Vascular Evaluation before Hemodialysis
Vascular mapping involves evaluation of arterial and venous upper extremity systems before vascular access for hemodialysis is placed. This is done in an attempt to reduce failure rate of AV fistulas and grafts due to infection, thrombosis and stenosis and AV fistula failure to mature. Selection of suitable vessels via pre-operative vascular mapping is recommended before creating vascular access for hemodialysis.
There are several methods for vascular mapping, and generally it is recommended that a physical evaluation should be combined with one of the other methods, for more accurate results, especially in cases of obese patients or those with a history of prior vascular access.
Common vascular mapping methods before hemodialysis
Physical examination before vascular mapping for hemodialysis patients
- A detailed medical history must be taken
- By placing a tourniquet on the upper extremity, veins will be assessed as to their caliber, length of straight segment suitable for cannulation and distance of vein from skin surface.
- Pulses and blood pressure in both extremities should be tested. Patient should have less than 20 mmHg differential in blood pressure between the two arms.
- The Allen test, for assessment of the patency of the palmar arch, should be done. Use of vascular Doppler can increase the effectiveness of the Allen test predicting collateral perfusion of the hand. In order to perform the Allen test, patient should stand with arms extended, palms turned upward. With the radial and ulnar arteries compressed firmly a fist should be made repetitively. After compression is released the physician will watch for change of color in palm.
- Physical evidence such as scars must be documented. Chest, breast and upper arms should be evaluated for swelling or collateral veins.
Angiography for hemodialysis
Direct imaging of the central veins, via use of radiocontrast. Allows for assessment vein diameter, length and patent draining and central veins. Conventional iodine venography may cause renal deterioration, so a low iso-osmolar contrast such as gadolinium is used. Tourniquets are applied, and the contrast is injected. Images are obtained using calibrated pulse fluoroscopy.
A noninvasive and objective assessment of the arterial and venous systems.
The forearm is held 45 degrees away from body and the internal diameter wall thickness and arterial flow are calculated, and abnormalities in the upper extremity arteries noted. Additional parameters include vessel depth and Doppler flow through the vessel. Draining and central veins are assessed for stenosis and thrombosis.
Color flow Doppler is considered to be the best method of visualizing veins, primarily because radio contrast is not needed. However, ultrasonography does not offer a direct evaluation of the central venous vasculature, and additional techniques may need to be used, especially with high risk patients such as patients who have used/are using a catheter for hemodialysis access.
For more information regarding vascular access for hemodialysis and improving AF fistula success rates using VasQ, please refer to our website.