Dialysis - North West Urology Registrar Group

Diffusion of solutes,
ultrafiltration of fluid
across a semi-permeable membrane.
1. Acidosis with pH<7 not responding to treatment
is an indication for dialysis.
2. Gastritis, hypothermia, and fits are signs of
3. CAPD involves one exchange of fluid a day.
4. Hypoglycaemia is a complication of peritoneal
5. An abdominal wall stoma is not a
contraindication to peritoneal dialysis.
Indications for dialysis
1. ARF
2. CRF
Indications in ARF
• Absolute indications:
– Uraemia
» (e.g. pericarditis, gastritis, hypothermia, fits or encephalopathy)
– Fluid overload
» leading to pulmonary oedema not resolving with diuretics
– Severe Hyperkalaemia
» (potassium > 6.5mmol/L) unresponsive to medical management
– Acidosis
» (pH < 7.0) not responding to treatment (eg. sodium bicarbonate)
• Relative indications:
– Serum sodium > 155mmol/L or < 120 mmol/L
– Severe renal failure (urea > 30 mmol/L, Creatinine > 500 micromol/L)
– Toxicity with drugs that can be dialysed
Indications in Chronic Renal Failure
• When to start dialysis is controversial (if no urgent indication)
• In general, GFR 10 mL/minute (15 mL/minute if diabetic)
• Before <6 ml/min regardless
• No evidence that starting dialysis earlier is of any benefit to patients
• Mortality rate and low quality of life VS complications of CRF
• NEJM. 2010;363(7):609-19
– RCT, 32 centres Australia / NZ, 828 adults
– Early (eGFR 10-15ml/min) vs Late (eGFR 5-7 ml/min)
– No significant difference in survival or clinical outcomes
• No RCTs comparing HD with HF but Cochrane Review in
2006 showed equivalence (Rabindranath, CD006258)
Principles of dialysis
Principles of dialysis
• Blood side – blood flows on one side
• Dialysis side – dialysate flows on other side
• The dialysate contains H2O,Na, K, Cl,HCO3, Mg, Ca,
• Dialyser unit with semi-permeable membranes.
– Bundles of capillary-like hollow fibres in cylindrical
– Blood flows through fibres, dialysate flows within
surrounding shell
• Vascular access - AV fistula (3-6 months before), AV graft or central venous
catheter (CVC)
• Extracorporeal circuit with heparin pump
• Blood from vascular access delivered to dialyser at 200-400 ml/min
– Entire blood volume through machine every 15 minutes
• Blood flows in opposite direction to dialysate – counter-current
– Maintains concentration gradient for maximum efficiency of diffusion
• Diffusion of solutes across semi-permeable membrane
• Ultrafiltration - to remove excess body water
– Achieved by altering hydrostatic pressure of dialysate compartment
• Patient is exposed to 120L of water each session
• For CRF: three times each week for about 4 hours
Peritoneal Dialysis
The semi permeable membrane: peritoneum
Dialysate infused into peritoneal cavity through a permanent
tunnelled Tenckhoff catheter
Peritoneal capillaries are the source of blood
The dialysate is exchanged either
• each night : automated peritoneal dialysis OR
• Regular exchanges during the day (Continuous ambulatory
peritoneal dialysis- CAPD)
• Usually 4 exchanges/day (20 minutes)
• 1.5-3 litres per exchange
–Solute normally contains sodium, chloride, lactate or bicarbonate.
–Ultrafiltration is controlled by altering the osmolality achieved with glucose or
other large molecular weight solutes in the dialysate.
• Convection of water and solutes across semi-permeable
• Blood via double lumen CVC passes through anticoagulation
port into dialyser at 100-200 ml/min
• Solutes move from blood to filtrate compartment driven by
positive hydrostatic pressure
• Allows extraction of larger molecular weight molecules than HD
• Similar filtration rate irrespective of solute size
• Large quantity of water removed requiring replacement fluid to
prevent hypovolaemia
• Replacement fluid – isotonic
• Haemofiltration rate of 1L/hr = 1L fluid removed and replaced
• Anticoagulation important due to activation of clotting cascades
• Combination of diffusion and convection
• Haemodialysis combined with haemofiltration
• Better removal of small and large molecules
(urea, B2 microglobulin,)
•Less problematic hypotension as losses
replaced by substitution fluid
Complications of Haemodialysis
Access related:
local infection,
creation of stenosis,
thrombosis or aneurysm.
During haemodialysis:
Hypotension (common),
cardiac arrhythmias,
air embolism
Nausea and vomiting,
Fever: infected central lines
Dialyser reactions: anaphylaxis
Heparin-induced thrombocytopenia
Disequilibration syndrome:
restlessness, headache,
tremors, fits and coma
Complications of Peritoneal Dialysis
– Complications
• Peritonitis (infective), also sclerosing peritonitis
• Catheter problems:
Blockage, kinking
Slow drainage
• Dietary complications
Hyperglycemia, poor diabetic control
weight gain (due to dextrose- avoid fats)
Malnutrition (need high protein diet)
• Others
Fluid retention/ hypovolaemia
Intraperitoneal bleeding
Hernias (incisional, inguinal, umbilical)
Back pain
– Amyloid
CRRT Therapy
(Continuous Renal Replacement Therapy)
• Slow Continuous Ultrafiltration (SCUF)
• Continuous Veno-Venous Haemofiltration (CVVH)
• Continuous Veno-Venous Haemodialysis (CVVHD)
• Continuous Veno-Venous Haemodiafiltration
• Continuous Ambulatory Peritoneal Dialysis
1. Acidosis with pH<7 not responding to treatment is an
indication for dialysis. TRUE
2. Gastritis, hypothermia, and fits are signs of uraemia.
3. CAPD involves one exchange of fluid a day. FALSE
4. Hypoglycaemia is a complication of peritoneal dialysis.
5. An abdominal wall stoma is not a contraindication to
peritoneal dialysis. TRUE
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