Dialysis Flashcards
What is dialysis used for? (2)
- Removing toxins from the blood which build up in end stage kidney disease (ESKD) (blood to dialysate)
- Allowing the infusion of bicarbonate into the blood (dialysate to blood)
Dialysis is considered to be a ‘stop-gap’ until transplantation. T/F?
True
for patients who are suitable for transplant
By what 3 mechanisms are molecules exchanged between the blood and the dialysate?
Diffusion
Convection
Adsorption
Describe how diffusion works when referring to dialysis
Molecules move from the solution with their higher concentration to the solution with their lower concentration gradient across the semi-permeable membrane of filaments within the dialyser
What 3 factors affect solute diffusion between the blood and the dialysate?
- Solute concentration gradient
- Molecular weight of solute
- Permeability of the membrane of the filaments in the dialysate
Ultrafiltration is important for convection. What is ultrafiltration?
Ultrafiltration is the movement of water from the blood to the dialysate by setting up a pressure gradient for water i.e., water pressure is -ve in the dialysate so that water moves into it from the blood
Describe how convection works when referring to dialysis, making reference to ultrafiltration
Water is removed from the blood by ultrafiltration, taking it across the semi-permeable membrane and into the dialysate
Convection refers to the removal of solutes (e.g., urea, K+, Na+) dissolved in the water as it moves out in the ultrafiltrate along the pressure gradient of water
What 3 factors affect solute movement between the blood and the dialysate by convection?
- Water volume and flow rate
- Water pressure gradient (hydrostatic pressure)
- Permeability of the filament membranes
- Molecular size, shape, and charge of the solute
- Viscosity of the fluid within the membrane pores
Describe how adsorption works when referring to dialysis
Plasma proteins, and any solutes that are bound to them, can bind to specific polymers in the membrane of the dialysis filaments
Therefore, membrane binding removes these protein-bound solutes from the bloodstream
What is meant by a ‘high-flux membrane’?
A synthetic dialysis membrane which has a high ultrafiltration coefficient
Are protein-bound solutes adsorbed better by high or low-flux membranes?
High-flux membranes
What are the 3 main types of dialysis?
Haemodialysis (HD)
Haemodiafiltration (HDF)
Peritoneal dialysis (PD)
Which of the following mechanisms does haemodialysis rely most heavily on?
Diffusion
Convection
Adsorption
Diffusion
In haemodialysis, what substances travel from…
-The patient’s blood to the dialysate
-The dialysate to the patient’s blood
?
Patient’s blood to the dialysate:
- Urea
- Creatinine
- Na+
- K+
- Other toxins
Dialysate to the patient’s blood:
- HCO3-
- Glucose
What is the standard flow rate of dialysate in haemodialysis?
Therefore, how much dialysate is required in a 4 hr treatment cycle?
500ml/min
120L in a 4 hr treatment
Different dialysate concentrations are available. They differ mainly in their concentration of…? Why?
K+ ions
Depending on patients K+ levels and risk of hyperkalaemia
Which of the following mechanisms does haemodiafiltration rely most heavily on?
Diffusion
Convection
Adsorption
Convection
What is the main difference between haemodialysis and haemodiafiltration?
In haemodialysis, solutes are removed from the patients blood by diffusion, down the concentration gradient of the solute
In haemodifiltration, solutes and water are removed from the patients blood by convection, down the pressure gradient of water created by the ultrafiltrate
Haemodiafiltration requires the delivery of ‘re-infusate’ into the patient’s bloodstream. What is re-infusate and why is it required?
Re-infusate = a replacement fluid which is delivered directly back into the circulation of a patient on haemodiafiltration
It is required because a large volume of water is removed from the patient’s bloodstream to drive ultrafiltration (convective water-solute drag)
High volume haemodiafiltration is defined as HDF requiring a re-infusate volume of ? litres per HDF session
> 21
this means that >21 litres of body fluid have been removed from the patient and replaced by infusate
What are the advantages of using haemodiafiltration over haemodialysis? (5)
- The solute drag which comes with ultrafiltration allows more solute to be removed from the blood, as the pressure gradient can pull larger solute molecules from the bloodstream into the dialysate
- Patients experience less symptoms with treatment than when on HD
- Recovery time is quicker
- Chance of survival is improved
- Benefits are achieved at a similar cost to HD
What is the ‘basic’/’minimum’ prescription for haemodialysis/haemodiafiltration treatment?
