Haemodialysis vascular access is required in patients with end-stage renal failure. Usually, it is an upper limb vascular access on the non-dominant side. Central venous access and lower limb access (less frequent) are other options.
Types of vascular access
- Native arteriovenous fistula (AVF): preferred access as it has better outcomes. The desired artery and vein are connected to each other in one of three of these fashions:
- Synthetic polytetrafluoroethylene (PTFE) graft: can be used in case of unsuitable vascular anatomy of the patient or after the failure of an AVF.
Preoperative evaluation (ultrasound)
Color Doppler ultrasound has largely replaced angiography in imaging of hemodialysis vascular access (although the latter is considered the gold standard imaging modality) being an available bed-side technique and due to its low cost, lack of radiation and contrast media.
Color Doppler ultrasound is used for preoperative evaluation of the vascular anatomy before the creation of vascular access and postoperative evaluation of the maturation of the vascular access and diagnosis of the related complications.
The patient is examined in supine position with the upper limb in neutral anatomical position. The hand is relatively dependent (hanging from the side of the bed).
The superficial veins are scanned for patency and course. Multiple measurements of the diameters of the veins and distance form skin should be obtained. The suitable veins should be marked on the skin surface. The veins with a diameter >0.2 cm (0.25 cm if a tourniquet is applied) and distance form skin <0.6 cm have better outcome regarding the maturation of the AVF and vessel cannulation respectively.
The deep veins are scanned for patency using compressibility until the peripheral part of the subclavian vein. The central veins can be indirectly assessed by Doppler wave pattern analysis (venography may be required if central venous stenosis or occlusion is suspected).
The arteries are scanned for patency, stenosis and variants. A high bifurcation of the brachial artery is a common variant.
Arterial wall compliance can be evaluated by Doppler. The triphasic wave pattern recorded in the radial artery with a clenched fist should normally become biphasic with a resistance index (RI) <0.7. RI >0.7 and arterial diameter (inner-to-inner edge) <0.2 cm are poor prognostic factors for the maturation of the AVF.
Postoperative evaluation (ultrasound)
AVF maturation and access volume flow
Volume flow across the feeding brachial artery for AVF and along PTFE graft is measured by machine-based software using the formula (area x mean velocity x 60, where area is the cross-sectional area of the vessel in cm2).
Automatic calculation of the volume flow can be obtained by equipment software after measuring the inner diameter of the brachial artery/graft, placing a sample volume covering the entire luminal cross-section, using Doppler angle ≤60° and defining the time of the cardiac cycle.
AVF volume flow <300 mL/minute is suggestive of AVF failure.
PTFE graft volume flow <650 mL/minute is suggestive of graft failure.
Thrombosis and aneurysm formation
Thrombosis is the most common cause of vascular access failure. Usually, it is seen along the out-flow vein or the graft itself.
Vascular access stenosis
- AVF: high resistance Doppler wave pattern in the brachial artery or reduced flow volume is suggestive of hemodynamically significant stenosis
- PTFE graft: luminal diameter reduction >50% or a peak systolic velocity (PSV) >400 cm/second is suggestive of hemodynamically significant stenosis
- postoperative hematoma may cause external compression and lead to stenosis
Steal syndrome (access-induced ischemia)
The steal phenomenon is converted into a steal syndrome (painful limb at rest or during hemodialysis) when compensatory mechanisms to maintain peripheral arterial perfusion fail.
The access-feeding artery is evaluated by color Doppler for a change in the flow direction. The flow in the distal arterial tree usually improves with transient occlusion of the AVF during the examination.
- high-output cardiac failure may occur with AVF flow volume >2000 mL/minute
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- 2. Wiese, Patrick, Nonnast-Daniel, Barbara. Colour Doppler ultrasound in dialysis access. (2004) Nephrology Dialysis Transplantation. 19 (8): 1956. doi:10.1093/ndt/gfh244
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