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Renal > Dialysis > Flashcards

Dialysis Flashcards

1
Q

What are the three concepts that underlie dialysis?

A

Diffusion, convection and adsorption

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2
Q

What does dialysis allow?

A

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

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3
Q

What is haemodialysis?

A

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

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4
Q

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

A 
Leaving = urea, creatine, Na+, K+, other toxins
Entering = pure H2O, Na+, K+, HCO3-
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5
Q

How does haemodialysis get rid of water?

A

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

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6
Q

What is ultrafiltration?

A

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

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7
Q

What is principally affected by adsorption?

A

Plasma proteins and any solutes that might be bound to them

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8
Q

What happens to plasma proteins?

A

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

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9
Q

Which membranes adsorb protein-bound solutes best?

A

High flux membranes are better at adsorbing than low flux membranes

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10
Q

What is the difference in mechanism between haemodialysis and haemodiafiltration?

A

Haemodialysis is primarily diffusive whilst haemodiafiltration is increasingly convective in nature

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11
Q

What effect does increasing the convective force in haemodiafiltration have?

A

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

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12
Q

What effect does large volumes of ultrafiltrate have?

A

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

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13
Q

How does diffusion occur in haemodiafiltration?

A

Down engineered concentration gradients

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14
Q

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

A 
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
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15
Q

What is the key difference between haemodialysis and haemodiafiltration?

A

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

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16
Q

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

A

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

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17
Q

What is high volume haemodifiltration defined as?

A

Replacement volumes >20 litres

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18
Q

What are the benefits of haemodiafiltration?

A

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

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19
Q

What is the minimum dialysis prescription?

A

4hrs, 3 times a week

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20
Q

What effect does decreasing dialysis time have?

A

Increases risk of death = 1% for every 30mins

21
Q

What are the restrictions put on dialysis patients?

A 
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)
22
Q

What are different ways of gaining vascular access for dialysis?

A

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

23
Q

What are some features of a Scribner shunt?

A

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

24
Q

How are tunnelled venous catheters inserted?

A

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

25
Q

What are the pros and cons of tunnelled venous catheters?

A 
Pros = easy to insert, can be used immediately
Cons = high risk of infection, can become blocked, can stenose/thrombose making future line insertion difficult
26
Q

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

A

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

27
Q

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

A

Fistula = artery and vein are surgically connected

28
Q

What happens to the venous part of the fistula?

A

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

29
Q

Where are some common sites for fistulas to be formed?

A

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

30
Q

What are the pros and cons of fistulas?

A 
Pros = good blood flow, less likely to cause infection
Cons = requires surgery, needs maturation of 6-12 weeks before use, thrombosis/stenosis
31
Q

What is steal syndrome?

A

Limited blood flow to distal arm caused by a fistula

32
Q

What are the risks of dialysis?

A

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

33
Q

What causes intra-dialytic hypotension?

A

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)

34
Q

How does peritoneal dialysis work?

A

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

35
Q

What are the types of peritoneal dialysis?

A

Continuous ambulatory peritoneal dialysis and automated peritoneal dialysis

36
Q

How is continuous ambulatory peritoneal dialysis carried out?

A

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

37
Q

How is automated peritoneal dialysis carried out?

A

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

38
Q

What are the complications of peritoneal dialysis?

A

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

39
Q

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

A

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

40
Q

What is peritoneal membrane failure?

A

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

41
Q

What blood test would be indicative of starting dialysis?

A

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

42
Q

What symptoms may be indicative of starting dialysis?

A

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

43
Q

How is haemodialysis started?

A

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

44
Q

Why is it important to start haemodialysis slowly?

A

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

45
Q

What are the features of disequilibrium syndrome?

A

Cerebral oedema, possible confusion, seizures, death

46
Q

How is peritoneal dialysis started?

A

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

47
Q

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

A

As age increases, survival with dialysis decreases

48
Q

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

A

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

49
Q

What are some reasons for withdrawing dialysis?

A

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

Renal (36 decks)

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