Hemodialysis access graft

AV fistula

A direct connection between an artery and vein that is created to allow access point for dialysis port

AV graft

Uses a synthetic tube to connect an artery and vein to allow an access point for diapysis port

Hemodialysis

Removes creatinine, urea and water from the blood of pts in end-stage renal failure

The closer the fistula to the heart, the greater the risk for…

Developing heart failure

Pre-op assessment for AV fistula

Eval native vessels for selecting appropriate type of graft

Obtain bilateral brachial pressures (should be <20mmHg between both)

Native vein should be >2.5mm for AVF

Native vein >4mm for synthetic graft

Native artery >2mm

Veins should be evaluated for a straight course and within 1cm of skin surface

Requires Palmar arch test

Reactive hyperemia can be performed to assess the feeding artery for appropriate increase in arterial diameter and vessel compliance for fistula placement and maturation

Reactive hyperemia

Clenching the ipsilateral fist during an upper extremity Doppler evaluation should increase distal resistance and pulsatility in the proximal arteries

The clenching should be held for 2mins

Upon release of the clenched fist, the distal resistance drops significantly and flow increases to the head

The RI is measured an a value over 0.7 indicates the feeding artery will not work for successful AVF creation

Indications for post-op AVF/AVG evaluation:

Dialysis equipment provides information regarding then functionality of the graft (dynamic venous pressure (>200mmHg), access recirculation (>12% ABNL), urea reduction ratio (<60% ABNL))

Palpable mass, significant hand pain, venous HTN, water hammer pulse (thumping pulse palpated with acute occlusion of graft)

Decreased of absent thrill = abnormal

Brescia-Cimino

Most common AVF

Radial artery to the cephalic vein at wrist

Snuff box fistula

Anatomical suffbox is also called the radial fossa

Triangular depression on the lateral aspect of the dorsum of the hand

The radial artery, a branch of the radial nerve, and the cephalic vein are found in the snuffbox

Radial artery is connected to the cephalic vein at distal wrist

Because the artery courses directly over the vein in this location, little vessel movement is required during surgery

Brachiocephalic AVF

Brachial artery and antecubital vein at elbow

Brachiobasilic AVF

Brachial artery and basilic vein at elbow

Radiobasilic AVF

Radial artery and basilic vein in the forearm

Synthetic graft

Used when native veins are inadequate or an AVF has failed

PTFE Gore-Tex graft - made of polytetrafluoroethylene, also known as Teflon

Dacron graft - made of synthetic polyester

SHORTER DURATION THAN AVF and LOWER PATENCY RATES

Straight synthetic graft - MOST COMMON; brachial artery to basilic vein in upper arm

Looped synthetic graft - MOST COMMON; brachial artery to antecubital or cephalic vein at elbow; loop extends distally to wrist

Arm position for Fistula evaluation

45 degree angle and externally rotated

AV fistula has a ______ anastomosis site

Single

An AV graft has ________ anastomosis sites

Two

Venous flow proximal to an AV fistula

Becomes pulsatile and turbulent due to high inflow of arterial flow distally

Arterial flow proximal to AV fistula should be…

Low resistance with increased diastolic flow

Pressure will decrease in the artery distal to fistula

Normal flow PSV in AV graft

100-400cm/s

Normal EDV in AF graft

60-200cm/s

Abnormal findings in graft

Graft stenosis suspected with velocities greater than 400cm/s

Velocity ratio = PSV at stenosis/PSV artery prox to stenosis

Ratio at stenosis >2.0 is abnormal

If the flow velocity doubles (or more) between two points in the graft, significant stenosis is suspected

Increase in flow velocity between two segments of 100% or more is considered abnormal

The inflow artery demonstrates a triphasic waveform, graft occlusion is suspected

If the venous outflow vein demonstrates loss of spontaneous flow and respiratory phasicity, stenosis or obstruction of the vein is suspected

Volume flow

Obtained in a straight vein segment, midgraft/fistula is preferred

Measure the diameter of the vein in the area of flow sampling

Doppler measurement obtained by opening sample volume size to include all flow from anterior wall to posterior wall

Abnormal flow volume <500ml/min indicates stenosis

>1200ml/min indicates CHF

Most common sites of dialysis graft stenosis

Venous anastomosis

Outflow vein

Due to arterial flow hitting venous wall, causes damage to lining resulting in hyperplasia Complications:

