By Victor V Rao MBBS, DMRD, RDMS
Blood clotting is a defense mechanism of the body to prevent excessive blood loss if there is an injury resulting in the disruption of the integrity of the blood vessel wall. However, certain pathophysiological states may activate clot formation in a deep vein in the extremities in the absence of trauma to the vessel wall. Irrespective of the mechanism, clots that form inside a deep vein in the extremities, is known as a Deep Vein Thrombosis or DVT. The DVT by itself is not as sinister as the pulmonary embolism (PE) that can potentially occur as a complication of a DVT.
PE is a condition where the blood clot from a deep vein in the extremities breaks off and moves through the circulation and reaches the right heart. Eventually, the clot reaches the pulmonary circulation and blocks the blood supply to the lungs, where the exchange of gases occurs.
Small clots could be asymptomatic or could result in mild symptoms such as chest pain, cough, and hemoptysis. If the clot size is hemodynamically significant, it can cut off the supply of blood to a vital segment of the lung with devastating results and may even lead to death.
Around 400 BC, Hippocrates reported that he observed that the blood of a wounded soldier congealing as it cooled. Aristotle recorded that blood removed from the body underwent a decay process that resulted in the formation of a blood clot. He postulated that the clotting was probably a result of the blood cooling down.
It was not until in the 1600s that Mercurialis observed and reported the formation of blood clots in blood vessels at normal body temperature. In the 1900s, Paul Marowitz hypothesized the existence of a coagulation pathway and suggested the presence of multiple clotting factors to form a blood clot inside a blood vessel. Medical researchers have discovered several other coagulation factors since then.
The first documented case of DVT was reported in 1271 involving a patient with unilateral leg swelling and edema. The individual survived and lived for several years after the incident, probably because of spontaneous resolution of the DVT or non-progression into the deep veins above the popliteal crease or no hemodynamically significant PE. Subsequently, other cases were documented with a predominance in pregnant and post-partum women.
In the 1930s, three factors were identified that could potentially cause a DVT — venous stasis, vessel wall injury, and hypercoagulability. These are known as Virchow’s triad. It should be noted that many other factors could result in a DVT. In some cases, it could even be an unknown cause. The symptoms also vary widely from being totally asymptomatic to various degrees of pain, redness, and swelling of the involved extremity.
Unfortunately, the physical exam is not very sensitive to diagnose a DVT. The gold standard for diagnosing a DVT is contrast venography with very high sensitivity and specificity of 100%. Diagnostic ultrasound is effective in diagnosing a DVT in the lower extremities. Recently, point-of-care (POCUS) ultrasound with a limited 2 or 3 zone protocol, has been shown to have a high degree of accuracy in diagnosing a DVT in the lower extremities when paired with D-dimer and a follow-up POCUS exam within a week.
The advantage that POCUS offers is the ability to make a prompt diagnosis in the point-of-care setting and initiating anticoagulation therapy when indicated without unnecessary delay. Keep in mind that the value of the POCUS DVT assessment is in the positive exam. Being able to diagnose a DVT and to be able to initiate anticoagulation therapy immediately is going to be a game-changer. It should end up significantly lowering mortality and morbidity rates.
Fortunately, the anatomy of the deep veins for the limited protocol is somewhat elementary to understand and evaluate. It is imperative to be able to identify the deep vein anatomy and any venous anatomical variants such as duplication of the deep veins. The venous compression using B-mode or 2D ultrasound is the gold standard technique.
Make sure the compression is performed only in the transverse view of the vein being evaluated. The vein position should be in the middle of the image. Color Doppler is an adjunctive mode to identify the clot outline and also if the clot is not entirely obstructing the lumen of the vessel. If it is completely blocking the flow in the vein, then there would be no color Doppler signal seen in the affected segment of the vein.
This protocol does not rule out the possibility of a clot in the iliac veins or the IVC. However, by adding spectral Doppler evaluation of both common femoral veins and observing the normal phasic venous flow pattern, we could potentially eliminate or reduce the chance of a hemodynamically significant blood clot in the vessels mentioned above.
A non-phasic venous flow could suggest the possibility of a clot in the IVC or iliac veins. Keep in mind that it could also be a result of extrinsic compression of the vessels mentioned above.
Currently, PE results in 60,000 – 100,000 deaths per year in the USA. The expectation is that up to 900,000 individuals could be affected by DVT/PE each year. Up to 10 – 30% of individuals with a PE will die within a month of diagnosis, and unfortunately, 25% of patients with a PE may die suddenly. Therefore, every physician and healthcare worker should be trained to diagnose this condition using POCUS. It has the potential to significantly alter the death rate as this is a preventable cause of death if detected early before a large embolus affects the pulmonary circulation.
POCUS for lower extremity DVT evaluation using the two zone protocol can be learned in just a few minutes and mastered over a few hours and days. Once the anatomy is understood and the technique is developed well, then it is straightforward to master this assessment. POCUS DVT is one of the most critical skills to acquire, as it will save lives and help lower mortality rates in patients with DVT.
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