Dialysis

Question 1

What are the three concepts that underlie dialysis?

Answer 1

Diffusion, convection and adsorption

Question 2

What does dialysis allow?

Answer 2

Removal of toxins which build up with ESRD (e.g urea, sodium, potassium) and infusion of bicarbonate

Question 3

What is haemodialysis?

Answer 3

Blood is removed from the body and filtered through a man-made membrane called a dialyser
Filtered blood is then returned to the body

Question 4

What are the contents of the dialysate when it is removed and returned to the body?

Answer 4

Leaving = urea, creatine, Na+, K+, other toxins
Entering = pure H2O, Na+, K+, HCO3-

Question 5

How does haemodialysis get rid of water?

Answer 5

Ultrafiltration = negative pressure of 100-200 mmHg needed to cause convective solute drag

Question 6

What is ultrafiltration?

Answer 6

Movement of water and the solutes dissolved in it across a semi-permeable membrane in response to a pressure gradient

Question 7

What is principally affected by adsorption?

Answer 7

Plasma proteins and any solutes that might be bound to them

Question 8

What happens to plasma proteins?

Answer 8

Stick to the membrane surface and are removed by membrane binding (especially those of low molecular weight)

Question 9

Which membranes adsorb protein-bound solutes best?

Answer 9

High flux membranes are better at adsorbing than low flux membranes

Question 10

What is the difference in mechanism between haemodialysis and haemodiafiltration?

Answer 10

Haemodialysis is primarily diffusive whilst haemodiafiltration is increasingly convective in nature

Question 11

What effect does increasing the convective force in haemodiafiltration have?

Answer 11

The greater the convective force, the greater the generated volume of the pressure-driven ultrafiltrate

Question 12

What effect does large volumes of ultrafiltrate have?

Answer 12

Adds enormously to solute drag, especially for the larger middle molecule solute class

Question 13

How does diffusion occur in haemodiafiltration?

Answer 13

Down engineered concentration gradients

Question 14

What are some factors that affect the efficiency of convective transport?

Answer 14

Water flux (rate and volume)
Viscosity of fluid within membrane pores 
Membrane pore size = big/little holes, and their ratios
Hydrostatic pressure difference across membrane
Size, shape and electrical charge of molecules

Question 15

What is the key difference between haemodialysis and haemodiafiltration?

Answer 15

Replacement of extra-convective ultrafiltrate, throughout the dialysis period (minus any intended ultrafiltration volume)

Question 16

Why is the composition and purity of the replacement fluid given in haemodiafiltration important?

Answer 16

Re-infusate is given directly into the patient’s circulation

Question 17

What is high volume haemodifiltration defined as?

Answer 17

Replacement volumes >20 litres

Question 18

What are the benefits of haemodiafiltration?

Answer 18

Offers smoother, less symptomatic treatment than HD
Enhances recovery time and improves survival
Achieves results at a similar cost to conventional HD

Question 19

What is the minimum dialysis prescription?

Answer 19

4hrs, 3 times a week

Question 20

What effect does decreasing dialysis time have?

Answer 20

Increases risk of death = 1% for every 30mins

Question 21

What are the restrictions put on dialysis patients?

Answer 21

Fluid = if anuric then 1L/day (including food based fluid)
Salt = low salt diet to reduce thirst and help fluid balance
Potassium = low potassium diet
Phosphate = low phosphate diet, phosphate binders with meals (6-12 pills per day)

Question 22

What are different ways of gaining vascular access for dialysis?

Answer 22

Scribner shunt, tunnelled venous catheter, fistula, arteriovenous graft, haemodialysis reliable outflow graft

Question 23

What are some features of a Scribner shunt?

Answer 23

Original form of vascular access to the blood stream to allow maintenance haemodialysis, allows dialysis for both AKI and ESRD

Question 24

How are tunnelled venous catheters inserted?

Answer 24

Catheter inserted into a large vein, usually the internal jugular vein

Question 25

What are the pros and cons of tunnelled venous catheters?

