Dialysis Flashcards
What are the 3 main transport mechanisms at play in dialysis?
Diffusion
Convection
Adsorption
What is diffusion?
Diffusion is the process by which particles, atoms or molecules move from an area of high concentration to an area of low concentration across a semi-permeable membrane
What factors can influence diffusion?
The concentration gradient and molecular weight of the solute both influence this process
What is ultrafiltration?
The movement of water and all solutes in it across a semi-permeable membrane in response to a pressure gradient
What is convection?
The movement of solutes through a membrane in response to the movement of fluids in ultrafiltration
What is adsorption?
Plasma proteins (Especially of low molecular weight), stick to the membrane surface and are removed by membrane binding
What type of membrane is best at allowing adsorption?
High flex membranes adsorb protein-bound solutes better than low flux membranes
What is dialysis?
A process that allows the removal of uraemic toxins and small solutes which build up in end-stage kidney disease
What are some uraemic toxins removed in dialysis?
- Urea and creatinine
- Potassium
- Sodium
What is dialysate?
A solution used to filter uraemic toxins
What is contained in the dialysate?
- Sodium
- Potassium
- Calcium
- Bicarbonate
- Magnesium
- Chloride
- Glucose
Why is the dialysate composition so important?
It prevents excessive losses of small solutes, many of which would be selectively reabsorbed by the native kidney
What are the 3 types of dialysis?
- Haemodialysis (HD)
- Haemodiafiltration (HDF)
- Peritoneal dialysis (PD)
What is the main transport mechanism of haemodialysis (HD)?
Diffusion
Small amount of convection and adsoprtion
What are the 9 stages of haemodialysis?
- Vascular access gained
- Blood removed (Rate 300-350mls/min)
- Arterial pressure monitored
- Heparin pump (Prevents clotting)
- Dialyzer inflow pressure monitoring
- Dialyzer (Contains dialysate)
- Venous pressure monitored
- Air trap and air detection
- Return of blood to the body
What are the 4 methods of gaining vascular access in dialysis?
- Arteriovenous fistula
- Arteriovenous graft
- Tunnelled central venous catheter
- Temporary venous catheter
What is the main transport mechanism of haemodiafiltration?
Convection (Ultrafiltration)
Describe the process of haemodiafiltration
Large volumes of ultra-filtrate add enormously to the solute drag, especially for larger “Middle molecules”
The greater the convective force, the greater will be the generated volume of the pressure-driven ultra-filtrate
There is still diffusion down engineered concentration gradients
As there is a large amount of fluid and solutes removed from the blood in HDF, then this fluid volume needs to be replaced
Replacement of extra-convective ultra-filtrate throughout the dialysis period is the key difference between HD and HDF
Ultrapure replacement fluid - As this replacement fluid must be given back directly to the patient’s circulation, the purity of this replacement fluid is pivotal
What are the positives of HDF?
HDF has been reported to offer a smoother, less symptomatic treatment than HD, enhances recovery time, improves survival and can be achieved at a similar cost to HD
What is the minimum prescription of HD and HDF?
3.5-4 hours per session, 3 times per week
What dietary changes are required in dialysis?
- ~1L fluid and food-water intake
- Low salt diet to reduce thirst
- Low potassium diet (Avoid bananas, chocolate, potatoes and avocado, etc.)
- Low phosphate diet (May require phosphate binders with meals)
What is involved in tunnelled central venous catheter (TCVC)
This is a catheter inserted into a large vein, typically the internal jugular vein
What are the pro’s of TCVC?
- Easy to insert
- Can be used immediately
What are some cons of TCVC?
- Higher risk of infection
- Most common staph aureus (Endocarditis and discitis)
- Blood flow issues - Clots and fibrin sheath
- Damage (Stenosis and thrombosis)
What is the gold standard for vascular access in dialysis?
Arteriovenous fistula (AVF)
What is involved in arteriovenous fistula?
It involves the surgical connection of an artery and vein
The venous part will develop to create a thick walled vessel called an arteriovenous fistula
What is an important not about arteriovenous fistula?
Don’t take any bloods or put needles in that arm: Protect the fistula!!
What are some common sites of arteriovenous fistula?
- Radio-cephalic
- Brachio-cephalic
- Brachio-basilic transposition
What are some pro’s of AVF?
- Good blood flow
- Less likely to cause infection
What are some cons of AVF?
- Requires surgery
- Usually requires maturation of 6-12 weeks before use
- Can limit blood flow to distal arm/hand (Steal syndrome)
- Can thrombose, stenose or rupture (Rare)
What is meant by sharp and dull needling in AVF?
Sharp needling is done by nurses with dialysis and requires formation of 3 holes into the AVF
This forms 3 tracts
Dull needling can then be practised by the patient with home dialysis where they insert a dull needle into these tracts which only slightly scab over
What is involved in an arteriovenous graft (AVG)
What is involved in haemodialysis reliable outflow graft (HeRO graft)
What are some complications of vascular access in dialysis?
- Hypotension
- Haemorrhage
- Loss of vascular access (Thrombosis, stenosis, infection)
- Arrhythmia
- Cardiac arrest
What is peritoneal dialysis?
This is a form of dialysis involving the peritoneal cavity
What is involved in PD?
Dialysate is pumped into the peritoneal cavity, allowing diffusion of solutes across the peritoneal membrane and osmosis of water, driven by the high glucose concentration in the dialysate
The waste fluid is then pumped out
Dialysate drainage in and out is controlled by the APD machine overnight
What are the 2 main types of peritoneal dialysis?
- Continuous ambulatory peritoneal dialysis (CAPD)
- Automated peritoneal dialysis (APD)
What is involved in CAPD?
CAPD requires 4 x 2L bag exchanges per day, with 20-30 minutes per exchange
What is involved in APD?
APD takes around 9-10 hours per night, with 1 bag of fluid staying in all day
What are some complications of PD?
- Infection (Peritonitis)
- Peritoneal membrane failure
- Hernias
How is peritonitis in PD managed?
culturing the PD fluid, giving intra-peritoneal antibiotics and possible catheter removal
What can arise from peritoneal membrane failure?
Peritoneal membrane failure can cause failure of movement of water or solutes
Inability to remove enough water can lead to fluid overload
Inability to remove enough solute can cause uraemia
What are some blood tests results that require dialysis?
- Resistant hyperkalaemia
- eGFR < 7ml/min
- Urea > 40mmol/L
- Unresponsive metabolic acidosis
What are some symptoms in CKD that may require dialysis?
- Nausea
- Anorexia
- Vomiting
- Profound fatigue
- Itch
- Unresponsive fluid overload
How is HD started?
gradually, with the 1st session lasting 90-120 minutes and working up to 4 hours
What is disequilibrium syndrome?
A syndrome occurring when correction of uraemic toxin levels happens too rapid, causing mass movement of water between internal and external fluid compartments in the body
What are some symptoms of disequilibrium syndrome?
- Cerebral oedema
- Confusion
- Seizures
- Death
How is PD started?
PD is started with training with smaller fill volumes around 3-6 weeks after PD catheter insertion
Fill volumes are then increased in size to 2-2.5L
What are some medical reasons for dialysis withdrawal
- Haemodynamic instability
- Progressive dementia
- Agitation
- Cardiovascular event
- Terminal cancer
- Increasing frailty
Who is involved in withdrawing from dialysis?
This is an active decision made by the patient and treating team and requires palliative care involvement
