Dialysis Flashcards
what are the 3 main concepts in dialysis
diffusion
convection
adsorption
what is diffusion
movement of solutes from high to low concentration gradient to equalise the concentrations
what does diffusion allow in dialysis
removal of toxins and water products
(urea, K and Na)
infusion of bicarbonate
what happens when the blood enters the dialysis machine
it looses K Urea and Na through a semi permeable membrane into the dialysis fluid
it gains bicarbonate from the dialysis fluid into the blood
what is in the dialysis fluid (dialysate)
pure H20 Na HCO3 K Glucose
how does haemodialysis get rid of water
through convection
water (and solutes dissolved in it) are moved across the semipermeable membrane by a PRESSURE gradient
what is ultrafiltration
the removal of water from the blood via a pressure gradient
there is negative pressure in the dialysate which pulls the water out
what happens to plasma proteins during haemodialysis
they often stick to the membrane surface and get removed by membrane binding
what is the difference between haemodialysis and haemodiafiltration
haemodyalisis is mainly diffusive
haemodiafiltration is mainly convective (uses pressure)
what is the effect of the ultra filtrate in haemodiafiltration
high convective force produces lots of ultra filtrate
this sets up a solute - drag which pulls out larger ‘middle molecules’
there is diffusion down engineered concentration gradients
what things affects the efficiency of the convective transport in haemodiafiltration
water flux
membrane pore size
pressure difference across membrane (hydrostatic)
viscosity of the fluid
size, shape and electrical charge of the molecules
what is the key difference between HD and HDF
in HDF replacement fluid is given to the patient to replace the loads of ultra filtrate taken out
High volume HDF has replacement volumes of >20 litres
what are the benefits of HDF
- smoother, less symptomatic treatment
- enhances recovery time
- improves survival
what makes dialysis more efficient
longer treatment times
what is the minimum HD/HDF prescription
4 hours
3 times a week
what happens when you decrease dialysis time by 30 mins
it gives a 1% increased risk of death
what restrictions does dialysis put on the patients diet
- Must reduce fluid to 1 L per day
- Low salt diet (helps reduce thirst and helps fluid balance)
- Low potassium diet
- Low phosphate diet
what are the options for gaining vascular access for dialysis
Tunneled venous catheter
Fistula
Atriovenous graft
HeRO graft
what is a tunnelled venous catheter
a catheter inserted into a large vein - usually internal jugular
what are the pros of a tunnelled venous catheter
easy to insert
can be used immediately
what are the cons of a tunnelled venous catheter
- high risk of infection
- can become blocked
- can cause damage to veins making line insertion difficult in future
what infections do you tend to get with tunnelled venous catheters
STAPH AUREUS
leads to
- endocarditis
- discitis
- death
treatment for tunnelled venous catheter infection
antibiotics
-vancomycin +/- gentamicin as empirical until cultures are back
what is a arteriovenous fistula
the gold standard for vascular access
artery and vein surgically connected to form a thick walled enlarged vessel
what are the pros of an arteriovenous fistula
good blood flow
less likely to cause infection
cons of an arteriovenous fistula
required surgery
needs maturation of 6-12 weeks before use
can limit blood flow to distal arm
can thrombose or pentose
what is an arteriovenous graft
a graft that connects an artery to a vein
what is a HeRO graft
for complex access
long graft with venous component on one side and arterial much further down
canulation area is in the middle of the graft
complications of dialysis
hypotension haemorrhage (ruptured fistula) loss of vascular access arrhythmia cardiac arrest
what is peritoneal dialysis
then the solute is removed by diffusion across the peritoneal membrane
water removed by osmosis driven by a high glucose concentration in the dialysate fluid
what is continuous ambulatory peritoneal dialysis
dialysis that can be done at home
4x2L bag exchanges per day
peritoneal dialysate is drained and a fresh back is installed
takes 20-30 mins per exchange
what is automated peritoneal dialysis
1 bag of fluid stays in outside the peritoneum all day
an overnight ADP machine controlled fluid drainage in and out for 9-10 hours per night
what are the complications of peritoneal dialysis
infection
-peritonitis or exit site infection
Peritoneal membrane failure
Hernia
what bacterial tend to cause infection in peritoneal dialysis
contamination from:
staph
strep
diptheriods
gut commensals:
e.coli
klebseilla
how do you manage infection in peritoneal dialysis
culture peritoneal dialysate
intraperitoneal antibiotics
may need catheter removal (if entry site)
what is peritoneal membrane failure
inability of the membrane to remove enough water due to fluid overload
inability to remove enough solutes
needs switch to HD
how does PD cause hernias
due to the increased intra-abdominal pressure
required hernia repair and smaller fill volumes
when should you star dialysis based on bloods
resistant hyperkalaemia
eGFR <7
urea >40
Uresponsive metabolic acidosis
when should you start dialysis based on symptoms
if there is:
nausea vomiting anorexia profound fatigue itch unresponsive fluid overload
how do you start haemodialysis
gradual build up
first session lasts 90-120 mins and build up to 4 hours
what happens if uraemic. toxin levels are corrected too rapidly
disequilibrium syndrome
- cerebral oedema
- confusion
- seizures
- death (occasionally)
when should you stop dialysis
- haemodynamic instability
- progressive dementia
- Inability to remain on therapy for full duration due to agitation
- cardiovascular event
- terminal cancer
unable to cope at home - increasing frailty
you then need palliative care involvement
