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264
Chapter 4 · Arteriovenous Fistulas
4.1 Clinical Role ofArteriovenous
Fistula Evaluation
4.1.1 Background
Of the 50,000 patients with end-stage renal failure in Germany,
each year some 15,000 become candidates for creation of a
4
hemodialysis access. A native arteriovenous (AV) stula has a
better prognosis with longer patency and fewer complications
such as infections and is preferred to a synthetic gra (Tordoir
etal. 2007). An advantage of a synthetic dialysis access is that
it can be used earlier, while a native stula needs time to
mature before it can be used for hemodialysis. A synthetic
shunt is the second option in patients whose native vein (typ-
. Table4.1 Types of arteriovenous (AV) stulas
Type of stula Description
Congenital AV
stula
Acquired AV
stula
Therapeutic
AV stula
Direct anatomic connection between the
arterial and venous system or indirect
communication through short circuits in the
soft tissue
Iatrogenic: complication of arterial catheter
examinations or renal transplant biopsy
Trauma
Spontaneous
Temporary: after thrombectomy for pelvic
vein thrombosis
ically the cephalic vein) is deemed unsuitable because of a
small lumen or because it has undergone thrombotic or
brotic degeneration as a result of frequent puncture. A mini-
Permanent: for hemodialysis access in renal
failure
mum ow volume is necessary to ensure adequate dialysis
treatment. Protocols in the USA require a ow volume of at
least 350mL/min, while smaller volumes of 200–300mL/min
are still considered acceptable in some European countries
including Germany. is requirement informs the preoperative search for a suitable vein for creating an AV stula and
the identication of patients who need a synthetic vascular
access. Preoperative vascular mapping contributes important
information for selecting the most suitable hemodialysis
access for each patient.
stulas. Such stulas have no hemodynamic eects and
are not apparent on color duplex ultrasound.
5 In Parkes Weber syndrome, larger AV stulas are present
(and may be the cause of excessive growth of the aected
limb). e feeding arteries and draining veins of these
larger stulas are detectable by duplex ultrasound, which
thus allows dierentiation of Parkes Weber syndrome
from Klippel-Trenaunay syndrome (
. Fig.4.2).
5 Servelle-Martorell syndrome is characterized by relative
undergrowth of the aected limb (typically the arm).
4.1.2 Diagnostic Evaluation ofPatients
withAbnormal andSurgically
Created Fistulas
e predominant vascular abnormalities are multiple
hemangiomas and varicose veins. Demonstration of
varicosis by duplex ultrasound may become relevant in
the dierential diagnosis.
An AV stula is a direct communication between an artery
and a vein that bypasses the capillary bed. Clinically, a stula
is recognized by a palpable thrill and a more or less persistent
high-frequency bruit that is present throughout the cardiac
cycle and varies with stula ow.
Acquired stulas usually develop aer trauma or iatrogenic
vascular injury during invasive procedures such as catheter
examinations (. Table4.1).
e third type are therapeutic stulas, which are pre-
dominantly created for hemodialysis access. erapeutic AV
4.1.2.1 Types ofAV Fistulas
Congenital, acquired, and therapeutic AV stulas are distinguished.
A congenital AV stula can occur in the form of a direct
anatomic connection between the arterial and venous system
(malformation), the presence of a blood-conducting struc-
stulas are temporary or permanent and include:
5 Temporary AV stula aer thrombectomy for pelvic vein
thrombosis
5 Fistula to improve patency in patients with a femorocru-
ral bypass gra and poor runo (controversial)
5 AV stula for hemodialysis access.
ture between an artery and a vein (such as an aneurysm), or
multiple short circuits in the so tissue or bone. Congenital
stulas can be part of complex angiodysplastic syndromes. In
most patients with an angiodysplastic syndrome, the combination of clinical symptoms usually allows the diagnosis to
be made:
5 Klippel-Trenaunay syndrome is characterized by
unilateral limb hypertrophy with the aected limb
showing nevus ammeus and venous anomalies
4.1.2.2 Creation ofaHemodialysis Access
An AV stula established for hemodialysis access must:
5 have the right size to ensure a minimum ow volume for
adequate hemodialysis without inducing arterial steal or
cardiac insuciency,
5 have a long enough segment for puncture, and
5 be established at a site that causes the least patient
discomfort.
(atypical varicosis and phlebectasia). Sonographically,
the dysplastic venous changes are seen as convolutes of
varicose veins. AV stulas, if present, tend to be micro-
e wrist or the bend of the elbow is the best site for a hemodialysis access, both in terms of surgical technique and ease
b
4.1 · Clinical Role ofArteriovenous Fistula Evaluation
a
Lateral antebrachial cutaneous nerve
Median antebrachial vein
. Fig.4.1 a Distal cephalic vein stula in the forearm: side-to-end
anastomosis of the radial artery and distal cephalic vein. b Vascular access
created with a synthetic conduit: bridge graft connecting the brachial
artery and distal cephalic vein (From Heberer and van Dongen 1993)
Superficial branch
Radial artery
Median nerve
of radial nerve
of access. A minimum stula ow volume of 300mL/min is
required for dialysis, while a volume exceeding 15–20% of
the cardiac output may lead to cardiac insuciency.
In patients with no adequate vein for creating a direct AV
connection, a synthetic gra (polytetrauoroethylene/PTFE
or Gore-Tex) may be interposed.
e classic AV connection for hemodialysis is the BresciaCimino stula, which is an end-to-side anastomosis between
the cephalic vein and radial artery at the level of the wrist
(. Fig.4.1a) or between the cephalic vein and brachial artery
in the bend of the elbow. Synthetic accesses are established as
loops from the brachial artery at the elbow to the basilic or
brachial vein, most commonly as a U-shaped loop implanted
subcutaneously in the lower arm. Alternatively, a vascular
access can be established with interposition of a straight gra
between the brachial artery and the cephalic, axillary, or
jugular vein (
. Fig.4.1b).
e standard diameter of a PTFE prosthesis is 5 or 6mm.
