Hemodialysis AV Fistulas

Hemodialysis AV Fistula

Anastomosis of artery & vein

Reliable, repeatable hemodialysis access with minimal complications

Types of Anastomoses

Site Preferences for AV Fistula

Non dominant forearm

Dominant forearm

Non dominant upper arm

Dominant upper arm

Lower extremity

Preferred Site for AV Fistula

As distal as possible in non-dominant arm

Why is the upper extremity preferred for AV fistulas?

Patient comfort & preference

Lower infection rates

Greater longevity

Easier to access

Patient Prep & Assessment

Keep room warm

Patient in supine/sitting position

Take bilateral blood pressures

Take pulses of brachial, radial, and ulnar arteries

Allen Test: assesses for intact palmar arch - clenched fist - reactive hyperemia after compression indicates patency

Assess superficial veins using tourniquets

Fistula Maturation Failure

Caused by obligatory use of small/suboptimal veins

Quality of Artery

Determines capacity to dilate & accommodate increased flow

Fistula/Graft Mapping

Find suitable artery before moving onto venous system

AV Fistula & Hemodialysis Graft Arterial Mapping

Start with distal forearm of non-dominant arm

Assess for plaque, thickening, stenosis, compliance

Evaluate waveform & note PSV - high resistant (rapid upstroke, sharp peak, low diastolic flow)

Arterial Diameter for Fistulas/Grafts

> 2.5 mm

AV Fistula & Hemodialysis Graft Venous Mapping

Start with superficial system of non-dominant forearm

Begin with cephalic, basilic, and median cubical veins at wrist and move proximally to axilla

Assess for thrombus, compressibility, narrowing, tributaries , scarring- central veins have respirophasicity & cardiac pulsatility

Compress & record diameter every 2 cm

Doppler with augmentation (include subclavian & IJV)

Measure vein diameter with & without tourniquet (2 tourniquets-at axillary & forearm-for 3 minutes)

Assess depth from skin surface to anterior wall of vein

Vein Diameter for Fistulas/Grafts

> 2.5 mm

Vein Diameter for Synthetic Fistulas/Grafts

≥ 4 mm

Basilic Vein Length for Fistulas/Grafts

≥ 10 cm

Pre-Mapping Contraindications for AV Fistula Placement

Thrombus

Calcifications

Thickened vessels

Local infection

Dressings that can't be removed

Open wounds

AV Fistula/Graft Maturity

Occurs 6 weeks - 6 months after placement

Assess 10-12 weeks after placement before hemodialysis begins

Mature AV Fistula/Graft

Drop in peripheral resistance

Can handle 6 cycles a month

Audible swishing bruit

Palpable thrill/vibration - turbulent flow at anastomosis

Large enough for two 15-gauge needles

Normal PSV for Fistula

100-400 cm/sec

Normal EDV for Fistula

60-200 cm/sec

Fistula Surveillance

Fistula diameters

Depth from skin surface

PSV's of:

- Native artery prox to anastomosis/arterial inflow

- Arterial anastomosis

- Throughout fistula - walk-through technique

- Venous outflow

Assess patency of all inflow arts/outflow veins

Arterial Side of Fistula

Low-resistant waveform

Venous Side of Fistula

High flow volume

Pulsatile prox to anastomosis

Normal Fistula Inflow Artery

Proximal to anastomosis

Low resistant - forward diastolic flow & spectral broadening

Normal Fistula Flow

1 cm below skin

Low resistant - forward diastolic flow & spectral broadening

Elevated PSV & EDV velocities

Normal Venous Outflow

Pulsatile flow

Acquiring Flow Volume of a Mature Fistula

Evaluate function at mid-fistula

Large sample volume (wide as vessel)

Measure diameter on grayscale

Use auto-tracing or trace 3-4 waveforms for mean velocity

Take at least 3 times

Normal Flow Volume of a Mature Fistula

> 800 ml/min

AV Fistula & Graft Complications

Immaturity

Stenosis

Occlusion

Thrombosis

Aneurysm and Pseudoaneurysm

Fluid collections

CHF

Arterial Steal Syndrome

Immature AV Fistula

Proximal hammer pulse

Minimal thrill

Lack of venous distention

Lack of high-pitched bruit

Signs of stenosis & palpable distal thickening

AV Fistula Stenosis

Most common in venous anastomosis & outflow vein

Echogenic intraluminal lesion

Flow reduction

Mild/Moderate Stenosis Flow Volume

500-800 ml/min

Severe Stenosis Flow Volume

< 500 ml/min

PSV of AV Fistula Stenosis

> 375 cm/sec

PSV Ratio for > 50% Stenosis on Arterial Side

> 3:1

PSV Ratio for > 50% Stenosis on Venous Side

> 2:1

AV Fistula Occlusion

Absent flow in lumen

Echogenic thrombus in lumen

Prox high-resistant flow

AV Fistula Thrombosis

To and Fro flow- inflow

Low PSV

Absence of color flow & no outflow

Echogenic material

AV Fistula Aneurysm

AV Fistula Pseudoaneurysm

AV Fistula Fluid collections

Arterial Steal Syndrome

Occurs in 75-90% of patients

Most patients are asymptomatic

Due to poor distal collateral circulation & high flow through fistula

Low-resistant outflow vein draws antegrade flow from inflow artery & steals retrograde flow from distal artery

Failing AV Fistula/Graft Interventions

Percutaneous transluminal angioplasty

Percutaneous recanalization

Interoperative branch ligation

Interoperative revision and vein interposition

DRIL procedure

DRIL Procedure

Ligation of native artery distal to dialysis access

Bypass from native artery to artery distal to ligation

Complimentary Imaging for AV Fistula Mapping/Monitoring

Venography

Enhanced MR Venogram