4 hour session 3x per week
Give a pro and a con for increasing dialysis treatment regime to > 4 hours 3x per week?
Pro: Treatment is more efficient (as real kidneys function 24/7) and therefore survival may be improved
Con: Quality of life is negatively impacted
For every 30 minutes less than the 4 hr minimum treatment recommendation for dialysis, by what % does risk of death increase?
1% for every 30 minutes less
List 4 restrictions that dialysis puts on the patient, due to the fact that they have non-functioning kidneys for the majority of the time?
Restrict fluid intake to ~1L per day (including food-based fluid e.g., fruit and veg are 100% water)
Restrict salt intake to <2.3g daily to reduce thirst and help with fluid balance
Restrict K+ intake to prevent hyperkalaemia (K+ found in bananas, chocolate, potato, avocado), can also reduce K+ concentration in dialysate
Restrict phosphate intake, phosphate binders can be taken with meals if phosphate remains high
Why does vascular access for HD/HDF need to be from a large vessel?
Because a blood flow rate of ~300-350 mls/min is required and this cannot be achieved by entering small vessels
What are the 4 main methods of vascular access for HD/HDF?
Arteriovenous Fistula (AVF)
Arteriovenous Graft (AVG)
Tunnelled Central Venous Catheter (TCVC)
Temporary Venous Catheter (VasCath)
What is the gold-standard method for dialysis vascular access?
Arteriovenous fistula (AVF)
What is an arteriovenous fistula?
An artery and vein are surgically connected, the venous part then develops to create an enlarged, thick-walled vessel called an AVF
What are the 3 most common sites for an AVF?
Radio-cephalic fistula at the wrist (radial artery + cephalic vein)
Brachio-cephalic fistula at the elbow (brachial artery + cephalic vein)
Brachio-basilic transposition fistula at the elbow (brachial artery + basilic vein)
What are the pros of AVF? (2)
- Allows for good blood flow
- Less likely to cause infection as no foreign bodies are inserted
What are the cons of AVF? (5)
- Surgery is required to establish the fistula
- Needs to be established 6-12 weeks before dialysis started to allow for maturation time
- Risk of limiting blood flow to the distal arm - ‘steal syndrome’
- Risk of thrombosis or stenosis
- Risk of pseudoaneurysm formation or fistula rupture
What is an arteriovenous graft?
When is it used?
The use of synthetic graft material to connect an artery and a vein - it is this graft material that is needled for dialysis
It is less common than AVF and is used if AVF is not an option
What is a HeRO graft? (haemodialysis reliable outflow graft)
A haemodialysis graft which involves connecting an artery to a vein which drains directly into the SVC via a titanium graft
When may a HeRO graft be used?
To avoid thrombosed or stenosed veins which are obstructing blood flow back to the heart
What is a Tunnelled Central Venous Catheter (TCVC)?
A catheter which is inserted directly into a large vein, most commonly the internal jugular vein
(femoral veins or IVC less commonly)
What are the pros of using a tunnelled central venous catheter (TCVC)? (2)
- Easy to insert (usually)
- Can be used immediately so good if required urgently e.g., in AKI
What are the cons of using a tunnelled central venous catheter (TCVC)? (3)
- High risk of infection
- Can become blocked
- Can damage central veins, making future line insertion difficult e.g., thrombosis, stenosis
What are the most common infections caused by TCVCs?
- Staph aureus bacterial infection
- Endocarditis if septic emboli occur
- Discitis (IV discs) if septic emboli occur
What is the treatment for a TCVC infection?
