Hemodialysis Access Grafts and Fistulae (Jaycie)

Autogenous definition

Self generated or produced independently

AVF or AVG eliminates excess fluid and

Decreases undesirable substances in the body

These are more common in arms or legs?

Arms

You want to start as far ______ as possible with the fistula. Why?

Distal bc the success rate is not high so you can start low and keep trying

AVF definition

Abnormal connection between an artery and a vein that can occur spontaneously, as a result of trauma or surgically performed for hemodialysis access

What is dialysis?

•Treatment for renal failure
• Dialysis is a method for filtering the blood externally
• Blood is removed from the artery, filtered through a dialysis machine, then returned to the body via the vein

Requirement for dialysis

High blood volumes

Dialysis is accomplished by

The creation of AVF - a connection between an artery and a vein called dialysis access

_________ access preferred for superior patency rates and lower complications

Autogenous

Upper or lower extremities are preferred

Upper

Do autogenous fistulas or synthetic grafts have better long-term patency?

Autogenous fistulas bc they have lower maturation rate and higher early thrombosis rate

AV fistula success rate at the two year mark

40-60%

AV graft success rate at 2 year mark

18-30%

Preoperative evaluation

Vein mapping is performed to determine suitability of veins for placement of fistula

Duplex assessment can be performed

-Before pt begins hemodiaysis
-In pts who have undergone other access procedures

Cephalic and basilic veins are ______

Superficial
-We want to use superficial

Types of dialysis access - synthetic grafts

Straight graft and loop graft

Synthetic grafts are made of

PTFE (Gortex) - synthetic material used to connect an artery to a vein may be straight or loop

In a ________ we tie the vein and artery together

Fistula

Native autogenous fistula

The vein is connected directly to the artery

Breccia-Cimino fistular:

Describes a radial artery to a cephalic vein

Contraindications to the procedure:

◦Central venous catheters
◦Pacemakers
◦Defibrillators
◦Prior mastectomy

AVF vein luminal diameter should be

Greater than 2.5mm at the anastomosis site

AVG the vein should be

Greater than 4mm at the anastomosis site

Pre-op assessment of venous system include:

B-mode imaging making sure there is no thrombus, webbing, calcium
-Walls should be compressible
-Document patency, depth, wall thickness

Webbing is

Scar tissue

Subclavian vein has a respirator phasicity... what does this mean and is it good or bad?

Meaning it goes with pts breathing
- This is good/normal we do not want a continuous waveform

Contrindications include:

Intravenous lines Open wounds
Limited patient positioning Dressings
Localized infections

Evaluation of hemodialysis

Should have a palpable thrill and an audible bruit

Calculate volume flow equation:

Q = graft area x TAV x 60 sec

TAMV meaning

Time average mean velocity

TAV measured in cm/sec should obtain

3-4 cardiac cycles
**TEST**

Volume flow for graft is anything above _____mL/min but below ______mL/min

800mL/min but below 1500mL/min

Venous anastomosis and outflow vein is most common site for

Stenosis
-Typically a hyperplasia response to high flow rate/ increased shear stress as well as trauma

General velocity criteria for >50% stenosis chart:
At the anastomosis:
-PSV > or equal to 400cm/sec
-Velocity ratio >3
-Intraluminal defect

Along the venous outflow: (after connection)
-PSV> or equal to 300cm/sec
-Velocity ratio >2
-Velocities <50cm/sec

Velocity or Volume flow?
- Identifies a stenosis

Velocity

Velocity or volume flow?
Does not relate to performance

Velocity

Velocity or volume flow?
-Indicates performance of access

Volume flow

Velocity or volume flow?
-Suggests but does not identify a stenosis

Volume flow

Velocity or volume flow?
-Useful to follow trends in individual patients

Velocity and volume flow

Volume flow determines the

Accessibility

Fistula occlusion

• Often evident on the clinical exam but is relatively easy to determine with imaging. Note the visualized vessel with no flow in the access despite a diligent search. Frequently the artery will remain patent

Extravascular Mass:
Anechoic mass with no flow

Seroma
Hematoma
Thrombosed pseudoaneurysm

Active blood flow outside the vessel

Pseudoaneurysm
Yin-Yang sign

Large blood volume moving through the fistula does not perfuse the body and therefore may impact cardiac function (CHF)

Steal

Arterial blood flow distal to the fistula is reversed flowing into the venous circulation May result in hand ischemia (pain, pallor(paleness), even ulceration)

Steal syndrome

Most common site of stenosis or occlusion of hemodialysis access graft?

Outflow vein