Dialysis

Question 1

what are the 3 main concepts in dialysis

Answer 1

diffusion
convection
adsorption

Question 2

what is diffusion

Answer 2

movement of solutes from high to low concentration gradient to equalise the concentrations

Question 3

what does diffusion allow in dialysis

Answer 3

removal of toxins and water products
(urea, K and Na)
infusion of bicarbonate

Question 4

what happens when the blood enters the dialysis machine

Answer 4

it looses K Urea and Na through a semi permeable membrane into the dialysis fluid

it gains bicarbonate from the dialysis fluid into the blood

Question 5

what is in the dialysis fluid (dialysate)

Answer 5

pure H20 
Na 
HCO3 
K
Glucose

Question 6

how does haemodialysis get rid of water

Answer 6

through convection

water (and solutes dissolved in it) are moved across the semipermeable membrane by a PRESSURE gradient

Question 7

what is ultrafiltration

Answer 7

the removal of water from the blood via a pressure gradient

there is negative pressure in the dialysate which pulls the water out

Question 8

what happens to plasma proteins during haemodialysis

Answer 8

they often stick to the membrane surface and get removed by membrane binding

Question 9

what is the difference between haemodialysis and haemodiafiltration

Answer 9

haemodyalisis is mainly diffusive

haemodiafiltration is mainly convective (uses pressure)

Question 10

what is the effect of the ultra filtrate in haemodiafiltration

Answer 10

high convective force produces lots of ultra filtrate

this sets up a solute - drag which pulls out larger ‘middle molecules’

there is diffusion down engineered concentration gradients

Question 11

what things affects the efficiency of the convective transport in haemodiafiltration

Answer 11

water flux
membrane pore size
pressure difference across membrane (hydrostatic)
viscosity of the fluid
size, shape and electrical charge of the molecules

Question 12

what is the key difference between HD and HDF

Answer 12

in HDF replacement fluid is given to the patient to replace the loads of ultra filtrate taken out

High volume HDF has replacement volumes of >20 litres

Question 13

what are the benefits of HDF

Answer 13

• smoother, less symptomatic treatment
• enhances recovery time
• improves survival

Question 14

what makes dialysis more efficient

Answer 14

longer treatment times

Question 15

what is the minimum HD/HDF prescription

Answer 15

4 hours

3 times a week

Question 16

what happens when you decrease dialysis time by 30 mins

Answer 16

it gives a 1% increased risk of death

Question 17

what restrictions does dialysis put on the patients diet

Answer 17

• Must reduce fluid to 1 L per day
• Low salt diet (helps reduce thirst and helps fluid balance)
• Low potassium diet
• Low phosphate diet

Question 18

what are the options for gaining vascular access for dialysis

Answer 18

Tunneled venous catheter
Fistula
Atriovenous graft
HeRO graft

Question 19

what is a tunnelled venous catheter

Answer 19

a catheter inserted into a large vein - usually internal jugular

Question 20

what are the pros of a tunnelled venous catheter

Answer 20

easy to insert

can be used immediately

Question 21

what are the cons of a tunnelled venous catheter

Answer 21

• high risk of infection
• can become blocked
• can cause damage to veins making line insertion difficult in future

Question 22

what infections do you tend to get with tunnelled venous catheters

Answer 22

STAPH AUREUS

leads to

• endocarditis
• discitis
• death

Question 23

treatment for tunnelled venous catheter infection

Answer 23

antibiotics

-vancomycin +/- gentamicin as empirical until cultures are back

Question 24

what is a arteriovenous fistula

Answer 24

the gold standard for vascular access

artery and vein surgically connected to form a thick walled enlarged vessel

Question 25

what are the pros of an arteriovenous fistula

Answer 25

good blood flow | less likely to cause infection

Question 26

cons of an arteriovenous fistula

Answer 26

required surgery needs maturation of 6-12 weeks before use can limit blood flow to distal arm can thrombose or pentose

Question 27

what is an arteriovenous graft

Answer 27

a graft that connects an artery to a vein

Question 28

what is a HeRO graft

Answer 28

for complex access long graft with venous component on one side and arterial much further down canulation area is in the middle of the graft

Question 29

complications of dialysis

Answer 29

``` hypotension haemorrhage (ruptured fistula) loss of vascular access arrhythmia cardiac arrest ```

Question 30

what is peritoneal dialysis

Answer 30

then the solute is removed by diffusion across the peritoneal membrane water removed by osmosis driven by a high glucose concentration in the dialysate fluid

Question 31

what is continuous ambulatory peritoneal dialysis

Answer 31

dialysis that can be done at home 4x2L bag exchanges per day peritoneal dialysate is drained and a fresh back is installed takes 20-30 mins per exchange

Question 32

what is automated peritoneal dialysis

Answer 32

1 bag of fluid stays in outside the peritoneum all day an overnight ADP machine controlled fluid drainage in and out for 9-10 hours per night

Question 33

what are the complications of peritoneal dialysis

Answer 33

infection -peritonitis or exit site infection Peritoneal membrane failure Hernia

Question 34

what bacterial tend to cause infection in peritoneal dialysis

Answer 34

contamination from: staph strep diptheriods gut commensals: e.coli klebseilla

Question 35

how do you manage infection in peritoneal dialysis

Answer 35

culture peritoneal dialysate intraperitoneal antibiotics may need catheter removal (if entry site)

Question 36

what is peritoneal membrane failure

Answer 36

inability of the membrane to remove enough water due to fluid overload inability to remove enough solutes needs switch to HD

Question 37

how does PD cause hernias

Answer 37

due to the increased intra-abdominal pressure required hernia repair and smaller fill volumes

Question 38

when should you star dialysis based on bloods

Answer 38

resistant hyperkalaemia eGFR <7 urea >40 Uresponsive metabolic acidosis

Question 39

when should you start dialysis based on symptoms

Answer 39

if there is: ``` nausea vomiting anorexia profound fatigue itch unresponsive fluid overload ```

Question 40

how do you start haemodialysis

Answer 40

gradual build up first session lasts 90-120 mins and build up to 4 hours

Question 41

what happens if uraemic. toxin levels are corrected too rapidly

Answer 41

disequilibrium syndrome - cerebral oedema - confusion - seizures - death (occasionally)

Question 42

when should you stop dialysis

Answer 42

- haemodynamic instability - progressive dementia - Inability to remain on therapy for full duration due to agitation - cardiovascular event - terminal cancer unable to cope at home - increasing frailty you then need palliative care involvement