It can be used for hemodialysis immediately aer implantation. A direct AV stula, on the other hand, requires
3–4weeks to mature before the vein carries enough blood
and can be punctured.
Natural AV stulas have a better prognosis than synthetic
accesses, which may be aected by various functional problems requiring repeat revision.
Both the unphysiologically high ow rates and repeat
puncture of the access vein induce intimal proliferation, frequently leading to stenosis and occlusion. Published vascular
access patency rates
range widely, depending on the patient
population, inclusion criteria, and type of access investigated.
e patency rate reported for Brescia-Cimino stulas is
265
80–90% aer 1year, 63–87% aer 2years, and approx. 65%
aer 4 years (Ahmad et al. 1998; Brittinger et al. 1966;
Harnoss etal. 1991; Keller etal. 1991, 1988). In contrast, synthetic gras have patency rates of 62–90% aer 1 year,
50–79% aer 2years, and approx. 40% aer 4years (Haimov
etal. 1979; Munda etal. 1983; Tellis etal. 1979). Good vascular access function is essential for the quality of life of patients
on chronic hemodialysis. To maintain access patency, it is
important to ensure timely recognition and proper interpretation of access-related problems. Noninvasive modalities
such as color duplex ultrasound are the most suitable diagnostic tests, enabling early identication of the underlying
cause of a reduced ow rate through the stula or other complications and prompt initiation of adequate therapeutic
measures.
4.1.2.3 Indications forColor
Duplex Ultrasound
Color duplex ultrasound is used in patients with congenital
or acquired AV stulas and patients with a hemodialysis
access. e indications include:
5 Congenital or acquired nontherapeutic AV stula:
5 Fistula detection
5 Localization
5 Identication of the feeding artery and draining vein
5 Estimation of stula ow volume
5 erapeutic AV stula:
5 Estimation of access ow volume
5 Evaluation of vascular access complications (with
search for underlying causes):
Ȥ Fistula ow too low for hemodialysis
Ȥ Peripheral ischemia (hand)/dialysis access steal
syndrome (DASS)
Ȥ Arm swelling
Ȥ Fistula occlusion
Ȥ Stenosis (at site of anastomosis or within the stula)
Ȥ Stenosis of upstream artery or draining vein,
peripheral ischemia (arterial steal) due to high
stula ow, and follow-up of outcome aer banding
Ȥ Puncture aneurysm
Ȥ Perivascular complications: abscess, hematoma
On color duplex ultrasound, a congenital or acquired (nontherapeutic) AV stula is characterized by a color Doppler
bruit (mosaic of colors) resulting from highly turbulent ow
in the stula and perivascular vibration. Moreover, the higher
ow velocity will cause aliasing if the scan parameters are set
for depicting normal venous ow.
e Doppler waveform from the feeding artery shows a
monophasic ow prole with a large diastolic component,
which is due to lower peripheral resistance. e draining vein
has an arterialized ow prole with severe turbulence.
e (color) duplex examination allows identication and
evaluation of the feeding artery and draining vein.
In patients with an AV stula for hemodialysis access,
ultrasonography enables noninvasive evaluation of access
complications and estimation of stula ow. Measurement of
4
266
Chapter 4 · Arteriovenous Fistulas
blood ow velocity in the feeding artery has been found to be
the most reliable method for determining stula ow volume, as measurement within the stula or draining vein is
degraded by turbulence and variability of stula diameter.
e measurement in the feeding artery upstream of the
venous anastomosis is used to calculate the stula ow volume by comparing it with the contralateral side or by subtracting blood ow in the artery distal to the stula. e ow
4
volume is calculated from the time-averaged mean velocity
and the cross-sectional area of the vessel.
ducer frequency must be adjusted to the required scanning
depth. e high ow velocities in a stula and the occurrence
of perivascular vibration artifacts make it necessary to use a
high pulse repetition frequency (PRF).
e choice of transducer, patient positioning, and the
procedure depend on the body region in which the stula is
clinically suspected (e.g., palpable thrill or limb swelling due
to disturbed venous drainage). Perivascular tissue vibration
or color bruit is a helpful artifact in color Doppler. It is caused
by fast or turbulent ow and can guide the examiner to the
site of the abnormal arteriovenous communication.
In spectral Doppler evaluation, the feeding artery is iden-
4.2 Examination Protocol, Technique,
andDiagnostic Role
tied by an abnormal, monophasic waveform with a larger
diastolic component due to low-resistance ow. Distal to the
stula, the normal triphasic ow prole that characterizes
4.2.1 Congenital andAcquired Fistulas
high-resistance ow in peripheral arteries is seen (. Fig.4.2d).
With this in mind, the examiner can identify a large AV
Accurate information on the site of a stula with its feeding
artery and draining vein is helpful for planning the surgical
procedure.
