Dialysis Flashcards
What are the 3 concepts of Dialysis?
Diffusion
Convection
Adsorption
What is meant by diffusion?
Movement of solutes from high to low concentration
Gradient to equilibriate on both sides of a semi permeable membrane
Dialysis removes which toxins that build up in ESRD?
Urea
Potassium
Sodium
What compound is infused when on dialysis?
Bicarbonate
What is a normal blood flow rate on haemodialysis?
~ 300-350 mls/min depending on site
Tunnelled Catheter is lower at around 300 mls/min
Fistula = larger => can extend to 350/400 mls/min
What is dialysate?
Purified water
Na, HCO3, K and Glucose can be added to in order to suit the patient
What is meant by convection?
movement of water (and solutes dissolved in it) across a semi-permeable membrane in response to a pressure gradient
Also known as “ULTRAFILTRATION”
How does haemodialysis promote the removal of water?
Sets up a pressure gradient where the blood is higher than the dialysate
What is the main function of the microfilaments in the dialysis equipment which acts as an external kidney?
The increase the surface area available for exchange of water
Dialysate runs upwards as blood runs downwards
Adsorption affects what component of blood?
- Plasma proteins and solutes bound to them
- Plasma proteins of low molecular weight stick to the membrane surface and are removed by membrane binding
High flux membranes adsorb protein-bound solutes better than low flux membranes. TRUE/FALSE?
TRUE
What is the difference between haemodialysis and haemodiafiltration?
HD uses diffusion
HDF uses convection
Longer treatment times = better efficiency in haemodialysis. TRUE/FALSE?
TRUE
What must patients be warned if they choose to decrease their dialysis time?
Increased risk of death - 1% for every 30 mins less
How often is a patient usually on dialysis and for how long are they on the machine at a time?
4 hours
3 days a week
What restrictions do dialysis patients have to put on their diets?
Fluid (including foods which metabolise to H2O)
Salt
Potassium (avoid Banana, chocolate, potato, avocado)
Phosphate (or phosphate binders with meals)
What options are there for vascular access in dialysis?
Arteriovenous Fistula (AVF = Scribner Shunt) Tunnelled Catheter
What vein is a tunnelled catheter usually inserted into?
Internal jugular
What are the potential complications of a tunnelled catheter?
- infection
- blockage
- damage (stenosis/ thrombosis) to central veins can make future line insertion difficult
What are the main complications of arteriovenous fistulae?
- Require surgery
- Usually requires maturation of 6 – 12 weeks before can be used
What sites are used to establish arteriovenous fistulae?
Radio-Cephalic (RC AVF)
Brachio-Cephalic (BC AVF)
Brachio-Basilic transposition (BB AVF)
What types of graft can be used in dialysis?
Arteriovenous graft
=> between Cephalic vein and Brachial artery
HeRO Graft (Hemodialysis Reliable Outflow Graft) => either into Right Atrium OR Left subclavian
What can potentially go wrong in dialysis?
- Hypotension (can mimic cardiac arrest)
- Haemorrhage
- Loss of vascular access
- Arrhythmia /Cardiac arrest
Why does dialysis cause hypotension and myocardial stunning?
Removing large volumes of H20 3x per week
rather than continuously with normal kidneys
=> Leads to under-filling of the intravascular space and low BP
How does peritoneal dialysis work?
Solute removal by diffusion across the peritoneal membrane
Water removal by osmosis
- driven by high glucose concentration in dialysate fluid
How often does Continuous Ambulatory Peritoneal dialysis need changing?
4 x 2L bag exchanges per day
PD dialysate drained then fresh bag instilled
Takes 20-30 mins to exchange
How often is Automated Peritoneal Dialysis changed?
1 bag of fluid stays in all day
Overnight APD machine controls fluid drainage in and out for ~ 9-10 hours per night
What are the main complication of peritoneal dialysis?
Peritoneal
Exit site infection
Peritoneal membrane failure
Hernias
What blood tests would prompt starting dialysis?
- Resistant hyperkalaemia
- eGFR < 7 ml/min
- Urea > 40 mmol/L
- Unresponsive metabolic acidosis
How long should the first session of dialysis last in order to build up to the 4 hours?
90-120 minutes
What is Disequilibrium syndrome?
- Too-rapid a correction of uraemic toxin levels
- Cerebral oedema
- possible confusion
- seizures
- occasionally death
How long do patients need to train to administer peritoneal dialysis ?
3-6 weeks after PD catheter insertion
For what reasons may dialysis be withdrawn?
- Haemodynamic instability
- Progressive dementia (pull out catheter etc)
- Inability to remain on therapy for full duration due to agitation
- Cardiovascular event
- Terminal cancer
