Kidney Replacement Therapy

Timing of KRT Initiation

The IDEAL Trial: Paradigm Shift

The IDEAL trial (2010) randomized 828 patients: early initiation (eGFR 10–14) vs. late initiation (eGFR 5–7 or uremic symptoms). Results: no significant difference in survival, cardiovascular events, or quality of life. The early group experienced longer exposure to dialysis-related complications without measurable benefit.

Lead Time Bias

Many observational studies reporting survival advantages with early initiation failed to account for lead time bias — earlier detection creates the appearance of improved survival due to extended observation periods, not genuine clinical improvement. RCTs eliminate this bias.

Clinical Indicators for Initiation

• Uremic symptoms: Decreased appetite, nausea, vomiting, altered mental status, sleep disturbances, reduced functional capacity
• Refractory fluid overload: When optimal medical therapy fails to maintain euvolemia
• Metabolic acidosis: Serum bicarbonate consistently <15 mEq/L despite medical management
• Severe electrolyte abnormalities
• Uremic complications: Pericarditis, neuropathy

Peritoneal Dialysis

Principles

Peritoneal membrane (~1–2 m² surface area) serves as natural dialyzing surface. Dialysate creates concentration and osmotic gradients for solute removal and ultrafiltration. Small solutes move via diffusion; larger molecules via convection.

Catheter and Access

• Tenckhoff catheter: Most common; multiple side holes with curled tip
• Placement: Surgical, laparoscopic, or percutaneous
• Break-in period: 2–4 weeks for tunnel maturation; gradual volume escalation

Dialysate Solutions

Peritoneal Equilibration Testing (PET)

D/P creatinine ratio at 4 hours classifies transport status:

PD Modalities

• CAPD: 4 manual exchanges daily (4–6 hr dwells, 2–3 L volumes). Freedom from machines; requires dexterity and visual acuity.
• APD: Cycler performs 3–6 cycles over 8–10 hours overnight. May add daytime exchange with icodextrin.
• Tidal PD: Maintains tidal volume (50–85%) in abdomen; may reduce inflow pain. Higher dialysate consumption.

Hemodialysis

Circuit Design

• Blood flow rates: 300–450 mL/min; curvilinear clearance relationship with diminishing returns at higher flows
• Dialysate flow: 500–800 mL/min, counter-current direction; proportioned from acid + bicarbonate concentrates + treated water
• Temperature: 36–37°C standard; cooler dialysate improves hemodynamic stability
• Access recirculation: >10–15% indicates access dysfunction requiring intervention

Post-Dialysis Potassium Rebound

Mechanism

Rapid dialytic K+ removal from the intravascular compartment outpaces equilibration with intracellular stores (95% of total body K+ is intracellular). Potassium rebound occurs over 30 minutes to 2 hours as intracellular K+ redistributes to extracellular space.

Evidence-Based Management

• Use pre-dialysis K+ as the primary guide for dialysate K+ prescription and supplementation decisions
• If post-dialysis measurement needed, obtain ≥30–60 minutes after treatment (ideally 2 hours)
• Adjust dialysate K+ concentration rather than supplementing post-treatment
• If supplementation necessary, use oral K+ during the interdialytic period, not IV immediately post-dialysis

Vascular Access

Dialysis Adequacy

Kt/V

• K = dialyzer clearance, T = treatment time, V = urea distribution volume
• Target: spKt/V >1.2 per session for thrice-weekly HD
• Equilibrated Kt/V: typically 10–15% lower than single-pool (accounts for urea rebound)
• URR alternative: target >65%

PD Adequacy

• Weekly Kt/V >1.7 (peritoneal + residual renal clearance)
• Creatinine clearance >50 L/week/1.73 m²
• Monthly monitoring of residual renal function

Key Determinants of Adequacy

• Treatment time: Most powerful determinant; linear relationship with solute clearance
• Blood flow rate: Access flow must exceed prescribed Qb by ≥300–400 mL/min
• Dialyzer selection: Larger surface area = increased clearance; high-flux for middle molecule removal
• Vascular access type: AVF > graft > catheter for achievable flow rates

Technique Survival

• PD: 15–20% annual technique failure (inadequacy, complications, preference changes)
• HD: ~90% annual technique survival, limited primarily by access complications

Key References

1. Cooper BA, et al. Early versus late initiation of dialysis (IDEAL). N Engl J Med. 2010;363(7):609–619. PubMed
2. Rosansky S, et al. Early start of dialysis: a critical review. Clin J Am Soc Nephrol. 2011;6(5):1222–1228. PubMed
3. Li PK, et al. ISPD peritonitis guideline 2022 update. Perit Dial Int. 2022;42(2):110–153. PubMed
4. Hecking M, et al. Predialysis serum sodium and mortality (DOPPS). Am J Kidney Dis. 2012;59(2):238–248. PubMed

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