Introduction
Saphenous vein mapping is an ultrasound procedure used to visualize the location, course, and quality of the saphenous veins of the leg before bypass graft surgery. The saphenous vein is a large leg vein that drains deoxygenated blood from the leg and sends it to the heart. The saphenous vein is divided into a great saphenous vein (vein which runs along the front side of the leg) and a lesser or small saphenous vein (the vein that runs along the backside of the leg). Doppler ultrasound imaging is commonly used to detect the speed and direction of blood flow. Ultrasound is used to locate the saphenous vein, which is superior to the clinical examination (detection of veins).
What Are the Uses of Saphenous Vein Mapping?
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To determine the vein size and location.
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To detect venous thrombosis (blockage of veins by the blood clot).
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To assess the venous reflux (backward flow of the blood collected in the lower leg).
What Is the Function of a Doppler Ultrasound?
Soft tissue images of the body are captured with the help of a diagnostic tool called ultrasound or sonogram. The ultrasound produces and passes high-frequency sound waves into the body through a probe known as a transducer. The produced sound waves are reflected by the targeted organs and are again captured by the transducer. The captured sound waves are transformed into images with the help of a computer.
Doppler ultrasound, called a duplex study, is a special ultrasound technique in which the sound waves are audible during the scan. The difference in the blood cells' movement results in variation in the pitch of the reflected sound waves; it is referred to as the doppler effect. The images are processed as graphs or color pictures on the computer. Routine ultrasound shows only the structures of the organs but cannot show the blood flow.
How Is Saphenous Vein Mapping Performed?
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During the saphenous vein mapping procedure, patients are asked to lie on their backs with their hands on their sides on the procedure table. Patients are placed in the lateral decubitus position for small saphenous vein mapping. The procedure room should be maintained warm at a temperature of about 18 to 22 degrees Celsius. For this procedure, a tourniquet is tied over the upper thigh, or the patients are placed in a reverse Trendelenburg position (a position in which the patient's head and the chest are raised at 30 degrees) which helps in the venous filling. A tourniquet is a band tied over the legs or arms to reduce the blood flow to the heart. Tourniquet causes the occlusion of the vessel wall, and pooling of blood in leg veins results in distension (enlargement) of the veins. It makes the veins easily palpable during the procedure. For better visualization, the leg is flexed and rotated externally. Patients might be asked to drink plenty of water before the procedure, which helps visualize the veins.
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Then, the radiologist will apply a generous amount of water-soluble gel over the leg. Then the specialist may glide the probe (transducer) over the skin. A transducer with a frequency ranging from 5 to 7 MHz is used for saphenous vein mapping. When the transducer is moved back and forth, images are produced. The transducer is placed at a depth of about 2.8 cm below the knee and increases the depth when reaching the thigh. The gel is then wiped off later. Saphenous vein mapping does not cause any pain, but the patients can feel the transducer's pressure while placing it over the leg.
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The course (path) of the entire vein is marked on the medial aspect of the leg. Doppler ultrasound confirms the vein by its tubular structure and compressible nature. The measurements of the vein are marked at multiple sites using a surgical marker which helps the surgeon to harvest the vein. The patient should not disturb the markings until the surgery. The saphenous vein mapping is done in both legs. This procedure usually takes three to five minutes per leg and sometimes longer when the bridging technique is used. The bridging technique replaces the traditional method of a long continuous incision with a smaller incision.
What Is the Role of Saphenous Vein Mapping in Coronary Artery Bypass Graft (CABG)?
The coronary artery bypass graft is a surgical procedure used to treat blocked or narrowed coronary arteries resulting in coronary artery disease. In this procedure, the surgeon reroutes the blood flow around the blocked vessels by harvesting arteries or veins from other body parts, usually from the legs, arms, or chest. The great saphenous vein is often harvested for coronary bypass graft procedures. This procedure can be done as open cardiac surgery or minimally invasive using the laparoscopic camera with smaller incisions.
What Are the Limitations of Saphenous Vein Mapping?
Saphenous vein mapping cannot be performed in the following conditions:
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Varicose veins (enlarged and twisted veins, most commonly in the legs).
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Large bifurcations (a division of the central vein into two venous branches).
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Patients underwent varicose vein stripping (a surgical procedure used to remove enlarged veins from the legs).
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Severe swelling in the legs.
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An existing open wound or surgical staples in the procedure site.
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Obesity (overweight).
Conclusion:
Doppler ultrasound is the standard imaging technique used for saphenous vein mapping procedures. Saphenous vein mapping prevents unnecessary damage to the soft tissues in the leg. This procedure acts as a guide to locating the appropriate vein for great saphenous vein harvest. This technique visualizes the accurate location of the vein and makes the vein mapping procedure quick and more accessible. Saphenous vein mapping prevents multiple incisions and excessive tissue dissection that affects the quality of the harvested vein. In addition, this procedure prevents complicated postoperative wounds.