When a stula is suspected on clinical grounds, this
information serves to guide the sonographic search (in the
color duplex mode) for the abnormal arteriovenous communication, the inow artery, and the draining vein. e trans-
stula with hemodynamically relevant ow by intermittent
spectral Doppler interrogation of the artery above and below
the site of the suspected arteriovenous communication. e
point of transition from monophasic to triphasic ow is
where the stula is located. At the same time, venous return
proximal to this point will show pulsatile variation. In addition to precise localization, which is relevant when surgical
a
Common femoral
vein
AV fistula between
profunda femoris
artery and femoral vein
b
. Fig.4.2 a–c Congenital arteriovenous (AV) stula. Complex angiodysplasia with a cluster of entangled vessels just distal to the wrist. a In the
B-mode image (left), the vessels are seen as irregular hypoechoic areas. The color ow image (right) depicts ow signals in an AV macrostula,
where ow is fast enough to be detectable. The Doppler waveform from the feeding artery arising from the radial artery is monophasic with a
large diastolic component, which is characteristic of arteries feeding an AV stula. The arrow indicates the interdigital artery. b The Doppler waveform from the cephalic vein draining the stula shows pulsatile ow. c Angiogram showing the cluster of arteriovenous stulas. d A iatrogenic
AV stula commonly develops between the proximal profunda femoris artery and the femoral vein, typically when the puncture is made too far
peripherally. The diagrams show the Doppler waveform changes proximal to an AV stula (common femoral artery, monophasic pattern) and
distal to an AV stula (supercial femoral and profunda femoris arteries, both triphasic). The Doppler waveform from the draining vein proximal to
the AV stula shows pulsatile ow (common femoral vein). The magnitude of the diastolic ow component proximal to the AV stula reects the
ow volume within the stula (see . Fig.4.8 (Atlas))
d
Superficial femoral artery
Common femoral
artery
Profunda
femoris
artery
c
c
4.2 · Examination Protocol, Technique, andDiagnostic Role
revision is contemplated, the stula ow volume may have to
be calculated as well. is is done on the basis of the diameter
of the feeding artery, determined from the B-mode image,
and time-averaged ow velocity (angle-adjusted Doppler
measurement), from which the normal blood ow volume of
the artery is subtracted. e normal ow volume is determined in the artery of the same name on the contralateral
side. Veins draining a stula are characterized by an arterialized, though oen less pulsatile, ow prole.
4.2.2 Hemodialysis AV Fistula
267
a
6
4
4
4
In the sonographic evaluation of therapeutic AV stulas and
their clinical complications, it is not the morphologic or
hemodynamic changes as such that are crucial for deciding
about the therapeutic consequences, but rather the clinical
manifestations they produce. e indication for treatment is
chiey established on the basis of the clinical problems, while
the choice of treatment is made on the basis of duplex ultrasound or the results of other imaging modalities (PTA of the
existing AV stula, creation of a new dialysis access, revision,
ligation of collateral veins, aneurysm resection, banding, stula closure).
ere is an ongoing controversy about the benet of reg-
ular ultrasound follow-up of hemodialysis access stulas (see
7 Sect. 4.8.2). In general, routine sonographic surveillance is
not necessary, while clinical complications and low stula
ow should prompt a timely ultrasound examination to
identify the underlying cause. e clinical problems
determine the extent of the sonographic examination. In
patients presenting with signs of peripheral ischemia or cardiac insuciency, for instance, it is necessary to quantify the
stula ow volume. If dialysis ow has become insucient,
the examiner must look for stenosis of the feeding artery or
draining vein.
A forearm fistula is best examined in the sitting patient
with the elbow slightly bent and the forearm resting on a
support. e supercial course of the arm vessels enables
their examination with a high-frequency transducer (7.5–
10MHz). Use of a linear-array transducer has the advantage of providing better contact with the arm. An
arm
stula is examined in the supine patient with the arm
upper
comfortably positioned on a support for optimal exposure
of the stula site for transducer maneuvers. A high PRF is
necessary to capture the fast blood ow through the stula,
whereas the gain must be downregulated to eliminate
vibration artifacts. A lower PRF is necessary to depict slow
postocclusive ow. First, the examiner evaluates the stula
in transverse orientation, followed by hemodynamic evaluation in the longitudinal plane with spectral Doppler
interrogation of the feeding artery, the access vein or the
synthetic gra, and the draining vein. When required,
spectral Doppler imaging should include the anastomotic
sites.
3
5
2
b
6
2
. Fig.4.3a–c Diagram of the morphologic changes that can occur in a
hemodialysis access: a shortly after creation of the AV stula; b dilatation;
c stenosis (1 feeding artery, 2 artery supplying hand distal to access vein,
3 access vein, 4 dilatation and stricture due to scar formation at site of
frequent venipuncture, 5 stenosis due to kinking, 6 accessory vein arising
from access vein) (From Scholz 1998)
3
1
1
4
e spectral Doppler ndings from these sites, in conjunction with the patient’s clinical symptoms, guide the
further examination to identify the underlying pathology.
In the feeding artery, the indirect stenosis criteria
. Fig.4.12 (Atlas)) can be used when the Doppler wave-
(
form is obtained while the access stula is being compressed
to induce high- resistance ow as in a peripheral artery. In
inconclusive cases, arterial inow must be scanned continuously from the subclavian artery to the brachial or radial
artery in the longitudinal plane including spectral Doppler
sampling.
In patients with a Brescia-Cimino stula, the access vein
and draining veins are evaluated for dilatation or narrowing
(
. Fig.4.3).
e veins must be examined with very light pressure to
avoid compression, which may be misdiagnosed as stenosis.
is is achieved by placing several ngers or the edge of the
hand holding the transducer on the arm outside the course of
the stula. e transducer can thus be moved with very subtle pressure. Alternatively, undue pressure can be avoided by
placing the transducer somewhat lateral to the apex of the
268
Chapter 4 · Arteriovenous Fistulas
. Table4.2 Structured duplex ultrasound examination of patients with hemodialysis access problems (three-point strategy)
Site of spectral Doppler
interrogation
Feeding artery proximal to
venous anastomosis without and
with manual stula compression
4
Feeding artery distal to venous
anastomosis without and with
manual stula compression
Access vein 2–4cm from
anastomosis
vein wall and then tilting it to interrogate the vein. Synthetic
gras are less susceptible to compression.
