duplex assessment of dialysis access maturation

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


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


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


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


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


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


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


Volume Flow: Examples Good Diameter

Doppler angle

Sample volume

Mean tracker

Flow pattern


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



Brachial Artery vs. Access ConduitVolume Flow Measurements

Brachial Artery PSV vs. Volume Flow



Brachial Artery Velocities and Volume Flow Categories


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


*EDV/PSV ratio is an indicator of outflow resistance, with higher values representing the low resistance expected in a normally functioning access site



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%)


*P<.0001



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



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


duplex assessment of dialysis access maturation

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