Renal Replacement Therapy (RRT)

Note: Davidson's Principles and Practice of Medicine, 24th Edition is not available in the library database. The following is a comprehensive, Davidson-style summary drawn from Comprehensive Clinical Nephrology, 7th Edition and Brenner & Rector's The Kidney - the most authoritative nephrology references available, whose content closely mirrors Davidson's coverage of RRT.

Definition and Overview

1. Haemodialysis (HD)
2. Peritoneal dialysis (PD)
3. Kidney transplantation

When to Initiate Dialysis

• eGFR: Dialysis is conventionally initiated when eGFR falls below ~10 mL/min/1.73 m²; in some centres, the mean initiation eGFR is 7-10 mL/min
• Uremic symptoms: nausea, vomiting, encephalopathy, pericarditis, pruritus
• Complications not manageable medically: volume-dependent hypertension, refractory hyperkalaemia, acidosis
• Malnutrition secondary to uraemia or gastroparesis
• Early vs. late start: The IDEAL trial showed no mortality benefit from early start dialysis (higher eGFR) vs. late start. Guided by symptoms rather than a fixed GFR cutoff.

• Uraemic encephalopathy
• Uraemic pericarditis
• Pulmonary oedema refractory to diuretics
• Severe refractory hyperkalaemia (K⁺ >6.5 mEq/L)
• Severe metabolic acidosis (pH <7.1)

Pre-dialysis Preparation

• Patients should be under nephrologist care from CKD Stage G3b-G4 onwards
• Predialysis education by a multidisciplinary team (MDT: dietician, pharmacist, nurse, social worker) improves outcomes and allows planned dialysis start
• Vascular access (AV fistula) or PD catheter should be placed well in advance
• Transplant listing should be discussed; pre-emptive transplantation (before dialysis) gives the best outcomes

1. Haemodialysis (HD)

Principle

• Diffusion (concentration gradient - small solutes like urea, creatinine, potassium)
• Ultrafiltration (convection - water removal by pressure gradient)

Access

Schedule and Dose

• Standard: 3 sessions/week, 4 hours each in-centre
• Dose measured by Kt/V (K = dialyser clearance, t = time, V = volume of distribution of urea); target single-pool Kt/V ≥ 1.2 per session
• Home HD: allows more frequent sessions (5-7x/week, overnight); improves BP control, reduces dietary restrictions, improves quality of life; used in 2-8% of dialysis populations globally

Hemodiafiltration (HDF)

• Combines diffusion (HD) + convection (haemofiltration)
• Removes larger middle molecules (e.g. β₂-microglobulin)
• High convection volumes (>30 L/wk/m²) needed for outcome benefit
• Widely used in Europe; not available in the USA

Contraindications to HD (relative)

• Difficult/no vascular access
• Needle phobia
• Severe cardiac failure
• Coagulopathy

2. Peritoneal Dialysis (PD)

Principle

Types

Access

• Tenckhoff catheter inserted surgically or radiologically; 2 weeks before starting PD

Dose

• Target: Weekly Kt/V (urea) ≥ 1.7 (including residual renal function)
• Residual kidney function (RKF) contributes significantly in early PD

Advantages of PD

• Home-based therapy - independence
• No needles
• Better preservation of residual kidney function
• More haemodynamic stability (beneficial in cardiac failure)
• No anticoagulation needed
• Better in patients with difficult vascular access

Contraindications to PD

Complications

• Peritonitis: most common serious complication; usually Gram-positive organisms (S. epidermidis, S. aureus); presents with cloudy effluent, abdominal pain, fever. Diagnosed by >100 WBC/mm³ in dialysate (>50% neutrophils)
• Exit site/tunnel infection
• Catheter malfunction (omentum wrapping, constipation)
• Encapsulating peritoneal sclerosis (EPS): rare, late complication; thickening/calcification of peritoneum

Technique Failure

• Infection, mechanical problems, inadequate dialysis, social reasons
• Technique failure due to infection carries higher short-term cardiac mortality risk

3. HD vs PD: Choosing a Modality

• Survival: No consistent superiority of one over the other in non-randomised studies
• PD is associated with superior health-related quality of life in some studies
• Some countries (e.g. Hong Kong) use a PD-first policy, with good results

4. Kidney Transplantation

• The best form of RRT for eligible patients
• Provides superior survival, quality of life, and cost-effectiveness over dialysis
• Pre-emptive transplant (before dialysis) gives the best graft and patient survival
• Sources: Living donor (related or unrelated) or deceased donor
• Diabetic patients: combined kidney-pancreas transplant may correct neuropathy and retard retinopathy

Survival advantage (Brenner & Rector)

• Adjusted relative risk of death after transplant vs. dialysis at 30 months = 0.26 (95% CI 0.11-0.46)
• 5-year survival: ~96% post-transplant vs. ~83% PD vs. ~81% HD (paediatric data, USRDS)

5. Conservative Management (Non-Dialytic Care)

• For patients who decline dialysis or are unlikely to benefit (elderly, high comorbidity)
• Focuses on: symptom control, dietary management, treatment of complications (anaemia, acidosis, oedema), advanced care planning
• Life expectancy on conservative management vs. dialysis in elderly, high-comorbidity patients may be comparable

Summary Table: RRT Modalities at a Glance