DUPLEX ASSESSMENT
of
DIALYSIS ACCESS MATURATION
R. Eugene Zierler, M.D.
The D. E. Strandness, Jr. Vascular LaboratoryUniversity of Washington Medical Center
Division of Vascular SurgeryUniversity of Washington, School of Medicine
DISCLOSURE INFORMATION
No relevant
financial or commercial
relationships
R. Eugene Zierler, M.D.
Maturation process for an autogenous vein dialysis access
conduits involves 3 components:
1. Adequate diameter and length for cannulation
Diameter ≥6 mm
Usable length of ≥10 cm
2. Sufficient volume flow for effective dialysis
Calculated volume flow ≥600 mL/min
3. Superficial location that allows safe and repetitive puncture
Depth from skin surface <6 mm
Definition (Measurements)
ASSESSMENT OF ACCESS MATURATION
Anatomic and hemodynamic features of maturation can
be assessed by duplex scanning
Problems that interfere with maturation can be identified
Anastomotic stenosis or impaired arterial inflow
Large venous branches that divert flow
Narrowing of the venous conduit
Central venous outflow obstruction
Early intervention may permit salvage of conduits that
would not otherwise have matured
Role of Duplex Scanning
ASSESSMENT OF ACCESS MATURATION
Peak systolic velocity (PSV) is the main parameter used for
identifying arterial stenoses by duplex scanning (carotid,
renal, peripheral arteries)
Specific velocity threshold criteria are difficult to establish for
access conduits because of the wide variability in PSVs
High PSVs are common in well-functioning access sites
Maximum PSV and velocity ratio (Vr) have been used
B-mode and color-flow should be used to confirm stenoses
and intraluminal defects
Velocity Criteria for Access Conduit Stenosis
ASSESSMENT OF ACCESS MATURATION
Compared duplex PSV and Vr to angiographic % stenosis
780 autogenous access site stenoses in 281 patients
(47 brachiobasilic, 361 brachiocephalic, 372 radiocephalic)
≥50% stenosis in 740
<50% stenosis in 40
Velocity Criteria for Access Conduit Stenosis
Wo K, et al. Ann Vasc Surg 2017;38:99-104
PSV of ≥500 cm/s
showed best overall
sensitivity (89%) and
PPV (99%)
Vr was not reliable in
predicting stenosis
ASSESSMENT OF ACCESS MATURATION
The main hemodynamic requirement for successful dialysis is
a sufficient volume flow rate (minimum is 600 mL/min)
Functioning access sites typically have volume flow rates in the
range of 800 to 1200 mL/min (flow rates <500 mL/min are
generally predictive of impending access site failure)
Volume flow measurements are more predictive of overall
access site function than PSV
Even if there is evidence of a >50% stenosis, intervention may
not be necessary if the volume flow rate is adequate
Volume Flow
ASSESSMENT OF ACCESS MATURATION
Can be calculated based on velocity and vessel diameter
measurements obtained by duplex scanning
Q n A 60s n p(d2)/4 60s
Q Volume flow (mL/min)
n Time-averaged velocity across the vessel lumen (cm/s)
A Cross-sectional area of vessel at site of measurement (cm2)
d Lumen diameter (cm)
Volume Flow
ASSESSMENT OF ACCESS MATURATION
Assumptions
Circular cross-sectional area
Laminar (uniform) flow pattern
Unidirectional flow
Avoid
Non-circular vessels (flattened or irregular veins)
Turbulent flow (tortuous or kinked segments)
Inflow brachial artery is usually the best site
90% of brachial artery flow goes through the fistula
Experimental validation of duplex volume flow
measurements has shown an absolute error of 13% and a
high degree of correlation with timed blood collection
Volume Flow Measurement by Duplex
ASSESSMENT OF ACCESS MATURATION
