Hemodialysis vascular access

Vascular access for hemodialysis is used for end-stage renal failure that requires renal replacement therapy. Options include temporary/permanent and non-surgical vs surgical methods. This article will focus on surgical arteriovenous fistulae.

Types of vascular access

Temporary

• temporary vascular access dialysis catheter 

  • inserted into a central vein (internal jugular or femoral veins) under ultrasound guidance

  • these lines are usually removed after 7-10 days due to the risk of infection

Permanent

Non-surgical

• permanent tunneled hemodialysis catheter

  • a long term alternative, usually inserted into either the internal jugular or subclavian veins

Surgical

Usually created in the non-dominant arm. 

• native arteriovenous fistula (AVF) is the preferred option as it has better outcomes. The three main types are: 

  • radiocephalic AV fistula 

  • brachiocephalic AV fistula

  • brachiobasilic transposition AV fistula

• synthetic polytetrafluoroethylene (PTFE) graft: can be used in case of unsuitable vascular anatomy, or after the failure of a pre-existing AVF

Minimally invasive

• endovascular arteriovenous fistula creation: an emerging endovascular alternative to surgical AVF creation

Radiographic assessment

Preoperative assessment

Preoperative assessment of venous anatomy is essential in the selection of the most appropriate approach. Doppler ultrasound has largely replaced venography for this, as it is a quick and ionizing radiation-free alternative (although venography remains the gold standard). Doppler ultrasound can also be used to assess fistula maturation and potential complications such as stenosis and thrombosis.

Venous ultrasound

The patient is examined in the supine position with the upper limb in a 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 from the 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 from skin <0.6 cm have better outcomes regarding the maturation of the arteriovenous fistula 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).

Arterial ultrasound

The arteries are scanned for patency, stenosis and variants. A high bifurcation of the brachial artery is a common anatomic variant.

Arterial wall compliance can be evaluated with Doppler. The triphasic wave pattern recorded in the radial artery with a clenched fist should normally become biphasic with a resistive 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 arteriovenous fistula.

Postoperative assessment

AVF maturation and access volume flow

Volume flow across the feeding brachial artery for arteriovenous fistula and along PTFE graft is measured by machine-based software using the formula (area x mean velocity x 60, where the 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

Complications

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/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 arteriovenous fistula during the examination.

Heart failure

• high-output cardiac failure may occur with AVF flow volume >2000 mL/minute