Apart from palpation, the course of an AV stula is most
easily tracked sonographically in transverse orientation.
Spectral Doppler measurement is performed in the longitudinal plane at sites suspicious for stenosis. Perivascular vibration artifacts, caused by fast ow, can be eliminated by slightly
compressing the area next to the transducer with the at
hand, while at the same time avoiding excessive compression
of the vein. Proper positioning is veried in the B-mode by
slightly changing the pressure exerted with the transducer.
Tortuous veins are better appreciated transversely. In patients
with an intricate stula, an overview of ow directions in the
dierent venous limbs can be obtained in the color duplex
mode.
When a narrowing is encountered in the B-mode examination or when aliasing or perivascular tissue vibration
(mosaic of colors) appears in the color duplex mode, a
Doppler waveform is obtained from that site in longitudinal
orientation to conrm stenosis and grade its severity.
While the focus is on vascular assessment, it is also
important to pay attention to perivascular structures in longitudinal and transverse planes (and color duplex as needed)
to dierentiate hematoma, abscess, and AV access aneurysm.
Diagnostic information Doppler waveform ndings (direct/indirect criteria)
(Central) arterial stenosis, proximal to
venous anastomosis
Fistula stenosis Increasing pulsatility (in proportion to stenosis
Dialysis access steal syndrome (DASS)
(symptomatic/asymptomatic)
Peripheral perfusion reserve PSV increase (quantitative) with stula compression
Anastomotic stenosis Intrastenotic PSV increase (stenosis grading)
Stenosis of access vein/partial thrombosis Increasing pulsatility (in proportion to stenosis severity)
Delayed upstroke, reduced pulsatility (during stula
compression)
severity); increased peripheral resistance
Reduced PSV, to-and-fro ow, and retrograde ow will
be seen in proportion to severity of arterial steal
for hemodynamic evaluation of dialysis access problems, the
author has developed a time-ecient protocol based on
spectral Doppler interrogation of three representative sites
(three-point strategy) (. Table4.2) for identication of common, treatable access-related problems.
First, the examiner identies the brachial artery in the
upper arm in transverse orientation and then obtains a waveform in the longitudinal plane. A monophasic waveform
with a large diastolic component conrms undisturbed ow
through the stula downstream of the sampling site. A waveform with more pulsatile ow or a triphasic waveform (characteristic of normal high-resistance ow in this artery)
indicates obstructed ow in the stula (occlusion or highgrade stenosis) or in the draining vein (axillary vein thrombosis). Spectral Doppler measurement at this site is then
repeated with manual compression of the AV stula. is
should result in a triphasic waveform with a steep systolic
upstroke (short acceleration time). Failure to obtain a highresistance triphasic waveform with absence of a whipping
sound during stula compression suggests an obstructive
lesion in the feeding artery upstream of the sampling site
(typically the subclavian artery). e examiner then continuously scans the artery up the arm to identify and grade the
stenosis.
e second site of spectral Doppler evaluation is the main
4.2.2.1 Time-Ecient Ultrasound Workup
ofHemodialysis Access Problems
Color-coded duplex ultrasound combines two sonographic
techniques that enable ecient diagnostic workup of hemodialysis access problems based on the patient’s clinical presentation. With gray-scale ultrasound, the examiner can
identify the course of the stula, detect morphologic abnormalities such as aneurysm or luminal narrowing due to scarring, and identify accessory veins diverting blood away from
the access vein.
e mainstay of the ultrasound examination is spectral
Doppler interrogation for evaluation of stula ow, arterial
perfusion, and stenosis grading. To exploit this unique tool
artery distal to the venous anastomosis. Again, Doppler
waveforms are obtained without and with compression of the
stula to assess the steal eect resulting from the hemodialysis access (the nger arteries may be included in the examination in patients with ischemia).
e third site of Doppler interrogation is the access vein
approx. 1–3 cm distal from the anastomosis, where stula
ow is assessed and anastomotic stenosis can be identied.
Additional components of the sonographic workup depend
on the spectral Doppler ndings at these three key sites in conjunction with the patient’s clinical symptoms or hemodialysis
access problem (inadequate ow volume for hemodialysis,
peripheral ischemia (ngers, hand), arm swelling).
4.4 · Fistula Maturation andFlow Volume Measurement
269
4
4.3 Doppler Waveform Changes
Characteristic ofAV Fistulas
e low peripheral resistance associated with an AV short
circuit results in continuous systolic and diastolic ow and a
large diastolic ow component in the feeding artery. is
altered ow situation gives rise to a number of specic sonographic ndings in patients with an AV stula:
5 Monophasic ow prole due to continuous systolic and
diastolic ow with a large diastolic component in the
feeding artery
5 Pulsatile ow in the arterialized draining vein
5 Very turbulent ow across the stula (along the length of
the access vein)
5 Perivascular tissue vibration around the stula
5 Dilatation of the inow artery and draining vein when a
hemodynamically relevant AV stula has been present
for many years.
A return to pulsatile ow in the feeding artery of a therapeutic AV stula indicates low stula ow due to obstructed
venous drainage, stula stenosis, or stula occlusion
(. Figs.4.15 and 4.18 (both Atlas)).
Perivascular tissue vibration around an AV stula, especially during systole, is a tissue motion artifact and may be
seen in color Doppler as extravascular color (color bruit). e
smaller the stula caliber and the larger the jet, the more pronounced the perivascular vibration artifact. Turbulent ow in
the stula is identied by a mix of colors and by considerable
spectral broadening in the Doppler waveform; there may
even be retrograde ow components during systole.
e outow vein is dilated and, due to arterialization,
ow is pulsatile and turbulent (resulting in spectral broadening, primarily close to the stula). Vessel wall and so tissue
vibration artifacts in the color duplex scan can be minimized
by slight manual throttling of arterial inow, which is especially important when performing spectral Doppler measurement for comparison of ow velocities upstream and
downstream of a suspected stenosis.
