Hemodialysis Access Grafts & Fistulae (Lana)

why does one get a hemodialysis access grafts and fistulae

incidence of chronic kidney disease and end-stage renal disease is increasing in USA

goal of access grafts and fistuale

to provide long term hemodialysis access with a low frequency of reintervention and low complication rate

access grafts and fistuale eliminates undesirable effects of:

eliminate excess fluid
decreases undesirable substance in the body

which arm are fistulae planted in?

non dominant

why the non-dominant arm

preserves proximal vessels for potential future access

why are fistulas planted distally?

the success rate is higher
and if that region fails, then one can keep working up the arm using proximal vessels

and allows for patient to carry out normal daily activities

success rate of the distal fistulae?

60-70%

why arms are used for fistulae?

legs have higher risk for infection

what is dialysis used for?

treatment for renal failure

what is dialysis exactly?

a method for filtering the blood externally

how is the blood filtered externally in dialysis?

blood is removed from the artery
filtered through the dialysis machine
and returned to the body via the vein

dialysis is accomplished by?

creation of AVF

what exactly is a dialysis access?

a connection between an artery and a vein

how often are dialysis access areas used?

2 needles, 3x per week

fistulae or graft: which has better long term patency?

fistulae

T or F
fistulae have a lower maturation rate

TRUE

T or F
fistulae have a early thrombosis rate

TRUE

AVF 2 year success rate

40-60%

AVG 2 year success rate

18-30%

pre-op access includes:

vein mapping
duplex assessment

synthetic graft makeup

PTFE
or teflon

PTFE

poly tetra fluoro ethylene

function of synthetic grafts

connect an artery to a vein

can synthetic grafts be looped or straight?

YES
both

what is a native autogenous fistula?

a vein is connected directly to an artery
NO TUBING

how does a native autogenous fistula work?

the fistula will mature and the vein dilates in response to the arterial pressure

types of native autogenous fistula

breccia-cimino

breccia cimino connection

radial artery to cephalic vein

cephalic vein location

lateral part of arm

basilic vein location

medial in arm

transducer used for scanning:

5-10 MHz

what is evaluated first for pre-grafts?

arterial system

when can venous system be scanned, after arterial?

when diameters > 2mm with no significant abnormalities then venous can be scanned

venous, AVF diameters:

vein lumen diameter should be:
greater than 2.5mm at the site

venous, ABG diameters:

vein lumen diameters should be: greater than 4mm at the site

which arm is evaluated first?

non-dominant

scanning arterial, what is included:

direct imaging
b-mode is used to assess diameters of ulnar and radial arteries (measure at prox & dist)

also assess:
calcification
intimal thickness
stenosis
compliance

scanning venous, what is included (after arterial)

b-mode imaging of superficial veins
trans images
vein walls compressibility
diameter of veins (all length)

superficial veins documented on venous scanning

cephalic
basiliac
median cubital vein

vein walls should be compressible and free of:

thrombus
webbing
calcium

what is documented on venous scanning?

patency
depth
wall thickness
calcification
location of thrombus or fibrosis

contraindications of scanning pre fistulae

IV lines
open wounds
limited patient positioning
dressings

evaluation of hemodialysis includes:

auscultate/palpate for bruit or thrill
linear array transducer
sagittal and trans views

observe for: hemodialysis

stenosis
aneurysm
pseudo-aneurysm
peri-vessel fluid

evaluate color and spectral doppler: hemodialysis includes:

normal high velocity
low resistance flow patterns
focal flow changes associated with imaged abnormality
flow outside of vessel

how is volume flow calculated?

using instrument software
volume flow through the vessel is calculated using a time-averaged mean velocity and the diameter of the vessel to calculate the cross sectional area

TAMV

time average mean velocity

flow volume equation

Q= graft area x TAV x 60 seconds

TAV

time average velocity
the measurement of the instantaneous average for mean velocity over time

cm/sec

most common site of stenosis is:

venous anastomosis & outflow vein

response of venous anastomosis & outflow vein when stenosed:

typically a hyperplasia response to high flow rate/increased shear stress as well as trauma

normal interpretation:

high velocity
low resistance waveform

abnormal interpretation:

high resistance waveform
outflow abnormality
OR
decreased systolic upstroke
dampened waveform
low velocities
inflow disease

(general velocity criteria : > 50% stenosis )at the anastomosis values are: PSV

> or equal to 400 cm/sec

at the anastomosis values are: velocity ratio

> 3

at the anastomosis values _________ defects are present

intraluminal

(general criteria for > 50% stenosis) along the venous outflow: PSV

> or equal to 300 cm/sec

along the venous outflow: velocity ratio

> 2

along the venous outflow, velocities ______ 50 cm/sec

<

accepted value for the access over time:

> 800 ml/min

value that is suggestive of a failing access at the access is:

< 500 ml/min

extravascular mass

anechoic mass with no flow

extravascular mass includes

seroma
hematoma
thrombosed pseudoaneurysm

pseudoaneurysm is:

active blood flow outside the vessel

(yin-yang sign)

treatment for pseudoaneurysm

surveillance
open surgical repair
endovascular stent graft exclusion
size of the neck/defect precludes thrombin injection

what is a steal

large blood volume moving through the fistulae that does not perfuse the body and therefore may impact cardiac function

steal syndrome is:

arterial blood flow distal to the fistula is reversed
flowing into the venous circulation may result in hand ischemic pain

assessment of steal syndrome

duplex to document retrograde flow in the artery distal to the fistula
obtain PPG tracing on multiple digits

what is the preferred method to assess steal syndrome

PPG tracing

if no change in PPG tracing?

no steal

if there is a change in PPG tracing?

there is a steal

what has better patency?

fistula

what is the most common site of stenosis or occlusion of a hemodialysis graft?

outflow vein

____ peak systolic velocities with _____ resistance waveform may indicate?

low peak systolic velocities;
low resistance;

= inflow artery stenosis