#1 cause of hemodialysis graft failure is THROMBOSIS of the graft

Stenosis/occlusion

Aneurysm of the graft

Pseudo caused by needle puncture for dialysis

Can cause CHF due to increased flow in venous return to heart

Portion of extremity distal to graft may suffer from ischemic symptoms due to steal syndrome

Infection

Dialysis access steal syndrome most commonly occurs in a

Radiocephalic fistula

Dialysis access steal syndrome

Distal to the fistula graft, the ulnar artery will be antegrade and the radial artery will be retrograde

Blood travels from the ulnar artery into the hand and moves through the palmar arch to exit the hand in the radial artery

Caused by high volume flow in most cases, but can also occur with inflow stenosis

Both cause flow to be “sucked up” the radial artery and into the outflow vein from the ulnar/palmar arch

PVR or PPG assessment of the affected digits should be compared to the unaffected digits of the opposite hand

Symptoms of Dialysis access steal syndrome

Include increasing pain, polar sensation, paresthesia, Finger/Brachial Index <0.7, cyanotic fingertips

Symptoms increase with use of the arm

Diminished radial pulse on palpation

Duplex eval of Dialysis access steal syndrome

Inflow artery within the 2cm proximal to the fistula anastomosis site

Inflow artery within the first 2cm distal to the fistula anastomosis site

• This waveform is used to diagnose steal syndrome, if flow is retrograde in the distal radial (inflow) artery, when flow is moving from the ulnar artery through the palmar arch and cephalad toward the radial artery/fistula

• Blood is bein STOLEN from the hand before it is perfused properly

Fistula at the confluence of the artery and vein

Outflow vein at multiple locations along the arm, above and below the fistula

Segmental pressure evaluation

Can only be performed when the wrist cuff can be placed distal to the fistula

In the average sized pt:

• 12cm cuff placed on the unaffected upper arm

• 10cm cuff placed at the wrists

• 2.5cm cuffs placed on the fingers

PPG sensors placed bilaterally on digits

Unaffected arm: Brachial, radial, ulnar and digital waveforms and pressures obtained

Unaffected arm: Radial, ulnar and digital waveforms and pressures obtained

Outflow vein is compressed

Outflow vein compression normal findings:

Causes multiphasic flow patterns in the brachial, radial and ulnar arteries

Digital waveforms should demonstrate consistent amplitude and vary by less than 15mmHg between digits

Digital/Brachial index >0.7

Positive for Dialysis access steal syndrome:

Digital pressures <80mmHg and DBI <0.7

Compression of outflow vein causes increased amplitude of the digital waveforms of the affected arm and an increase in the digital pressures

The increase in pressure and amplitude is caused by the compression of the outflow vein because normal flow is returned to the hand as outflow is obstructed

What is the difference between a hemodialysis fistula and a hemodialysis graft?

A fistula connects a native artery and vein, a graft is a synthetic vessel connecting an artery and vein

The minimum diameter of a native vein that can be used for a hemodialysis fistula is ______, while the minimum diameter of the native vein that will connect to the synthetic vein that will connect to the synthetic graft is __________

2.5mm; 4mm

What is the minimum arterial diameter that can be used for connection to a hemodialysis graft?

2mm

What pre-procedure test is required before creation of a dialysis fistula

Allen test

A patient presents for evaluation of their AVG and the script states “water hammer pulse present” What do you expect to find on the exam?

Occluded graft

What is found in the anatomical snuff box

Distal cephalic vein, distal radial artery, radial nerve

What determines if a fistula is created, or a graft is inserted for dialysis?

If the native vessels are too small for a fistula, a graft is used instead

What is the most common site for stenosis in pts with AVG

Venous anastomosis

What changes occur in the native artery proximal to an AVF?

Flow changes from triphasic to monophasic

What changes occur in the native vein proximal to an AVF?

Increased pulsatility

What is the most common cause of AVG failure?

Thrombosis

How is the volume flow measured in an AVF?

Open the sample volume from wall to wall within a normal segment of the graft and trace the waveform

If the radial and ulnar artery demonstrate flow moving in opposite directions in a pt with an AVG, it is highly suggestive of:

Steal syndrome