Vancomycin + gentamicin (for gram +ve and gram -ve cover)
Line removal or exchange
List 5 complications of dialysis and briefly describe them
- Hypotension / ‘myocardial stunning’ (greatly reduced CO) due to removal of large volumes of H2O without adequate replacement
- Haemorrhage due to rupture of an AVF
- Loss of vascular access due to thrombosis, stenosis, or infection
- Arrhythmia due to electrolyte imbalance/myocardial ischaemia
- Cardiac arrest if the treatment is just too aggressive for the body to take
What is peritoneal dialysis?
Solute exchange between the blood and dialysate by diffusion of solutes across the peritoneal membrane
Describe how peritoneal dialysis is carried out
- A catheter is inserted into the abdomen just below the umbilicus
- Sterile dialysate is infused into the peritoneal cavity
- Substances are exchanged between the blood capillaries and the dialysate across the semi-permeable peritoneal membrane
- The waste fluid is then removed from the peritoneal cavity
Why do you need to be cautious with peritoneal dialysis in diabetics?
A small amount of glucose enters the bloodstream from the dialysate down its concentration gradient
What are the 2 types of peritoneal dialysis?
Continuous ambulatory PD (CAPD)
Automated PD (APD)
What are the differences between continuous ambulatory PD (CAPD) and automated PD (APD)?
CAPD:
- Dialysis carried out at regular intervals throughout the day
- 4x 2L bag exchanges per day, each for 20-30 minutes
APD:
- Dialysis carried out overnight by an automated machine
- Typically for 9-10 hours per night
- 1 bag of fluid stays in all day - the ‘day dwell’
What determines whether a patient receives continuous ambulatory PD (CAPD) or automated PD (APD)?
Patient choice
Peritoneal characteristics
What are the possible complications of peritoneal dialysis? (3)
Briefly describe them
- Infection (peritonitis or exit site infection), most commonly staph or strep infection or gut bacteria translocation e.g., E.coli
- Peritoneal membrane failure due to inability to handle fluid overload or uraemia
- Hernias due to increased intra-abdominal pressure from inflowing treatment, hernia must be repaired before treatment re-commenced
What are the indications for starting dialysis? Give 4 blood test indications and symptom indications
Blood tests:
- Resistant hyperkalaemia, esp. if >6 mmol/L
- eGFR <7 ml/min
- Urea >40 mmol/L
- Unresponsive metabolic acidosis
Symptoms of uraemia e.g., nausea, loss of appetite, vomiting, profound fatigue, itch, fluid overload unresponsive to diuretics
How is a patient gradually brought onto haemodialysis treatment?
- 1st session is ~1.5-2 hrs
- Subsequent sessions build up to 4 hours after 3-4 sessions
What is disequilibrium syndrome?
Where too-rapid reduction in uraemic toxin levels leads to cerebral oedema, confusion, seizures, and occassionally death
How is a patient gradually brought onto peritoneal dialysis treatment?
- Patient is trained how to use PD in the 3-6 weeks of healing following insertion of their catheter
- Gradually build fill volumes up to 2-2.5L
Dialysis patients report a similar QoL as the general population. T/F?
False
Dialysis patients report a lower QoL than the general population and generally suffer a heavy burden of symptoms
What symptoms are often experienced by patients on dialysis?
Pain
Itch (due to uraemia)
Depression
Loss of appetite
In what circumstance may a patient with ESRD choose not to receive dialysis?
Patients >75 with multiple co-morbidities are expected to have a similar number of hospital free days regardless of whether they start HD or not
Therefore, the patient should make an informed choice about the quality vs quantity of life they want to live (i.e., HD may not give them any longer to live but will significantly impact their quality of life)
What help is available for the ~20% of ESRD patients who choose not to receive dialysis?
A separate supportive clinic is available in the community
Home HD is less common than in-centre HD. When might a patient get home HD and what are the benefits of it?
May be preferred in patients who are young, physically fitter, and have a carer to help at home
Benefits: offers the patient more freedom as shorter sessions can be carried out for more times per week
Give 5 reasons why a patient, their treating team, and their family may decide to withdraw dialysis treatment?
- Haemodynamic instability
- Progressive dementia making treatment distressing
- CV event
- Terminal cancer
- Increasing frailty and inability to cope at home
Why are palliative care involved in withdrawal from dialysis?
Life expectancy is days - weeks once dialysis stopped
