NephrologyTier 1Topic

End-stage renal failure - modes of dialysis, haemodialysis and peritoneal dialysis

Haemodialysis

In-centre: 4-5 h, 3x/week
Home HD: longer, more frequent (nocturnal 6-8 h x 5-6 nights) - best BP control, best phosphate control, best survival of the dialysis modalities
Access: AV fistula > AV graft >> tunnelled central venous catheter

No overall survival difference. PD tends to do better in the first 1-2 years, HD later; technique failure limits PD to ~5-8 years

~15,000 Australians on dialysis; ~80% HD, ~20% PD (ANZDATA)
Australia and New Zealand have among the highest home-therapy rates in the world (~25-30%)
PD technique failure ~10-15% per year
Peritonitis rate benchmark: <0.4 episodes per patient-year

HD - diffusion: blood and dialysate flow counter-current across a semipermeable membrane
- Ultrafiltration by a transmembrane hydrostatic pressure gradient
PD - the peritoneum is the membrane
- Dextrose (glucose) in the dialysate creates the osmotic gradient that drives ultrafiltration of water from blood into the dialysate
- Glucose is progressively absorbed -> the gradient dissipates -> ultrafiltration stops. This limits dwell length
- Icodextrin (glucose polymer, minimally absorbed) sustains ultrafiltration over the long dwell
- Higher dextrose concentration (1.5% / 2.5% / 4.25%) = more ultrafiltration + more glucose absorption

Transporter	Solute equilibration	Ultrafiltration	Prescription
High	Fast	Poor (glucose absorbed quickly)	Short frequent dwells - APD
Low	Slow	Good	Long dwells, large volumes - CAPD

Membrane transport becomes 'higher' over years of glucose exposure -> ultrafiltration failure

	Target
HD	spKt/V >=1.2 per session, URR >65%
PD	Weekly Kt/V >=1.7

Volume status, BP, phosphate and nutrition tell you more than Kt/V does
Residual renal function counts toward adequacy and independently predicts survival - protect it

Dry weight - the weight at which the patient is normotensive without oedema or intradialytic hypotension
Interdialytic weight gain - should be <4-4.5% of body weight (~2-2.5 kg)
Access examination: thrill, bruit, aneurysm, arm swelling (central stenosis), steal
PD: exit site, catheter function, effluent clarity, hernia, dwell tolerance

Intradialytic hypotension (~20-30% of sessions)
- Causes: excessive ultrafiltration rate, low dry weight, antihypertensives before dialysis, eating during dialysis, cardiac disease, sepsis
- Manage: stop ultrafiltration, Trendelenburg, saline bolus; then lengthen sessions, cool dialysate (35-36 C), reassess dry weight, hold antihypertensives pre-dialysis, midodrine
- Repeated intradialytic hypotension causes myocardial and cerebral stunning - it is not benign
Access problems
- Fistula: failure to mature, stenosis (rising venous pressure, prolonged bleeding after needling, dec thrill), thrombosis, steal syndrome, aneurysm, high-output cardiac failure
- Catheter: *bacteraemia (usually S. aureus or coagulase-negative staphylococci)*, dysfunction, central venous stenosis
  - Treat with systemic antibiotics + antibiotic lock; remove the line if S. aureus, fungal, tunnel infection, or persisting bacteraemia
Cramps, arrhythmia, sudden cardiac death - highest on the long interdialytic break
Disequilibrium syndrome - headache, nausea, confusion, seizures during the first sessions; prevented by short low-efficiency initial treatments
Anaphylactoid/first-use reactions; ACEi with AN69 membranes -> bradykinin accumulation
Dialysis-related amyloidosis (beta-2 microglobulin) - carpal tunnel, shoulder pain, bone cysts after years

PD peritonitis - the defining complication
- Diagnosis: 2 of 3 - abdominal pain / cloudy effluent / effluent WCC >100 x10^6/L with >50% neutrophils / positive culture
- Usually touch contamination; *coagulase-negative staphylococci and S. aureus commonest*
- Treat with intraperitoneal antibiotics - empirically covering Gram-positive (vancomycin or cephazolin) and Gram-negative (gentamicin or ceftazidime), then narrow on culture; 14-21 days
- *Remove the catheter for: fungal peritonitis, refractory peritonitis (no improvement at 5 days), relapsing peritonitis, faecal peritonitis, or tunnel infection*
- Polymicrobial with anaerobes or faecal organisms -> think a surgical intra-abdominal source
Inflow/outflow (drainage) failure
- *Constipation is the commonest cause - loaded bowel obstructs or malpositions the catheter. Exclude it first: AXR, then laxatives*
- Then: catheter migration, fibrin/clot (heparin in bags, urokinase), omental wrap, kinking
Ultrafiltration failure - high transporter status, glucose over-exposure, EPS; use icodextrin, shorten dwells
Mechanical - hernia, hydrothorax (pleuroperitoneal leak), genital oedema, back pain
Metabolic - glucose absorption -> weight gain, hyperglycaemia, hypertriglyceridaemia; protein loss in dialysate (~5-15 g/day)
Encapsulating peritoneal sclerosis - rare, late (>5 yrs), high mortality; bowel obstruction with a cocoon of fibrous tissue on CT

Fluid and dietary restriction (HD stricter); phosphate binders with meals
Anaemia: iron then ESA to Hb 100-115 g/L
CKD-MBD: phosphate control, calcimimetic/vitamin D analogue, PTH 2-9x ULN
Vaccination - hepatitis B double-dose x4, influenza, pneumococcal, COVID
Transplant assessment for everyone eligible - pre-emptive or early listing gives the best outcome
Withhold and re-dose drugs around dialysis as appropriate; avoid ACEi with AN69 membranes, avoid gadolinium and NSAIDs

Cardiovascular disease - LVH, heart failure, arrhythmia, sudden cardiac death: the leading cause of mortality
Infection - catheter bacteraemia (HD), peritonitis (PD): the second leading cause
Vascular calcification and calciphylaxis
Malnutrition-inflammation complex / protein-energy wasting
Dialysis-related (beta-2 microglobulin) amyloidosis
Acquired cystic kidney disease -> renal cell carcinoma
Depression, cognitive impairment, uraemic pruritus, restless legs, sexual dysfunction
Hepatitis B and C transmission risk (the reason for isolation policies and serological surveillance)
Encapsulating peritoneal sclerosis (PD), hernia, glucose-driven metabolic syndrome

Annual mortality ~15%; 5-yr survival ~40-50% - worse than most solid organ cancers
Median survival from start: age 20-24 ~20 yrs; age >75 ~2-3 yrs
PD technique survival ~5-8 years - most transfer to HD for peritonitis, ultrafiltration failure or mechanical problems
- Transfer to HD is an expected trajectory, not a failure of the decision
Residual renal function falls faster on HD than PD - preserving it improves survival on both
Transplantation approximately doubles life expectancy and improves quality of life

Monthly: UEC, Ca/PO4/PTH, FBE, iron studies, albumin, adequacy
Access surveillance; PD effluent and exit site at every visit
Annual: hepatitis serology, transplant reassessment, skin and cardiovascular review
Advance care planning - withdrawal accounts for 10-15% of deaths

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