Dialysis Flashcards
What are the different types of dialysis?
Haemodialysis
Haemofiltration
Peritoneal Dialysis
what is haemodialysis?
Blood is passed over a semi-permeable membrane against dialysis fluid flowing in the opposite direction
what is the mechanism of haemodialysis?
Primarily Diffusive
blood is always meeting a less-concentrated solution and diffusion of small solutes occurs down the concentration gradient
how is excess fluid cleared in haemodialysis?
Ultrafiltration creates a negative transmembrane pressure and is used to clear excess fluid
Diffusion allows the movement of which molecules in haemodialysis?
K, Ur, Na move from blood to dialysis fluid
Pure H2O, Na 138, HCO3 38, K 2-4, Glucose 5 moves from dialysis fluid into the blood
what does convection allow in haemodialysis?
ULTRAFILTRATION
Negative pressure gradient = 100-200mmHG
what is convection?
The movement of water (and all solutes dissolved in it- convective solute drag) across a semi-permeable membrane in response to a pressure gradient
what is adsorption in haemodialysis?
Plasma proteins (especially those 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
what are the indications for haemodialysis?
uraemic pericarditis, refractory hyperkalaemia, pulmonary oedema, sever metabolic acidosis
what are the problems with haemodialysis?
: Disequilibrium syndrome, hypotension, time consuming, access problems (arteriovenous fistula; thrombosis, stenosis, steal syndrome; tunnelled venous access line: infection, blockage, recirculation of blood
what is hemofiltration?
Blood if filtered across is highly permeable membrane, allowing movement of large and small solutes by convection at almost the same rate. The ultrafiltrate is replaced with an equal volume of fluid, so there is less haemodynamic instability.
when is hemofiltration used?
critically ill patients
what is the link between convection force and pressure?
The greater the convective force, the greater will be the generated volume of the pressure-driven ‘ultrafiltrate’
Large volumes of ultrafiltrate add enormously to solute drag - especially for the larger “middle molecule” solute classes
what can impact on the efficiency of convective transport?
wtare flux, membrane pore size, pressure difference, viscosity of the fluid, size, shape and electrical charge
what is the benefit to haemofiltration?
offers a smoother, less symptomatic treatment than HD; enhances recovery time; improves survival, achievable at a similar cost to conventional HD
why is hemofiltration impractical long term?
takes much longer to achieve the same clearance
how long are dialysis treatments?
– 4 hours
– 3 times per week
wat is the link between dialysis time and survival?
Longer treatment times = better efficiency
what are the restrictions with patients on dialysis?
- Fluid - ~ 1litre per day
- Salt - Low salt diet
- Potassium - Low potassium diet
- Phosphate - Low phosphate diet,
what is the vascular access required for dialysis?
Fistula = gold standard
Tunnelled Venous Catheter
what is a fistula?
Join an artery and a vein to make an enlarged, thick walled vessel called an Arteriovenous Fistula (AVF)
what are the pros to fistulas?
Good blood flow, Less likely to cause infection
what are the cons to fistulas?
- requires surgery, Requires maturation of 6 – 12 weeks before can be used, Can limit blood flow to distal arm “steal”, Can thrombose or stenose
what is a tunnelled venous catheter?
A catheter inserted into a large vein, typically; the Internal Jugular or Femoral vein
what are the pros to tunnelled venous catheters?
Easy to insert (usually), Can be used immediately
what are the cons to tunnelled venous catheters?
High risk of infection, Can become blocked, Can cause damage (stenosis/ thrombosis) to central veins making future line insertion difficult
what infections are associated with tunneled venous cathether?
Staph Aureus (endocarditis, discitis, death – treat with vancomycin + gentamicin and remove line or exchange)
what are the complications to dialysis?
- Hypotension
- Blood leaks
- Loss of vascular access
- Hyperkalaemia and cardiac arrest
- Protein-calorie manutrion
- Renal bone disease
- Malgniancy
- Amyloid accumulation
how does hypotension occur in dialysis?
Myocardial stunning’ on dialysis
• Removal of 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 can it be determined when to start dialysis?
based on symptoms
based on blood results
which blood results indicate to start dialysis?
: Resistant hyperkalaemia, eGFR <5, Urea >40, Unresponsive acidaemia
which symptoms indicate to start dialysis?
Profound fatigue, Itch, Unresponsive fluid overload, Nausea, Anorexia, Vomiting
what are the problems peritoneal dialysis?
loss of membrane function over time
Peritonitis or exit site Infection
Peritoneal Membrane Failure
Hernia
what is peritoneal dialysis?
Uses the peritoneum as a semi-permeable membrane. A Tenckhoff catheter is inserted into the peritoneal cavity and fluid infused, allowing solutes to diffuse slowly across
how is ultrafiltration achieved in peritoneal dialysis?
by adding osmotic agents such as glucose to the fluid (i.e. water removal by osmosis)
what are the benefits to peritoneal dialysis?
simple to perform, can be carried out continuously and at home
what are the two types of peritoneal dialysis?
- CAPD (continuous peritoneal dialysis)
* APD (automated peritoneal dialysis)
what are the features of CAPD?
o 4 x 2L bag exchanges per day
o PD dialysate drained then fresh bag instilled
o 20-30 mins per exchange
what are the features of APD?
o 1 bag of fluid stays in all day – The ‘day dwell’
o Overnight APD machine controls fluid drainage in and out for ~ 9-10 hours per night
how is haemodialysis sessions built up?
– 1st session 90-120 minutes
– Subsequent sessions build up to 4 hours
– Start GFR is usually 8-10mL/min
what are the symptoms of disequilibrium syndrome?
Cerebral oedema and seizures
how is peritoneal dialysis built up?
- Training (3-6 weeks after PD catheter insertion)
- Starts with smaller ‘fill volumes’
- Fill volumes increase in size to ~ 2.0-2.5L
- Regular clinic and nurse follow up
what are the reasons to withdraw dialysis?
Medical - PVD, Cerebrovascular disease, CVD, Cancer
Social Reasons
Palliative care
