Dialysis (Renal Replacement Therapy)

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Article Last Updated:27/03/2026

Definition

Dialysis refers to the artificial removal of 1) waste products, 2) excess fluid, and 3) electrolytes.

General Indications

AEIOU is a commonly used mnemonic to learn the indications for dialysis:

A – Acidosis (metabolic)	Severe, refractory metabolic acidosis (often <7.2)
E – Electrolyte (hyperkalaemia)	Severe, refractory hyperkalaemia
I – Intoxication	Key dialysable drug intoxications include aspirin, lithium, methanol, ethylene glycol
O – Oedema	Severe, refractory pulmonary oedema
U – Uraemia	Uraemia causing encephalopathy, pericarditis

Also consider dialysis if there are no symptoms + eGFR 5-7 mL/min/1.73m²

Dialysis Modalities

Acute Dialysis

Choice of acute dialysis:

If the patient is stable, intermittent haemodialysis is often used, typically via a non-tunnelled central venous catheter
If the patient is haemodynamically unstable, continuous renal replacement therapy is preferred

Clinical decisions in acute dialysis are primarily based on delivery modality (intermittent haemodialysis vs continuous renal replacement therapy), while the mechanism of solute clearance (haemodialysis vs haemofiltration) is typically determined by ICU protocols.

Chronic Dialysis

Haemodialysis (HD)

Mechanism	Blood is passed through an external filter (the dialyser), and solute is removed via diffusion
Access	1st line and gold standard: AV fistula However, this needs to be created 6 months before the anticipated start of dialysis to allow maturation Alternatives: Tunnelled catheter – typically used if immediate haemodialysis is necessary, as it does NOT need time for maturation AV graft – typically used if there is poor vessel access
Setting	Standard: in-centre (in hospital / satellite unit), or Home (if appropriate)
Frequency and duration	Standard in-centre HD schedule: 3x a week and 3-5 hours per session Home HD is typically more frequent and/or longer per session, but more flexible
Contraindications	Some relative contraindications: Severe haemodynamic instability (CRRT is preferred) Poor vascular access (PD is preferred if appropriate) Severe coagulopathy
Complications	Access-related: Infection (esp. with AV catheters) Thrombosis Stenosis Bleeding (esp. post-cannulation) Haemodynamic complications: Hypotension (common) Muscle cramps (from fluid and electrolyte shifts) Dialysis disequilibrium syndrome (rare) – rapid urea removal → osmotic shift → cerebral oedema

Peritoneal Dialysis (PD)

Mechanism	Dialysate is infused into the peritoneal cavity, and uses the peritoneum as a semi-permeable membrane Fluid is removed via osmosis (via glucose in the dialysate) Electrolytes, urea and creatinine are removed via diffusion
Access	A permanent peritoneal catheter is placed via the anterior abdominal wall
Setting	Home-based Patient-led, high independence (after training) With regular outpatient follow-up
Frequency and duration	Depends on the type: Continuous ambulatory PD 4–5 exchanges per day Each dwell lasts ~4–6 hours Performed during the day Patient can continue normal daily activities Automated PD Performed daily Typically overnight (6–10 hours) Uses a machine (cycler) Patient is asleep during dialysis
Contraindications	Loss of peritoneal membrane function Previous major abdominal surgery (s adhesions impair diffusion) Hernias IBDs Poor self-care ability
Complications	PD-associated peritonitis – most important Suspect if there is new abdominal pain + fever + cloudy dialysate Most commonly caused by Staphylococcus epidermidis Access-related Infection Catheter blockage Catheter malposition Mechanical Hernia (due to increased intra-abdominal pressure) Dialysate leak Abdominal discomfort (from fluid distension) Metabolic Hyperglycaemia and weight gain (as the dialysate contains glucose) Chronic Membrane failure Encapsulating peritoneal sclerosis (rare but serious)

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