in order to power the energetic processes that help your legs move more quickly in the first place. Interestingly enough, although your legs are clearly dependent on your lungs, sometimes a disease process can arise within them that actually ends up harming the lungs that are so critical to movement!
Deep Vein Thrombosis
The problem that occurs most commonly in the lower extremities is known as deep vein thrombosis.
Deep vein thrombosis is easy to define because it’s exactly what it sounds like; it’s the formation of a blood clot in veins deep within the body. Again, most commonly, veins deep within the legs. Since a thrombus refers to a blood clot, it makes sense why the definition matches the term itself.Classically, the reasons for venous thrombosis have been called Virchow’s triad. They’re named after Rudolph Virchow, a German doctor, who came up with them.
The triad consists of:
- Injury to the inner wall (endothelium) of the vein, as a result of things like trauma, infection, and even metabolic disease. Just like if you were to injure your skin, a small clot would form to prevent bleeding out. So, too, if your vein is injured, a clot will form to prevent bleeding out.
- Another aspect of Virchow’s triad is venous stasis, meaning the blood doesn’t move around very well in these veins due to a lack of motion (such as that following surgery or long airplane rides), heart conditions, oddly-shaped red blood cells, shock, and so on.
- And the final aspect of the triad is the activation of coagulation, or hypercoagulability, as a result of everything from cancer to kidney disease to genetic defects.
One, now mainly outdated sign, a sign that was traditionally used to help diagnose the presence of deep vein thrombosis, is known as Homan’s sign. This sign is elicited if a person experiences pain in the calf when there is dorsiflexion of the foot while a patient is lying on their back. So, if you were lying down completely flat on your back and someone flexed your foot at the ankle upwards, towards your head, and you experienced calf pain, that would be called a positive Homan’s sign. Deep vein thrombosis can cause a person to feel quite a bit of pain, as you can now guess, as well as swelling, warmth, and redness in the affected area.
Troublingly, pain isn’t the only problem people with DVT (deep vein thrombosis) may experience. In fact, it’s the least of their worries. The blood clot that forms in a deep vein in the leg may have part of it break off.
Part of a thrombus that has broken off and traveled to another part in the body is known as an embolus.The embolus (plural: emboli) can travel to the lungs, resulting in a pulmonary embolism. A pulmonary embolism is a complication arising from deep vein thrombosis that results in a blood clot blocking the pulmonary artery or its branches. This can cause difficulty breathing, hypoxemia (which is low oxygen in the blood), pain in the area where the clot has lodged itself, damage to the lung, a cough, and even death. A pulmonary embolism should never be taken lightly.
Diagnostics and Treatments
To diagnose DVT, which can lead to pulmonary embolism, blood tests can measure how well the blood is clotting or they can measure d-dimers, which are clot degradation products.
Their elevations are an indicator that there is a lot of clot formation going on, since you can’t have clot degradation products without first forming a clot that can be degraded. You can equate this to water, our blood, and an ice cube, our solid clot. As the ice cube falls apart and melts, little pieces of ice, our d-dimers, will be released. But those little pieces of ice could never have formed had the water not frozen in the first place!Furthermore, ultrasound may be used to help visualize a clot, and other imaging techniques such as a venography, CT, or MRI scans can help look for the location of the clot.
Many of these same visualization techniques, in addition to an X-ray, can be used to help visualize a pulmonary embolism or rule out other disease processes that may mimic this complication of DVT.Treatment for these two conditions includes anticoagulants (a.k.a. blood thinners) that help prevent new clot formation in addition to medications (called thrombolytics) that break up clots. However, thrombolytics must be used with extreme caution as they can result in serious bleeding or life-threatening emboli in some situations. Patients with a history or predisposition to DVT may also wear compression stockings to help prevent clot formation.
In summary, we discussed deep vein thrombosis, which is the formation of a blood clot in veins deep within the body. Again, most commonly veins deep within the legs. DVT occurs classically due to something known as Virchow’s triad, which refers to:
- Injury to the inner wall of the vein
- Venous stasis, and
- The activation of coagulation, or hypercoagulability
A sign that was traditionally used to help diagnose the presence of deep vein thrombosis is known as Homan’s sign. This sign is elicited if a person experiences pain in the calf when there is dorsiflexion of the foot while a patient is lying on their back.DVT can lead to a pulmonary embolism.
A pulmonary embolism is a complication arising from deep vein thrombosis that results in a blood clot blocking the pulmonary artery or its branches. An embolus is a part of a thrombus that has broken off and traveled to another part in the body. A pulmonary embolism, remember, is a life-threatening condition. Both of these conditions can be diagnosed with blood tests and imaging modalities, and their treatments include blood thinners and medications that break up clots.
Once you are done with this lesson, you should be able to:
- Define DVT and recall how it is caused and diagnosed
- Explain how deep vein thrombosis can lead to a pulmonary embolism
- Explain how to treat DVT and pulmonary embolism