Dialysis Flashcards
Name three types of dialysis
- Haemodialysis
- Haemodiafiltration
- Peritoneal Dialysis
What three process is dialysis based on?
Diffusion
Adsorption
Convection
How is diffusion involved in dialysis?
Moves solutes from a high to low concentration allowing the removal of toxins and infusion of bicarbonate
What is added/removed in dialysis?
Removed - urea, potassium, sodium, creatinine, toxins
Added - pure water, sodium, bicarbonate, potassium, glucose
What rate does blood flow in dialysis?
300-350mls/min
How does convection help dialysis?
Moves the water across the membrane in response to a pressure gradient
What is ultrafiltration?
Convection solute drag pulls the solute with the water
How does adsorption play a role in dialysis?
Affects plasma proteins and solutes bound to them. Proteins stick to the membrane and are removed by binding
What time of membrane adsorbs protein better?
High flux membranes
How is haemodiafiltration different?
Increasing convection allows a larger volume of ultra filtrate. This adds to the solute drag.
Name the factors affecting efficiency of haemodialysis
- water flux
- membrane pore size
- pressure difference
- viscosity of fluid
- size/shape/charge of molecule
If a lot of ultra filtrate is removed what must be done?
Replacement of extra-convective fluid
Define high volume
> 20 litres
How often is haemodialysis given?
4 hours 3 times a week
What are the restrictions a patient but follow if on dialysis?
Fluid 1 litre a day
Low salt to help fluid balance
Low potassium
Low phosphate (with phosphate binders with meals)
Name three ways vascular access can be obtained for dialysis
- tunneled venous catheter
- fistula
- haemodialysis reliable outflow graft
Describe a tunnelled venous catheter
Inserted into large vein - typically internal jugular
What are the pros of catheter?
Easy to insert and can be used immediately
What are the cons of a catheter?
Infection (staph aureus can lead to endocarditis, discitis and death)
Blockage
Damage to central veins which may cause future problems
How are catheter infections managed?
Blood cultures, FBC, CRP and exit site swab
Line should be removed and vancomycin +/- gentamicin
Describe a fistula
Artery and vein surgically connected - the venous part develops to create an enlarged thick walled vessel known as an arteriovenous fistula
Where can a fistula be formed?
Radio-cephalic
Brachio-cephalic
Brachia-basilic transposition
What are the advantages of a fistula?
Good blood flow and lower risk of infection
What are the disadvantages of a fistula?
Requires surgery and can take up to 12 weeks to be fit for use, can limit blood flow to distal arm, thrombose or stenose
State five complications of haemodialysis
- hypotension (underselling of intravascular space)
- haemorrhage (ruptured AVF)
- loss of access (thrombosis/stenosis)
- arrhythmia (electrolyte imbalance)
- cardiac arrest
How does peritoneal dialysis work?
Solute removal by diffusion across the peritoneal membrane. Water is removed by osmosis and driven by high glucose concentration in dialysate fluid
What are the two types of peritoneal dialysis?
- continuous ambulatory
- automated
Describe continuos ambulatory peritoneal dialysis
4 2 litre bag exchanges per day, each lasting 20-30 minutes. Dialysate is drained by gravity and discarded
Describe automated peritoneal dialysis
1 bag of fluid stays in all day and overnight APD machine controls fluid drainage in and out for 9/10 hours
What are the complications of peritoneal dialysis?
- infection
- membrane failure
- hernias
How may infection arise in peritoneal dialysis?
Peritonitis or from exit site, contamination can occur (staph/strep/diptheroids) or translocation from gut (e.coli, klebsiella)
What might happen if the membrane fails?
Unable to remove enough water or solute may need switched to HD
Why does peritoneal dialysis increase risk of hernias?
Increased intra-abdominal pressure requires repair and smaller fill volumes
When might dialysis be started?
Acute Kidney Injury eGFR<7ml/min Urea >40 Unresponsive metabolic acidosis/hyperkalaemia Systemic symptoms
What happens if dialysis is too fast in the beginning?
Disequilibrium syndrome - cerebral oedema, confusion, seizures, death