All draining veins have arterialized ow. Accessory
venous branches that divert blood away from the access vein,
but are unsuitable for hemodialysis, can thus be identied
and ligated.
e ow changes in a hemodialysis access that has been
used for many years may lead to intricate ow patterns in
arteries that are only indirectly, through collaterals, connected to the feeding arteries (e.g., steal phenomena, supply
of a radial artery stula by the palmar arch and ulnar artery).
Evaluation of color-coded blood ow directions allows correct interpretation and identication of shunt problems (such
as ischemia of the ngers and reduced ow) under such complex ow conditions as well.
e ow velocities derived from spectral Doppler ultrasound vary widely with stula age and dilatation. Peak systolic velocity (PSV) in the inow artery may be up to twice as
high as in the contralateral counterpart with a large diastolic
ow component, resulting in a Pourcelot resistance index of
0.7–0.4. Depending on the diameter, even greater variability
in ow velocities of 50–150cm/s may be seen in the arterialized draining vein. Flow velocity in a synthetic AV access
gra varies with arterial inow and venous outow resistance. Depending on the gra diameter, systolic velocities
range from 100 to 400cm/s with 60–200cm/s at end diastole
(Lockhart and Robbin 2001).
4.4 Fistula Maturation andFlow
Volume Measurement
A decreased ow through the access stula, due to complications such as stenosis, impairs hemodialysis function.
However, only a high-grade stula stenosis becomes functionally relevant, which, according to Kathrein etal. (1988, 1991),
is dened as a decrease in the volume ow rate below 250mL/
min. Although this would seem to be the most obvious thing
to do, blood ow is not measured directly in the aected
access vein. is is because abrupt changes in diameter, especially in older stulas, and changes in the lumen shape (elliptical) give rise to errors. Determination of mean velocity within
the stula is also impaired by turbulent ow (spectral broadening). For these reasons, the
alysis access can be estimated most reliably by determining
time- averaged mean ow velocity in the main feeding
artery
(typically the brachial artery). Flow volume measurements performed on dierent ultrasound machines may vary
by up to 30%. One reason is the use of dierent methods for
determining the cross-sectional area (direct planimetric measurement or calculation from diameter, leading-edge method).
Another is the way in which ow velocity is determined: it
may be calculated as the mean velocity across the vessel lumen
or as the median velocity. Inadequate receive gain can thus
produce measurement errors. Calibration measurements are
rarely done before ow volumes are measured. e discrepancies are less relevant as long as serial measurements are performed with the same equipment.
Grosser et al. (1991) compared volume ow measurements performed in the brachial artery, radial artery, and
stula vein and found
ments in the brachial artery
eects, the calculation of the cross-sectional area is prone to
errors, and the error is larger in smaller vessels such as the
radial artery (. Fig. 1.28). is is because the error in measuring the vessel diameter is potentiated in the calculated
ow volume (because the radius is squared in calculating the
cross-sectional area).
Direct ow measurement in the access vein is oen unreliable due to the wide luminal variability of Brescia-Cimino
stulas, the oval shape of the cross-sectional area, and turbulent ow, which rarely allows valid determination of mean
ow velocity.
ow volume in an AV hemodi-
the best reproducibility for measure-
. However, due to blooming
270
Chapter 4 · Arteriovenous Fistulas
erefore, in patients without any apparent perfusion
abnormalities in the arms, bilateral ow measurement has
emerged as the more valid method. is is best done in the
brachial artery in the mid upper arm, where a good insonation
window allows adequate measurement. In patients with adequate, high stula ow, residual brachial artery contribution
to arm perfusion is negligible.
An even more reliable method has been developed by the
4
author and involves two measurements of blood ow velocity
in the brachial artery upstream of the arteriovenous anastomosis– one without and one with short manual compression
of the stula. e stula ow volume is then calculated as the
ow volume without compression minus the volume with
compression of the stula (. Fig. 4.10e–g). In the author’s
experience, this method is simple and reliable. It is only limited in individuals with older synthetic loops and in individuals with large arms.
Volume ow is calculated (see 7 Sect. 1.1.2.4) by multiplying the cross-sectional area (determined in the B-mode) with
the time-averaged mean blood ow velocity (derived from
spectral Doppler measurement with an acute angle <50°).
is is done automatically when this feature is included in the
calculation package. Accurate calculation of the crosssectional area of the brachial artery is ensured by measuring
the diameter using the leading-edge method (to minimize
errors due to the blooming eect occurring in gray-scale
ultrasound at interfaces of high acoustic impedance such as
the vessel wall;
rial diameter through the cardiac cycle into account. To this
end, the systolic and diastolic diameters are weighted at a ratio
of 1:2in the equation for cross-sectional area calculation.
Direct determination of ow volume in the access vein
is discouraged
been used for a long time. However, when there is complex
branching of veins, an attempt can be made to determine the
functionally relevant proportion of blood ow through the
access vein. To do so, the Doppler sample volume must be
placed in a straight segment of the vein with little turbulence
and without major caliber variation.
e volume ow rate can also be determined to assess
maturity of a newly created hemodialysis access before rst
use or when maturation appears to be delayed (e.g., low
ow). A wide range of volume ow rates from 500 to
1200mL/min make an AV stula suitable for hemodialysis.
e predictive value of several ultrasound criteria such as
minimum venous diameter for hemodialysis AV stula maturation was investigated in a retrospective study of 69
patients (Robbin etal. 2002). Fistula adequacy for hemodialysis was 89% in patients with a minimum venous diameter
of 4mm versus 44% for diameters of less than 4mm. A ow
volume of 500mL/min or greater enabled adequate hemodialysis in 84% of cases versus only 43% if ow volume was less
than 500 mL/min. Failure of a stula to mature should
prompt a color duplex ultrasound examination to search for
stenosis, focusing on the inow artery and the anastomosis.
