Dialysis

Question 1

what are the three concepts of dialysis

Answer 1

diffusion- movement of solutes along con gradient (high to low) across semi permeable membrane to equalise gradient

convection- movement of water (and all dissolved solutes) across a semi permeable membrane in resposne to a pressure gradient- convective solute drag

adsoprtion- plasma proteins (and bound solutes) stick to the membrane surface and are removed by binding

Question 2

what toxins are removed in dialysis

Answer 2

urea
potassium
sodium

Question 3

what is infused into the blood dialysis

Answer 3

(in pure H20)
bicarbonate

(also Na
K
glucose)

Question 4

what is the normal blood flow rate

Answer 4

300-350 mls/ miin

Question 5

how does haemodialysis (HD) work

Answer 5

blood filtered though filaments with semi permeable membranes

Question 6

what is ultrafiltration

Answer 6

convection- removal of water from the blood into the dialysate

Question 7

what membranes are used for adsorption

Answer 7

high flux (absorb protein bound solutes better)

Question 8

what is haemodiafiltration

Answer 8

convective forces causing ultrafiltration then replacing it

Question 9

is haemodialysis diffusion or convection

Answer 9

diffusion

Question 10

what do you replace ultrafiltrate with

Answer 10

ultra pure fluid (ri-infusate)

Question 11

what affects haemodiafiltration

Answer 11

Water flux (rate and volume)

Membrane pore size

The pressure difference (hydrostatic pressure) applied to and across the membrane

Viscosity of the fluid

The size, shape and electrical charge of each molecule

Question 12

what amount of fluid is high volume HDF (haemodiafiltrate)

Answer 12

> 20 litres in 24 hrs

Question 13

what are the benefits of HDF

Answer 13

offer a smoother, less symptomatic treatment than HD

enhances recovery time

improves survival

similar cost to conventional HD

Question 14

how efficient is dialysis

Answer 14

not- long treatment times

Question 15

what restrictions must the patient on dialysis follow

Answer 15

fluid- if anuric 1 litre/ day (inc food)
low salt
low potassium
low phosphate (take phosphate binders with meals)

Question 16

what are the vascular access options in dialysis

Answer 16

tunneled venous catheter (usually into IJV- easy to insert, high risk of infection, can cause vascular damage)

fistula (gold standard) (artery and vein surgically connected - venous part develops thich walled arteriovenous fistula ) (less likely yo get infections, requires surgery, 6-12 weeks before use, can limit blood flow to distal arm (steal syndrome))

hemodialysis reliable outflow graft (2nd best)

Question 17

what infections are seen in tunneled venous catherters

Answer 17

s aureus (endocarditis, discitis, death)

Question 18

where can you get a fistula created

Answer 18

radio-cephalic
brachio-cephalic
brachio-cephalic transposition

Question 19

what can go wrong in dialysis

Answer 19

hypotension
haemorrhage (ruptured AVF)- life threatening
loss of vascular access (thrombosis, stenosis, infection)
arrhythmia (electrolyte imbalance, myocardial ischaemia)
cardiac arrest

Question 20

what causes intra-dialytic hypotension

Answer 20

aka ‘myocardial shunning’
removal of large volumes of water
under filling of the intravascular space and low BP

Question 21

how does peritoneal dialysis work

Answer 21

dialysate fluid line and catheter inserted into peritoneum (peritoneal fluid)

Solute removal by diffusion of solutes across the peritoneal membrane (semi-permeable membrane) (from blood into peritoneum)

Water removal by osmosis (water moving to equalize a concentration gradient) - driven by high glucose concentration in dialysate fluid

PD dialysate drained by catheter

can also be automated where drained by a APD machine overnight

Question 22

what can go wrong in peritoneal dialysis

Answer 22

Infection
Peritonitis or exit site infection (contamination, gut bacteria translocation)

peritoneal membrane failure (fluid overload/ uraemic (cant remove solutes))

hernias (increased abdo pressure)

Question 23

what is the management for a PD infection

Answer 23

Culture PD Fluid

Intra-peritoneal antibiotics
Gram positive
Gram Negative

May need catheter removal

Question 24

when do you start dialysis

Answer 24

based on blood tests:
Resistant hyperkalaemia

eGFR < 7 ml/min

Urea > 40 mmol/L

Unresponsive metabolic acidosis

based on symptoms:
Nausea
Anorexia
Vomiting
Profound fatigue
Itch
Unresponsive fluid overload

Question 25

why do you have to build up to a four hr session in HD (start at 90-120 mins)

Answer 25

Too-rapid a correction of uraemic toxin levels can lead to Disequilibrium syndrome:
Cerebral oedema and possible confusion, seizures and occasionally death

Question 26

how do you start

PD

Answer 26

Training (3-6 weeks after PD catheter insertion)

Starts with smaller ‘fill volumes’

Fill volumes increase in size to ~ 2.0-2.5L

Regular clinic and nurse follow up

Question 27

why should some people not get dialysis

Answer 27

In ESRD, as age increases, survival with RRT decreases
Patients > 75, with numerous co-morbidities, are expected to have similar number of ‘hospital free’ days whether starting HD or not
Quality of life Vs Quantity of life (patient to make an informed choice)
RRT is expensive and healthcare budget is not limitless

Question 28

what medical reasons might you withdraw from dialysis

Answer 28

Haemodynamic instability
Progressive dementia
Inability to remain on therapy for full duration due to agitation
Cardiovascular event
Terminal cancer

Question 29

what social reasons might you withdraw from dialysis

Answer 29

Increasing fraility and inability to cope at home

Question 30

what is the best form of renal replacement therapy

Answer 30

transplant- dialysis stopgap before this in those who are suitable

Question 31

can you get dialysis at home

Answer 31

yes

Question 32

how does dialysis affect QoL

Answer 32

badly