Dialysis Flashcards
what are the three concepts of dialysis
diffusion- movement of solutes along con gradient (high to low) across semi permeable membrane to equalise gradient
convection- movement of water (and all dissolved solutes) across a semi permeable membrane in resposne to a pressure gradient- convective solute drag
adsoprtion- plasma proteins (and bound solutes) stick to the membrane surface and are removed by binding
what toxins are removed in dialysis
urea
potassium
sodium
what is infused into the blood dialysis
(in pure H20)
bicarbonate
(also Na
K
glucose)
what is the normal blood flow rate
300-350 mls/ miin
how does haemodialysis (HD) work
blood filtered though filaments with semi permeable membranes
what is ultrafiltration
convection- removal of water from the blood into the dialysate
what membranes are used for adsorption
high flux (absorb protein bound solutes better)
what is haemodiafiltration
convective forces causing ultrafiltration then replacing it
is haemodialysis diffusion or convection
diffusion
what do you replace ultrafiltrate with
ultra pure fluid (ri-infusate)
what affects haemodiafiltration
Water flux (rate and volume)
Membrane pore size
The pressure difference (hydrostatic pressure) applied to and across the membrane
Viscosity of the fluid
The size, shape and electrical charge of each molecule
what amount of fluid is high volume HDF (haemodiafiltrate)
> 20 litres in 24 hrs
what are the benefits of HDF
offer a smoother, less symptomatic treatment than HD
enhances recovery time
improves survival
similar cost to conventional HD
how efficient is dialysis
not- long treatment times
what restrictions must the patient on dialysis follow
fluid- if anuric 1 litre/ day (inc food)
low salt
low potassium
low phosphate (take phosphate binders with meals)
what are the vascular access options in dialysis
tunneled venous catheter (usually into IJV- easy to insert, high risk of infection, can cause vascular damage)
fistula (gold standard) (artery and vein surgically connected - venous part develops thich walled arteriovenous fistula ) (less likely yo get infections, requires surgery, 6-12 weeks before use, can limit blood flow to distal arm (steal syndrome))
hemodialysis reliable outflow graft (2nd best)
what infections are seen in tunneled venous catherters
s aureus (endocarditis, discitis, death)
where can you get a fistula created
radio-cephalic
brachio-cephalic
brachio-cephalic transposition
what can go wrong in dialysis
hypotension
haemorrhage (ruptured AVF)- life threatening
loss of vascular access (thrombosis, stenosis, infection)
arrhythmia (electrolyte imbalance, myocardial ischaemia)
cardiac arrest
what causes intra-dialytic hypotension
aka ‘myocardial shunning’
removal of large volumes of water
under filling of the intravascular space and low BP
how does peritoneal dialysis work
dialysate fluid line and catheter inserted into peritoneum (peritoneal fluid)
Solute removal by diffusion of solutes across the peritoneal membrane (semi-permeable membrane) (from blood into peritoneum)
Water removal by osmosis (water moving to equalize a concentration gradient) - driven by high glucose concentration in dialysate fluid
PD dialysate drained by catheter
can also be automated where drained by a APD machine overnight
what can go wrong in peritoneal dialysis
Infection
Peritonitis or exit site infection (contamination, gut bacteria translocation)
peritoneal membrane failure (fluid overload/ uraemic (cant remove solutes))
hernias (increased abdo pressure)
what is the management for a PD infection
Culture PD Fluid
Intra-peritoneal antibiotics
Gram positive
Gram Negative
May need catheter removal
when do you start dialysis
based on blood tests:
Resistant hyperkalaemia
eGFR < 7 ml/min
Urea > 40 mmol/L
Unresponsive metabolic acidosis
based on symptoms: Nausea Anorexia Vomiting Profound fatigue Itch Unresponsive fluid overload
why do you have to build up to a four hr session in HD (start at 90-120 mins)
Too-rapid a correction of uraemic toxin levels can lead to Disequilibrium syndrome:
Cerebral oedema and possible confusion, seizures and occasionally death
how do you start
PD
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
why should some people not get dialysis
In ESRD, as age increases, survival with RRT decreases
Patients > 75, with numerous co-morbidities, are expected to have similar number of ‘hospital free’ days whether starting HD or not
Quality of life Vs Quantity of life (patient to make an informed choice)
RRT is expensive and healthcare budget is not limitless
what medical reasons might you withdraw from dialysis
Haemodynamic instability Progressive dementia Inability to remain on therapy for full duration due to agitation Cardiovascular event Terminal cancer
what social reasons might you withdraw from dialysis
Increasing fraility and inability to cope at home
what is the best form of renal replacement therapy
transplant- dialysis stopgap before this in those who are suitable
can you get dialysis at home
yes
how does dialysis affect QoL
badly