Answer 25

``` Pros = easy to insert, can be used immediately Cons = high risk of infection, can become blocked, can stenose/thrombose making future line insertion difficult ```

Question 26

What are some features of infections caused by tunnelled venous catheters?

Answer 26

Staph aureus = endocarditis, discitis, death Do blood cultures, FBC, CRP and exit site swab Treat with vancomycin +/- gentamicin May need to remove or exchange line

Question 27

What is the gold standard method of gaining vascular access for dialysis?

Answer 27

Fistula = artery and vein are surgically connected

Question 28

What happens to the venous part of the fistula?

Answer 28

Develops to create an enlarged, thick walled vessel called an arteriovenous fistula (AVF)

Question 29

Where are some common sites for fistulas to be formed?

Answer 29

In both upper limbs = radio-cephalic, brachio-cephalic, brachio-basilic transposition

Question 30

What are the pros and cons of fistulas?

Answer 30

``` Pros = good blood flow, less likely to cause infection Cons = requires surgery, needs maturation of 6-12 weeks before use, thrombosis/stenosis ```

Question 31

What is steal syndrome?

Answer 31

Limited blood flow to distal arm caused by a fistula

Question 32

What are the risks of dialysis?

Answer 32

Hypotension and cardiac arrest Haemorrhage = life threatening if ruptured AVF Loss of vascular access Arrhythmia = electrolyte imbalance, ischaemia

Question 33

What causes intra-dialytic hypotension?

Answer 33

Myocardial stunning on dialysis = underfilling of intravascular space and low BP due to removal of large volume of H20 three times a week (rather than continuously)

Question 34

How does peritoneal dialysis work?

Answer 34

Solutes removed by diffusion across peritoneal membrane, water removed by osmosis driven by high glucose concentration of dialysate fluid

Question 35

What are the types of peritoneal dialysis?

Answer 35

Continuous ambulatory peritoneal dialysis and automated peritoneal dialysis

Question 36

How is continuous ambulatory peritoneal dialysis carried out?

Answer 36

Four 2L bag exchanges per day, PD dialysate drained then fresh bag instilled, 20-30 mins per exchange

Question 37

How is automated peritoneal dialysis carried out?

Answer 37

1 bag of fluid stays in all day, overnight machine controls fluid drainage in and out for 9-10hrs per night

Question 38

What are the complications of peritoneal dialysis?

Answer 38

Peritonitis or exit site infection Peritoneal membrane failure Hernias = require repair and smaller fill volumes

Question 39

What are some features of peritonitis and exit site infections caused by PD?

Answer 39

Contamination (staph, strep, diptheroids) or gut bacteria translocation (E.coli, klebsiella) Must culture PD fluid and may need to remove line Give intra-peritoneal antibiotics

Question 40

What is peritoneal membrane failure?

Answer 40

Inability to remove enough water (causing fluid overload) and solutes (causing uraemia) = requires switch to haemodialysis

Question 41

What blood test would be indicative of starting dialysis?

Answer 41

Resistant hyperkalaemia, eGFR <7 ml/min, urea >40 mmol/l, unresponsive metabolic acidosis

Question 42

What symptoms may be indicative of starting dialysis?

Answer 42

Nausea, anorexia, vomiting, profound fatigue, itch, unresponsive fluid overload

Question 43

How is haemodialysis started?

Answer 43

Gradual build up = first session of 90-120 mins then subsequent sessions building up to 4hrs

Question 44

Why is it important to start haemodialysis slowly?

Answer 44

Too rapid a correction of uraemic toxin levels can lead to disequilibrium syndrome

Question 45

What are the features of disequilibrium syndrome?

Answer 45

Cerebral oedema, possible confusion, seizures, death

Question 46

How is peritoneal dialysis started?

Answer 46

Training = 3-6 weeks after catheter insertion Start with smaller fill volumes = increase to 2-2.5L Regular clinic and nurse follow up

Question 47

What effect does age have on dialysis survival in patients with ESRD?

Answer 47

As age increases, survival with dialysis decreases

Question 48

Does dialysis make a huge improvement for patients over 75 with many co-morbidities?

Answer 48

Not really = expected to have similar number of hospital free days whether starting HD or not

Question 49

What are some reasons for withdrawing dialysis?

Answer 49

Haemodynamic instability, progressive dementia, CV event, terminal cancer, inability to remain on therapy for full duration due to agitation, increasing frailty and inability to cope at home