Dialysis

Question 1

What are the 3 concepts of Dialysis?

Answer 1

Diffusion

Convection

Adsorption

Question 2

What is meant by diffusion?

Answer 2

Movement of solutes from high to low concentration

Gradient to equilibriate on both sides of a semi permeable membrane

Question 3

Dialysis removes which toxins that build up in ESRD?

Answer 3

Urea
Potassium
Sodium

Question 4

What compound is infused when on dialysis?

Answer 4

Bicarbonate

Question 5

What is a normal blood flow rate on haemodialysis?

Answer 5

~ 300-350 mls/min depending on site

Tunnelled Catheter is lower at around 300 mls/min
Fistula = larger => can extend to 350/400 mls/min

Question 6

What is dialysate?

Answer 6

Purified water

Na, HCO3, K and Glucose can be added to in order to suit the patient

Question 7

What is meant by convection?

Answer 7

movement of water (and solutes dissolved in it) across a semi-permeable membrane in response to a pressure gradient
Also known as “ULTRAFILTRATION”

Question 8

How does haemodialysis promote the removal of water?

Answer 8

Sets up a pressure gradient where the blood is higher than the dialysate

Question 9

What is the main function of the microfilaments in the dialysis equipment which acts as an external kidney?

Answer 9

The increase the surface area available for exchange of water
Dialysate runs upwards as blood runs downwards

Question 10

Adsorption affects what component of blood?

Answer 10

• Plasma proteins and solutes bound to them

- Plasma proteins of low molecular weight stick to the membrane surface and are removed by membrane binding

Question 11

High flux membranes adsorb protein-bound solutes better than low flux membranes. TRUE/FALSE?

Answer 11

TRUE

Question 12

What is the difference between haemodialysis and haemodiafiltration?

Answer 12

HD uses diffusion

HDF uses convection

Question 13

Longer treatment times = better efficiency in haemodialysis. TRUE/FALSE?

Answer 13

TRUE

Question 14

What must patients be warned if they choose to decrease their dialysis time?

Answer 14

Increased risk of death - 1% for every 30 mins less

Question 15

How often is a patient usually on dialysis and for how long are they on the machine at a time?

Answer 15

4 hours

3 days a week

Question 16

What restrictions do dialysis patients have to put on their diets?

Answer 16

Fluid (including foods which metabolise to H2O)
Salt
Potassium (avoid Banana, chocolate, potato, avocado)
Phosphate (or phosphate binders with meals)

Question 17

What options are there for vascular access in dialysis?

Answer 17

Arteriovenous Fistula (AVF = Scribner Shunt)
Tunnelled Catheter

Question 18

What vein is a tunnelled catheter usually inserted into?

Answer 18

Internal jugular

Question 19

What are the potential complications of a tunnelled catheter?

Answer 19

• infection
• blockage
• damage (stenosis/ thrombosis) to central veins can make future line insertion difficult

Question 20

What are the main complications of arteriovenous fistulae?

Answer 20

• Require surgery

- Usually requires maturation of 6 – 12 weeks before can be used

Question 21

What sites are used to establish arteriovenous fistulae?

Answer 21

Radio-Cephalic (RC AVF)
Brachio-Cephalic (BC AVF)
Brachio-Basilic transposition (BB AVF)

Question 22

What types of graft can be used in dialysis?

Answer 22

Arteriovenous graft
=> between Cephalic vein and Brachial artery

HeRO Graft (Hemodialysis Reliable Outflow Graft)
=> either into Right Atrium OR Left subclavian

Question 23

What can potentially go wrong in dialysis?

Answer 23

• Hypotension (can mimic cardiac arrest)
• Haemorrhage
• Loss of vascular access
• Arrhythmia /Cardiac arrest

Question 24

Why does dialysis cause hypotension and myocardial stunning?

Answer 24

Removing large volumes of H20 3x per week
rather than continuously with normal kidneys
=> Leads to under-filling of the intravascular space and low BP

Question 25

How does peritoneal dialysis work?

Answer 25

Solute removal by diffusion across the peritoneal membrane

Water removal by osmosis
- driven by high glucose concentration in dialysate fluid

Question 26

How often does Continuous Ambulatory Peritoneal dialysis need changing?

Answer 26

4 x 2L bag exchanges per day

PD dialysate drained then fresh bag instilled

Takes 20-30 mins to exchange

Question 27

How often is Automated Peritoneal Dialysis changed?

Answer 27

1 bag of fluid stays in all day

Overnight APD machine controls fluid drainage in and out for ~ 9-10 hours per night

Question 28

What are the main complication of peritoneal dialysis?

Answer 28

Peritoneal
Exit site infection
Peritoneal membrane failure
Hernias

Question 29

What blood tests would prompt starting dialysis?

Answer 29

• Resistant hyperkalaemia
• eGFR < 7 ml/min
• Urea > 40 mmol/L
• Unresponsive metabolic acidosis

Question 30

How long should the first session of dialysis last in order to build up to the 4 hours?

Answer 30

90-120 minutes

Question 31

What is Disequilibrium syndrome?

Answer 31

• Too-rapid a correction of uraemic toxin levels
• Cerebral oedema
• possible confusion
• seizures
• occasionally death

Question 32

How long do patients need to train to administer peritoneal dialysis ?

Answer 32

3-6 weeks after PD catheter insertion

Question 33

For what reasons may dialysis be withdrawn?

Answer 33

• Haemodynamic instability
• Progressive dementia (pull out catheter etc)
• Inability to remain on therapy for full duration due to agitation
• Cardiovascular event
• Terminal cancer