Renal replacement therapy

• Contention about when it should start, guidelines suggest when GFR is <15ml/min with symptoms
• Medical preparation involves Hep B vaccination and either creating an arteriovenous fistula for haemodialysis or inserting a Tenchkoff catheter for peritoneal dialysis
• Also give psychological support

Haemodialysis

• Blood flows on one side of a semi-permeable membrane while dialysis fluid flows in the opposite direction on the other side
• Solute transfer occurs by diffusion
• Ultrafiltration is the removal of excess lfuid by creating negative transmembrane pressure
• Problems;
  • Disequlibration syndrome – nausea, vomiting, headache, altered consciousness owing to rapid changes in plasma osmolality and cerebral oedema occurring on initial dialysis
  • Reduced BP and arrhythmias
  • Time consuming
  • Probs with access – thrombosis, stenosis, steal syndrome, ischaemia

Haemofiltration

• Blood is filtered continuously across a highly permeable synthetic membrane, allowing removal of waste products by a process of convection
• The ultrafiltrate is substituted with an equal volume of replacement fluid
• It is expensive and takes longer to do but there is less haemodynamic instability and so it is used for critically ill patients

Peritoneal dialysis

• PD fluid is introduced into the peritoneal cavity via a Tenchkoff catheter and uraemic solutes diffuse into it across the peritoneal membrane
• Ultrafiltration is achieved by adding osmotic agents e.g. glucose to the dialysis fluid
• Problems;
  • Peritonitis
  • Exit-site infection
  • Catheter malfunction
  • Los of membrane function
  • Obesity e.g. glucose in the dialysis fluid
  • Hernias
• Back pain

Complications of dialysis

• Cardiovascular disease
• Hypertension
• Anaemia
• Bleeding tendency due to platelet dysfunction
• Renal bone disease – treat with alfocalcidol, Ca2+ supplements and phosphate binders
• Infection
• ?2-microglobulin amyloidosis – causes carpal tunnel, arthralgia and fractures
• Acquired renal cysts
• Malignancy

Renal transplantation

Donors may be;

• Cadaveric – brainstem dead with supported ventilation and circulation
• Non-heart beating – without an active circulation
• Living related donor
• Living unrelated donor

Immunosuppressants

• Most regimes involve;
  • 1 – ciclosporin or tacrolimus
  • 2 – azothioprone or mycophenolate
  • 3 – prednisolone
• Pre-op anti-IL2 (basiliximab) reduces rates of early rejection

Complications

• Post-op
  • Bleed, thrombosis, infection, urinary leaks, oligouria
• Acute rejection
  • Occurs <6mth
  • Characterised by rising creatinine, fever and graft pain
  • Treat with high dose methylprednisolone, resistant cases require anti-thymocyte globulin
• Chronic rejection
  • >6mth
  • Gradual rise in creatinine and proteinuria
  • Not responsive to immunosuppression

Other complications

• Ciclosprorin or tacrolimus toxity – causes afferent arteriole vasoconstriction, causing reduced renal blood flow and ¯GFR
• Infection
• Malignancy
• Atheromatous vascular disease
• Hypertension