Venous outow obstruction is more likely to induce the formation of a collateral pathway circumventing the access vein,
. Fig. 1.28) and by taking the variation in arte-
, especially when a hemodialysis access has
which may cause arm swelling. When too much blood is
diverted away from the main vein, the latter may be unsuitable for hemodialysis. Arterial or venous stenosis can be
treated by PTA and followed up by serial ultrasonography;
however, long-term patency is poor (Clark etal. 2007). An
anastomotic stenosis requires surgical revision. Low stula
ow increases the risk of occlusion, which is over 50% when
the ow volume drops below 300 mL/min (Lockhart and
Robbin 2001; Bay etal. 1998).
4.5 Documentation
e documentation of the ultrasound ndings depends on
the clinical indication for the examination and the underlying cause of the hemodialysis access complication. Individual
images oen give only a poor representation of the intricate
vascular patterns that may be encountered, especially in
hemodialysis patients who have undergone repeat revision of
their access. To facilitate serial examinations of hemodialysis
access stulas, images and waveforms from the following
sites should be documented routinely:
5 A longitudinal view and Doppler waveform from the
feeding artery
5 A longitudinal view and Doppler waveform from the
anastomosis
5 A longitudinal view with Doppler waveform from the
access vein
5 A Doppler waveform from the artery distal to the
anastomosis
e documentation of pathology depends on the ndings
(e.g., stenosis including grading) and the clinical presentation. Prior to surgical revision, all vessel segments involved
must be assessed and the ndings documented, for example,
the axillary or jugular vein if creation of a synthetic gra
access is planned. A drawing of the vascular anatomy around
the hemodialysis access stula may be helpful to document
complex vascular relationships for subsequent follow-up
examinations, to report the ndings to colleagues, and to
document the sites of measurement (e.g., blood ow velocity
without/with stula compression).
4.6 Vascular Mapping Prior
toAV Fistula Creation
Creation of a direct, native arteriovenous stula for hemodialysis access is always preferable to a synthetic gra. e site
should be as distal as possible to minimize ischemic complications and to avoid excessively high ow volumes. Note,
though, that a Brescia-Cimino stula connecting the radial
artery and cephalic vein in the forearm has an early failure
rate of 15.3% and a 1-year patency rate of only 62.5%
(Rooijens etal. 2004). e risk of failure and early occlusion
can be lowered by performing preoperative vascular mapping, especially if the creation of a forearm stula is planned.
4.7 · Hemodialysis Access Complications
271
4
. Table4.3 Predictors of adequate AV stula ow and good
hemodialysis access function in preoperative color duplex and
spectral Doppler mapping
Preoperative color
duplex
Arterial inow >50cm/s Triphasic waveform
Arterial diameter >2.0mm –
Venous outow – Venous ow with
Venous diameter
(possibly with
placement of a
tourniquet)
Minimum Doppler waveform
respiratory phasicity
and, toward the center,
cardiac pulsatility
>2.5mm –
In most cases, a careful preoperative clinical evaluation will
identify the most suitable type of hemodialysis access for the
patient (. Table 4.3); however, preoperative color duplex
imaging has been shown to facilitate the decision and
improve the patency rate (Silva etal. 1998; Huber etal. 2002).
e radial artery diameter should be at least 2–2.5 mm
(Korten etal. 2007); a diameter of <1.5mm was found to be
associated with low ow volumes and an early occlusion rate
of up to 45% (Parmar et al. 2007). An atherosclerotic vein
may be unsuitable and fail to undergo adequate dilatation.
e cephalic vein should be >2.5mm in diameter to ensure
adequate venous drainage. A cephalic vein diameter<2mm
was reported to result in inadequate stula maturation in
24% of cases (Mendes etal. 2002). A tourniquet can be placed
to estimate the diameter of the vein with maximum lling
(Lockhart etal. 2004). e validity of preoperative diameter
measurement for predicting AV stula maturation is conrmed by high intra- and interobserver agreement (Planken
etal. 2006). Preoperative color duplex mapping should rule
out ow obstruction or sclerosis of the cephalic vein, which
may have developed as a result of thrombosis from repeat
prior cannulation. Spectral Doppler interrogation should be
performed to conrm unobstructed central venous drainage
through the axillary vein, seen as normal respiratory phasicity and transmitted pulsatility from the heart.
For ease of cannulation, a supercial vein is preferred for
creation of a hemodialysis stula. Ideally, the candidate vein
should not be more than 0.5cm from the skin surface. If such a
vein is not available, e.g., in patients with large arms, the creation
of a hemodialysis access may involve mobilization and supercial tunneling of the vein or placement of a synthetic loop.
problem or stula ow becomes inadequate for dialysis, this
should prompt timely workup by color duplex ultrasound.
Signs of obstructed venous drainage include edema, swelling
of the arm, livid discoloration, prolonged bleeding aer
removal of the dialysis needles, and increased venous pressure during dialysis. An arterial problem is suggested if there
is ischemia with pain and necrosis of the stula hand (arterial
steal) or inadequate ow during dialysis.
