URR Hemodialysis Access Graft Flashcards
what is a hemodialysis AV fistula/graft
surgically created connection between A and V for hemodialysis
-AV fistula is direct connection between A and V that is created to allow access point for dialysis port
-AV graft uses synthetic tube to connect and A to vein to allow access point for dialysis port
what is hemodialysis?
removes creatinine, urea H2O from blood of patients in end stage renal failure
the closer the fistula to the heart, the greater teh risk of developing what?
heart failure
-this is why they are placed at the antecubital fossa and not the shoulder
-the vessels at the antecubital fossa offer the minimum sizes needed for the native vessels, while increasing the distance from the heart
what is included for pre op assessment?
-eval native vessels for selecting graft
-obtain brachial pressures
-brachial and radial eval for stenosis
-vessel diameters measured from inner wall to inner wall
-veins should be evaled to determine if they are straight and located 1 cm of skin surface
-requires allen test prior to graft harvesting and insertion
-distal radial A should demonstrate >50 cm/s
-reactive hyperemia can be performed to assess the feeding A for appropriate increase in arterial diameter and vessel compliance for fistula placement and maturation
what is reactive hyperemia?
-clenching the ipsilateral fist during an upper extrem doppler eval should increase distal resistance and pulsatility in the prox As (high resistance, triphasic flow)
-clenching should be held for 2 mins
-upon release of the clenched fist, distal resistance drops significantly and flow increased to the hand (low resistance, monophasic flow)
-RI is measured and a valve over .7 indicates the feeding A will not work for a successful AVF creation
vessel diameters measured from inner wall to inner wall for pre op assessment?
-requires native vein >2.5 mm for AVF
-native vein > 4 mm synthetic graft
-native artery >2 mm
-tourniquet can be placed on the upper arm to dilate the veins to assess max diameter
indications for post op AVF/AVG eval
-dialysis equipment provides info regarding the functionality of the graft
-palp mass
-significant hand pain
-venous HTN
-water hammer pulse
-decreased or absent thrill; patent graft will produce a thrill - not an indication of normal or abnorm, just patency
what is the water hammer pulse
thumping pulse palpated w/ an acute occlusion of a graft; an occluded graft must be replaced, CANNOT be recanalized
what is the brescia-cimino AVF/AVG?
-most common type
-radial artery to the cephalic vein at wrist
what is the suffbox fistula
-anatomical suffbox is also called the radial fossa
-triangular depression on the lateral aspect of the dorsum of the hand
-radial A, a branch of the radial nerve, and cephalic vein are found in the snuffbox
-radial A is connected to the cephalic V at distal wrist
-because the artery courses directly over the vein in this location, little vessel movement is required during surgery
what is the brachiocephalic AVF/AVG?
brachial A and antecubital V at elbow
what is brachiobasilic AVF/AVG?
brachial A and basilica V at elbow
radiobasilic AVF/AVG?
radial A and basilic V in the forearm
what is a synthetic graft?
-used when native veins are inadequate or an AVF has failed
-PTFE gore-tex made of synthetic polyester
-shorter duration of use and lower patency rates than AVF
straight synthetic graft?
most common; brachial A to basilic V in upper arm
looped synthetic graft?
most common; brachial A to antecubital or cephalic V at elbow; loop extends distally to wrist
what should not be taken on an arm with a dialysis graft/fistula present?
blood pressure
protocol for AVF/AVG
-patient seated with arm extended and supported
-arm externally rotated and placed at a 45 degree angle to the body
-manually palpate the graft for the expected “thrill”
-AVF has single anastamosis site; eval inflow A prox and dist to the fistula, fistula, outflow vein prox and distal to the fistula
1 site of stenosis in AVF/AVG
venous anastamosis
(more common in graft than AVF)
-outflow vein
how does flow look in AVF/AVG?
-venous flow prox to an AVF or AVG becomes pulsatile and turbulent due to the inflow of arterial flow distally
-A flow prox to AVF should be low resistance w/ increased diastolic flow
-norm flow PSV within the graft should be 100-400cm/s
-EDV should be 60-200 cm/s
abnorm findings on AVF/AVG
-graft stenosis suspected w/ velocities greater than 400 cm/s
-velocity ratio= PSV at stenosis / PSV prox to stenosis
-ratio at a stenosis > 2.0 is abnorm
-ratio at the anastomosis > 3.0 abnorm
-if flow velocity doubles between two points in the graft, significant stenosis is suspected
-increase in flow velocity between two segments of 100% or more is abnormal
-if inflow A demonstrates a triphasic waveform, graft occlusion is suspected
-if venous outflow demonstrates loss of spontaneous flow and respiratory phasicity, stenosis or obstruction of the vein is suspected
how to do volume flow
-obtained in straight vein segment, midgraft/fistula is preferred
-measure the diameter of the vein in the area of flow sampling
-measurement obtained by opening sample volume size to include all flow from anterior wall to posterior wall
-abnorm flow volume <500 ml/min indicates stenosis
->1200 ml/min indicates CHF
due to arterial flow hitting venous wall, causes damage to the lining resulting in what?
hyperplasia
complications?
-#1 cause of hemodialysis graft failure is thrombosis of the graft
-stenosis/occlusion
-aneurysm of the graft
-pseudoaneurysm caused by needle puncture for dialysis
-can cause CHF due to increased flow in venous return to heart
-portion of extrem distal to graft may suffer from ischemic symptoms due to steal syndrome
-infection
what is steal syndrome
-most commonly occurs in a radiocephalic fistula
-ulnar A will be antegrade and radial A will be retrograde
-blood travels from the ulnar A into the hand and moves through the palmar arch to exit the hand in the radial A
-caused by high volume flow in most cases, but can also occur w/ inflow stenosis
-both cause flow to be “sucked up into” the radial A and into the outflow vein
-PVR or PPG assessment of the affected digits should be compared to the unaffected digits of the opposite hand
-diminished radial pulse on palpation
-symptoms include pain, polar sensation, paresthesia, finger/brachial index <.8, cyanotic finger tips
-symptoms increase w/ use of the arm
-must be treated by clearing the inflow stenosis or removing the high volume fistula completely in order to prevent permanent damage to the hand/fingers
what does steal syndrome flow look like?
-inflow A w/in the 2 cm prox to the fistula anastamosis site
-inflow A w/in the first 2 cm distal to the fistula anastamosis site
-this waveform is used to diagnose steal syndrome, if flow is retrograde in the distal radial (inflow) A, then flow is moving from the ulnar A through the palmar arch and cephalad toward the radial A/Fistula
-fistula at the confluence of the artery and vein
-outflow vein at multiple locations along the arm, above and below the fistula
