Duplex ultrasound is commonly used to measured vein diameters and patency prior to surgery.
The great saphenous vein in the leg and the cephalic and basilic veins in the arms are conduits that can be harvested and used for leg bypass surgery. These veins need to be free of thrombus and of a minimum size (>3mm) for them to be an effective and lasting conduit for bypassing arterial blockages. B-mode ultrasound is used to measure the diameters of these veins with a detailed report of the vein diameters created. Vascular surgeons will use a vein graft in preference to a synthetic graft due to the longer patency of vein grafts for bypass surgery.
Due to the increasing incidence of renal (kidney) failure the creation of a fistula to be used for dialysis is becoming more and more common. A fistula is created by connecting a superficial vein to the artery. These veins are now subjected to arterial pressure and as a result these veins begin to dilate. The amount blood flow increases through the vein and catheters can be inserted in the vein to take blood to a dialysis machine for filtering and then be returned to the vein. The most common veins used to create a fistula are the cephalic and basilic veins in the arms. B-mode ultrasound is used to map the course of the vein and measure the diameters of the vein. The vein needs to be >3mm in diameter for a successful fistula to be created. At the same time of the vein mapping the brachial, ulnar and radial arteries in the arm will also be scanned to check that there is no flow limiting stenosis in these arteries, the presence of which may compromise maturation of the fistula.
PATIENT PREPARATION AND EXAMINATION TECHNIQUE:
Arm and leg vein mapping: no preparation required.
The patient is seen sitting with the legs dependant and the arms supported by a pillow. The study is non-invasive and painless and does not involve needles. Privacy is assured. The skin of the legs and arms are exposed and gel is applied to the skin. The ultrasound probe is moved over the skin of the limb. B-mode ultrasound is used to examine the veins and assess them for patency and thrombus. The diameters of the veins are measured in the proximal, mid and distal segments of the upper arm and forearm and in the thigh and calf. A detailed worksheet is prepared documenting all diameters and a formal report generated. In the case of vein mapping for fistula creation B-mode and Doppler ultrasound examination of the arm arteries will also be performed with these results included in the formal report.
On occasions the sonographer will draw on the skin the course of the vein as a marker for the surgeon. This should not be removed prior to surgery.
The examination may take up to 30 minutes to perform.
Patency of the vein and presence of thrombus in the veins should be documented.
Presence of calcification and existence stenosis in the arm arteries should be documented.