Volume Flow Measurement by Duplex
Diameter measurement Doppler
sample volume
expanded to include the
entire lumen
Longitudinal (long-axis) View of VesselSpectral
waveform obtained at
Doppler angle of ≤60
Time-averaged velocity
obtained over at least 2 or 3 cardiac cycles
Mean velocity “tracker”
Calculation
ASSESSMENT OF ACCESS MATURATION
Volume Flow: Examples Good Diameter
Doppler angle
Sample volume
Mean tracker
Flow pattern
ASSESSMENT OF ACCESS MATURATION
Bad (sources of error)
Baseline noise
Mean tracker not working
Bi-directional flow
Brachial artery volume flow measurements are easier to obtain
and more consistent than access conduit measurements
UC San Diego reported a 2-part study on the use of brachial
artery volume flow in the assessment of access maturation
Part I: Studied the relationship between brachial artery volume
flow and access conduit volume flow in 75 patients
Hemodynamic data used to develop brachial artery flow
velocity criteria for predicting access site function
Clinical Application of Volume Flow
Ko SH, et al. J Vasc Surg. 2015;61(6):1521-1527
ASSESSMENT OF ACCESS MATURATION
Clinical Application of Volume Flow
Brachial Artery vs. Access ConduitVolume Flow Measurements
Brachial Artery PSV vs. Volume Flow
ASSESSMENT OF ACCESS MATURATION
Ko SH, et al. J Vasc Surg. 2015;61(6):1521-1527
Brachial Artery Velocities and Volume Flow Categories
Clinical Application of Volume Flow
LOW
<600 mL/min
ACCEPTABLE
600-800 mL/min
HIGH
>800 mL/min
PSV <100 cm/s PSV <150 cm/s PSV >150 cm/s
EDV/PSV* <0.2 EDV/PSV 0.2-0.4 EDV/PSV >0.4
Diameter >4.5 mm
ASSESSMENT OF ACCESS MATURATION
*EDV/PSV ratio is an indicator of outflow resistance, with higher values representing the low resistance expected in a normally functioning access site
Ko SH, et al. J Vasc Surg. 2015;61(6):1521-1527
Clinical Application of Volume Flow
Part II: Brachial artery velocities measured in 148 patients after
upper extremity dialysis access procedures
The estimated volume flow category was correlated with
access maturation and need for revision prior to first use
Access TypeLOW
<600 mL/min
ACCEPTABLE
600-800 mL/min
HIGH
>800 mL/min
Primary (n=86) 17 (19%) 32 (37%) 37 (43%)
Previously revised (n=62) 4 (6)% 8 (13%) 50 (81%)
Total (n=148) 21 (14%) 40 (27%) 87 (59%)
Subsequent Revision 15 (71%)* 4 (10%) 2 (2%)
ASSESSMENT OF ACCESS MATURATION
*P<.0001
Ko SH, et al. J Vasc Surg. 2015;61(6):1521-1527
Clinical Application of Volume Flow
Access maturation was confirmed when:
Brachial artery volume flow was >800 mL/min
Conduit imaging showed successful cannulation criteria
(conduit diameter ≥5 mm, depth <6 mm)
Brachial artery velocities indicating VF <600 mL/min were
significantly associated with failure of access maturation
and need for revision
Duplex testing to estimate brachial artery volume flow can
be performed as a “point-of-care” ultrasound examination
ASSESSMENT OF ACCESS MATURATION
Ko SH, et al. J Vasc Surg. 2015;61(6):1521-1527
Summary
Hemodynamic and anatomic features of access site maturation can
be assessed by duplex scanning
Increases in PSV identify significant stenoses, but with wide variability
Volume flow is the key factor in assessing maturation and predicting
successful dialysis
Measurement of volume flow by duplex ultrasound is subject to errors
but can be performed with acceptable variability
Volume flow can be estimated using brachial artery PSV and EDV
Estimated brachial artery flow of >800 mL/min predicts successful
hemodialysis if anatomic criteria for cannulation are also present
ASSESSMENT OF ACCESS MATURATION