Dialysis Flashcards
What is diffusion in dialysis?
Movement of solutes from a high to low concentration
Gradient will equalize to form an equilibrium
What is dialysis used for?
Allows removal of toxins that build up in CKD:
Urea
Potassium
Sodium
Allows the infusion of bicarbonate and calcium
What blood flow rate is needed for haemodialysis?
300-350 mls/min
What is commonly included in dialysate?
Pure water Na 138 HCO3 38 K 2-4 Glucose 5
What is convection?
Movement of water and all solutes dissolved in it across a semi-permeable membrane in response to a pressure gradient
What is adsorption concerned with?
Plasma proteins and any solutes bound to them
Plasma proteins stick to the membrane surface and are removed by membrane binding
High flux membranes adsorb protein-bound solutes better than low flux membranes
What mechanisms does hemodiafiltration rely on?
Increasingly convective
The greater the convective force, the greater will be the generated volume of pressure-driven ultrafiltrate
Large volumes of ultrafiltrate add to solute drag
What affects the convective transport of a molecule across a membrane?
Water flux (rate and volume) Membrane pore size (big or little holes) Pressure difference (hydrostatic pressure) Viscosity of hte fluid Size, shape and electrical charge
What is the difference between haemodialysis and hemodiafiltration?
Replacement of extra-convective ultrafiltrate throughout the dialysis period (minus any intended ultrafiltration volume)
As this replacement fluid must be given back directly to the patients circulation, the composition and purity of this fluid is pivotal
What restrictions does dialysis put on the patient?
Fluid - if anurinc needs to be 1litre per day (including food based fluid)
Salt - low salt diet to reduce thirst and help fluid balance
Low potassium diet
Low phosphate diet
What foods contain high levels of potassium?
Banana
Chocolate
Potato
Avocado
Where is a tunneled venous catheter commonly inserted into?
Internal jugular vein
What will commonly infect lines?
Staph aureus
Where can s. aureau seed?
Endocarditis
Discitis
Death
What is the treatment for line infections?
Vancomycin +/- gentamicin
What is the gold standard for dialysis vascular access?
Fistula - artery and vein surgically connected - venous part will develop to create an enlarged, thick walled vessel called an arteriovenous fistula
Where are common sites for fistulas?
Radio-cephalic
Brachio-cephalic
Brachio-basilic transposition
What can go wrong with dialysis?
Hypotension Haemorrhage Loss of vascular access Arrhythmia Cardiac arrest
How does peritoneal dialysis work?
Solute removal via diffusion of solutes across the peritoneal membrane
Water removal via osmosis driven by a high glucose concentration in dialysate fluid
What infections can complicated peritoneal dialysis?
Peritonitis or exit site infection
Contamination: staphylococci, streptococci, diphtheroids
Gut bacteria translocation: e.coli, klebsiella
What is the management of peritoneal dialysis?
Culture PD fluid
Intra-peritoneal antibiotics (gram positive, gram negative)
May need catheter removal
What is peritoneal membrane failure?
Inability to remove enough water - fluid overloaded
Inability to remove solutes
Requires switch to HD
When should dialysis be started?
Resistant hyperkalaemia
eGFR <7 ml/min
Urea >40 mmol/L
Unresponsive metabolic acidosis
What symptoms should prompt you to start dialysis?
Nausea Anorexia Vomiting Profound fatigue Itch Unresponsive fluid overload
How is dialysis started?
1st session 90-120 in
Subsequent sessions up to 4 hours
What can occur with a too rapid correction of uraemic toxin levels?
Disequilibrium syndrome: cerebral oedema, confusion, seizures and death
Why will dialysis be drawn from a patient?
Haemodynamic instability
Progressive dementia
Inability to remain on therapy for full duration
CV event
Terminal cancer
Increasing fragility and inability to cope at home