Poor stula ow with inadequate dialysis has many
causes. Duplex ultrasound is an excellent tool for workup
and identifying the underlying abnormality. e problems
include:
5 Decreased inow due to stenosis or occlusion of the
feeding arteries
5 Decreased drainage due to obstruction of outow veins
(thrombus, stenosis)
5 Cardiac insuciency
5 Insucient blood ow in the access segment due to
diversion of blood into venous branches
5 AV stula thrombosis with reduction of patent lumen
5 Anastomotic stenosis
In addition, the function and prognosis of a dialysis stula
can be impaired by the following conditions and problems:
5 Aneurysm (true or false)
5 Local infection, hematoma
5 Dicult cannulation due to deep or small vessels
Other hemodialysis access complications are peripheral ischemia (hands, ngers) and arm swelling.
4.7.1 Hemodialysis Access Stenosis
4.7.1.1 Causes ofHemodialysis
Access Stenosis
Hemodialysis access stenosis is most commonly caused by
neointimal hyperplasia, scarring at puncture sites, and dissection. Intimal proliferation begins 4–8weeks aer creation
of the AV stula, and progression varies widely among individuals. e factors promoting intimal proliferation in an AV
stula include turbulent ow at the anastomosis, intimal
damage during cannulation, and increased venous pressure
due to high ow rate. e resulting higher shear stress causes
chronic damage, triggering repair processes with stimulation
of vascular smooth muscle cells. Constriction due to neointimal proliferation tends to occur at valve sites. Finally, the
unphysiologically high venous return through the hemodialysis access may be obstructed in the narrow costoclavicular
space, which, under normal conditions, presents no clinically
relevant ow obstacle.
4.7 Hemodialysis Access Complications
Maintenance of good AV stula function without complications (arm swelling, peripheral ischemia) is essential for
patients on hemodialysis. If clinical evaluation identies a
4.7.1.2 Stenosis Detection andGrading
e clinical presentation and palpation ndings as well as
problems encountered during hemodialysis (needle clinging– insucient inow; increased venous pressure– outow obstruction) guide the ultrasound examination. Based
272
Chapter 4 · Arteriovenous Fistulas
. Table 4.4 Criteria for identifying relevant hemodialysis
access stenosis (Modied from Tordoir etal. 1989; Kathrein 1991;
Grosser etal. 1991)
Direct criteria Indirect criteria
Luminal narrowing (B-mode):
diameter<2mm indicates
4
high-grade stenosis requiring
treatment
cutos:
– Arterial inow: >2.0
– Access vein: >3.0 (treatment
required for >4–8)
– Arteriovenous anastomosis: >3.0
Reduced stula ow
volume (<300mL)
Prestenotic waveform:
return to high-resistance
ow (triphasic)Peak systolic velocity (PSV) ratio
Poststenotic waveform:
delayed systolic upstroke
was found to have 91% sensitivity and 97% specicity for stenosis detection in a failing hemodialysis access stula (Doelman etal. 2005).
Stenosis of an AV stula (e.g., Brescia-Cimino) most commonly aects the anastomosis (55–75%) (Kathrein 1991; Pietura etal. 2005) and the access vein (25%) (Turmel- Rodrigues
etal. 2000) (. Fig.4.4). In older AV stulas, stenotic narrowing
may be seen upstream and downstream of dilated segments or
occur as a result of scar formation at sites of frequent puncture.
Here, a residual lumen <2mm on B-mode imaging can serve
as a predictor of imminent access failure. Otherwise, hemodynamic stenosis grading is more reliable, with ow velocities
>300cm/s suggesting hemodynamically relevant stenosis.
While normal peripheral arteries have high-resistance ow
with a triphasic waveform, an artery feeding a hemodynamic
access has low-resistance ow with a monophasic waveform.
Compared with the gold standard, DSA, duplex ultrasound
on these clues, the site of the suspected obstruction is evaluated with color duplex imaging and spectral Doppler
interrogation using basically the same criteria as for identication of peripheral artery stenosis in patients without an
AV stula. Direct criteria include local ow acceleration,
turbulent ow, and perivascular vibration artifacts. Changes
in the ow prole (prestenotic versus poststenotic) are of
limited value as monophasic ow predominates due to the
low resistance resulting from the venous short circuit. Still,
a high-grade obstruction will induce increased upstream
pulsatility and decreased downstream pulsatility. With a
high-resolution transducer, obstructions can be identied
in the B-mode. eir hemodynamic signicance is then
evaluated by spectral Doppler measurement. Moreover, the
B-mode information enables dierentiation of intramural
and extramural causes of luminal narrowing. An example
of an intramural process is intimal proliferation. Other
steno-occlusive lesions are local thrombotic deposits. ese
can be dierentiated from extramural structures such as
hematomas. Early intimal proliferation is seen as a
hypoechoic wall deposit or a color lling defect. With further progression, the proliferating intima becomes inhomogeneous and may calcify.
Because normal ow velocity is higher in an AV stula
and the feeding artery, a higher peak systolic velocity (PSV)
of 2.5m/s should be used as a cuto to identify hemodynamically signicant stenosis. Note, though, that most moderate
stenoses identied using this higher cuto do not require
treatment unless a patient develops hemodialysis access dysfunction or other complications. Moreover, a doubling of the
PSV compared with the prestenotic PSV can serve as a criterion for stenosis in a recently established stula, but, due to
caliber irregularities, is unreliable in older, dilated stulas.
Indirect signs of hemodialysis access stenosis include a return
to a triphasic ow prole in the feeding artery and a drop of
the stula ow volume below 250mL/min (. Table4.4).
