Write a short note on renal replacement therapy — haemodialysis, peritoneal dialysis and transplantation.

Definition and Modalities

Renal replacement therapy (RRT) substitutes for the excretory function of the failed kidney. Three modalities exist: haemodialysis, peritoneal dialysis and renal transplantation — the last being the only one that also restores endocrine and metabolic function.

Principles of Dialysis

Dialysis works by three physical processes across a semipermeable membrane:

• DIFFUSION — movement of solute down a concentration gradient (removes urea, creatinine, potassium); the dominant mechanism in haemodialysis
• ULTRAFILTRATION — movement of water down a pressure gradient (hydrostatic in haemodialysis, osmotic in peritoneal dialysis); removes fluid
• CONVECTION — solute dragged along with the water ("solvent drag"); removes middle molecules; the dominant mechanism in haemofiltration

Indications

Acute (AKI) — "AEIOU": Acidosis (refractory), Electrolytes (refractory hyperkalaemia), Intoxication (dialysable poisons — salicylates, lithium, methanol, ethylene glycol, metformin), Overload (pulmonary oedema unresponsive to diuretics), Uraemia (encephalopathy, pericarditis, bleeding).

Chronic (CKD stage 5): uraemic symptoms, refractory fluid overload or hyperkalaemia, malnutrition, and declining function — conventionally when GFR falls below about 10 mL/min (or 15 in diabetics), though the decision is increasingly symptom-led rather than number-led.

Haemodialysis

Blood is pumped through an extracorporeal dialyser ("artificial kidney") containing hollow fibres bathed in dialysate flowing counter-current to maximise the concentration gradient. Typically 3 sessions per week, 4 hours each.

Vascular access — the "Achilles heel" of haemodialysis:

Complications:

• During dialysis: HYPOTENSION (the commonest), cramps, nausea, headache, arrhythmia, disequilibrium syndrome (cerebral oedema from over-rapid urea removal in the first sessions — prevented by short, gentle initial treatments), and dialyser reactions.
• Access-related: infection, thrombosis, stenosis, aneurysm, steal syndrome with distal ischaemia, and high-output cardiac failure.
• Long-term: accelerated cardiovascular disease (the leading cause of death), anaemia, beta-2 microglobulin amyloidosis with carpal tunnel syndrome, bone disease, malnutrition, and transmission of hepatitis B and C where infection control is inadequate — a significant issue in some Indian dialysis units, making hepatitis B vaccination and strict segregation essential.

Peritoneal Dialysis (including Capd)

The peritoneum acts as the semipermeable membrane. Dialysate containing glucose (or icodextrin) as the osmotic agent is instilled into the peritoneal cavity through a permanent Tenckhoff catheter, left to dwell while solutes diffuse and water is drawn across by osmosis, and then drained.

Modalities: CAPD (continuous ambulatory peritoneal dialysis) — 3–5 manual exchanges daily, performed by the patient; and APD (automated peritoneal dialysis) — machine-driven exchanges overnight.

Complications of peritoneal dialysis:

• PERITONITIS — the major complication and commonest cause of technique failure. Presents with cloudy effluent (the earliest and most reliable sign), abdominal pain and fever. Diagnosed by effluent white cell count > 100/µL with > 50% neutrophils, plus culture. Treated with intraperitoneal antibiotics; catheter removal for refractory, relapsing or fungal peritonitis.
• Exit-site and tunnel infection; catheter malfunction and outflow failure.
• Metabolic: hyperglycaemia and weight gain from glucose absorption, dyslipidaemia, protein loss in the effluent.
• Mechanical: hernias, hydrothorax, back pain, abdominal distension.
• Encapsulating peritoneal sclerosis — rare but serious, after prolonged treatment.

Renal Transplantation

The treatment of choice for end-stage renal disease — it offers better survival, better quality of life and lower long-term cost than dialysis, and restores endocrine function (erythropoietin, vitamin D activation).

• Donor sources: living related and unrelated donors (which dominate in India, given the shortage of deceased donation) and deceased (brain-dead) donors. Pre-emptive transplantation before dialysis begins gives the best outcomes.
• Matching: ABO compatibility, HLA matching, and a negative crossmatch; desensitisation protocols allow ABO-incompatible transplantation in selected cases.
• Contraindications: active malignancy, active infection, severe irreversible comorbidity, active substance misuse, and inability to comply with immunosuppression.
• Immunosuppression: induction (basiliximab or anti-thymocyte globulin) followed by maintenance triple therapy — a calcineurin inhibitor (tacrolimus), an antiproliferative (mycophenolate) and corticosteroids.
• Complications:
• Rejection — hyperacute (preformed antibodies, immediate), acute (cellular or antibody-mediated, within months), and chronic.
• INFECTION — opportunistic organisms: CMV, BK virus, *Pneumocystis*, fungi, and TUBERCULOSIS (a major issue in India, requiring screening and often prophylaxis).
• Malignancy — skin cancers and post-transplant lymphoproliferative disorder (EBV-driven).
• Drug toxicity — calcineurin inhibitor nephrotoxicity, diabetes, hypertension, tremor, gum hypertrophy.
• Cardiovascular disease — the commonest cause of death with a functioning graft.
• Recurrence of the original disease in the graft (FSGS, IgA nephropathy, anti-GBM).
• In India, transplantation is governed by the Transplantation of Human Organs and Tissues Act, which regulates living donation, prohibits commercial dealing in organs, and requires authorisation committee approval for unrelated donors — an important medico-legal point.