Current clinical practice guidelines recommend duplex
ultrasound for quantication of hemodynamically relevant stenosis
(National Kidney Foundation 2006).
erefore, as noted above, the indirect criterion of a change
from triphasic to monophasic ow cannot be used for stenosis
detection unless the waveform is obtained during short manual compression of the AV stula. With compression, ow
should become triphasic, as in a normal native peripheral
artery, while persistent monophasic ow indicates stenosis.
e altered hemodynamic situation in and around a hemodialysis access also requires some adjustment of the blood ow
velocity cutos (absolute values and ratios) identied for stenosis grading in native arteries. Caution is in order when absolute PSV is used because it is aected not only by the known
systemic factors such as blood pressure but also by other factors, most notably the stula ow volume. e eect of the
latter is notoriously dicult to quantify. Parameters expressing
the stenosis-related increase in blood ow velocity in relation
to ow velocity outside the stenosis, e.g., 2cm upstream, are
considered more reliable measures of stenosis severity. In general, it is assumed that a stenosis begins to become hemodynamically relevant when there is doubling of ow velocity or
50% cross-sectional area reduction. is is expressed by a PSV
ratio of 2 (intrastenotic PSV divided by prestenotic PSV). In
patients with a hemodialysis access, the PSV ratio can also be
used to grade stenosis of the venous anastomosis.
As noted, the use of absolute PSV thresholds alone ignores
the considerable hemodynamic variability that may be encountered in an articially created stula and may lead to falsepositive results. Nevertheless, absolute PSV cutos of 2.5ms
were used in scientic studies (Kathrein 1991; Grosser etal.
1991; Tordoir etal. 1989). As long as adequate hemodialysis is
ensured, ow velocities exceeding 2.5m/s are acceptable at the
anastomosis, and relative stenosis may even be desirable to
avoid excessively high stula ow with ischemia of the hand.
While a PSV ratio cuto of 2 is assumed to indicate 50%
stenosis in the feeding artery, most investigators use a higher
ratio of 3 to identify hemodynamically relevant stenosis in the
body of the stula (. Fig.4.4e, f). Even then, the hemodynamic
degree alone is no indicator of the therapeutic relevance of the
stenosis. In general, treatment is not required unless PSV
ratios of 4–8 are measured, and the decision is always made
4.7 · Hemodialysis Access Complications
273
abc
def
. Fig.4.4a–f Stenosis of hemodialysis access. a, b B-mode image (a) demonstrates stenosis at the venous anastomosis of a Brescia- Cimino s-
tula caused by a ap (arrow) in the access vein (which is seen closer to the transducer than the brachial artery). Peak systolic velocity (PSV) is 6m/s
(b), consistent with high-grade stenosis. The automatically calculated time-averaged mean velocity is 202.0cm/s (TAMEAN in the black inset in the
left upper corner in b). In the spectral display, mean velocities over time are represented by a green line. A ap as in this patient is often dicult
to evaluate by angiography, and the sonographic diameter criterion for therapeutically relevant access vein stenosis (<2mm in transverse plane)
does not apply here. c Use of indirect stenosis criteria in the workup of suspected stenosis: The waveform from the brachial artery does not show
the expected loss of pulsatility characterizing an artery feeding an AV stula. Instead, there is slightly pulsatile ow with a small diastolic component, indicating abnormally increased resistance to blood ow through the stula. d The waveform from the access vein distal to the anastomosis
shows poststenotic ow with a delayed systolic upstroke and slightly increased PSV.These ndings are consistent with an anastomic stenosis.
e, f Dierent patient presenting with high-grade AV stula stenosis with a PSV ratio of 6 (calculated from intrastenotic PSV of 437cm/s (f) and
prestenotic PSV of 71cm/s). The waveform was obtained by continuously moving the transducer across the skin (and includes the sites of prestenotic and intrastenotic PSV measurement). The stenosis is due to an intimal ap and external compression of the stula by a largely thrombosed,
puncture-induced pseudoaneurysm (the vessel wall leak is indicated by residual ow, encoded in blue, within the otherwise thrombosed aneurysm sac). Based on these ultrasound ndings, the treatment indicated is surgical revision, not PTA
4
taking additional parameters such pulsatility of ow in the
feeding artery and stula ow volume into account. e PSV
ratio is not reliable unless it can be determined in an access
vein segment with a relatively constant diameter. When there
is marked widening of the prestenotic segment, the diameter
should be used as an alternative diagnostic marker of stenosis.
Flow obstruction in the AV stula is suggested indirectly
by an increase in pulsatility in the feeding artery. High-grade
stenosis or occlusion of the AV stula can even restore the
triphasic ow prole characteristic of high-resistance ow in
native peripheral arteries. A triphasic waveform obtained in
the feeding artery or the vein near the venous anastomosis is
thus diagnostic of a relevant ow obstruction downstream of
the sampling site (
4.7.1.3 Proximal Feeding Artery Stenosis
. Fig.4.18 (Atlas)).
When no stenosis has been detected at the anastomosis or in
the access vein to explain decreased ow, the search must
continue proximally along the inow (subclavian and axillary
arteries). Feeding arteries become susceptible to atherosclerosis aer many years of hemodialysis. Since all vessels communicating with the stula have monophasic ow, a
monophasic ow prole cannot be used as a stenosis criterion
here. As noted before, the examiner can eliminate the stularelated modulation of ow in the feeding artery by manually
compressing the stula. During compression, the feeding
artery supplies only the arm and hand and the situation is the
same as in native peripheral arteries, meaning that both direct
and indirect criteria of stenosis apply (. Fig.4.12 (Atlas)).
4.7.2 Diagnostic Evaluation forSpecic
Hemodialysis Access Problems
e following subsections describe the diagnostic workup of
common complications in patients with a hemodialysis
access and discuss the therapeutic relevance of ultrasound
ndings in the management of these complications.
4.7.2.1 Peripheral Ischemia
An AV stula in the arm can lead to critical hypoperfusion of
the hand, in particular in patients with pre-existing peripheral
arterial occlusive disease (PAOD) or in diabetics with macroand microangiopathic medial sclerosis and stenotic lesions. In
addition to the blood drained through the low- resistance
stula, blood may be diverted from the arteries supplying the