# 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.

Clinical Pearl

Subsequent meta-analyses consistently confirm the absence of survival benefit from early dialysis initiation. Evidence supports **symptom-driven initiation** rather than arbitrary eGFR thresholds.

### 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

| Solution | Glucose | UF Capacity | Use |
|----|----|----|----|
| Low | 1.5% | Minimal | Solute clearance when UF not needed |
| Intermediate | 2.5% | Moderate | Routine fluid management |
| High | 4.25% | Maximal | Significant fluid retention; limit frequent use |
| **Icodextrin** | Corn starch polymer | Sustained | Long dwells; patients with rapid glucose absorption |

### Peritoneal Equilibration Testing (PET)

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

| Transport | D/P Cr Ratio | Characteristics | Best Modality |
|----|----|----|----|
| High | \>0.81 | Rapid equilibration; good clearance but rapid glucose absorption, poor UF with long dwells | APD with short, frequent cycles |
| Low | \<0.50 | Slow equilibration; maintains UF throughout long dwells | CAPD with longer exchanges |

### 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

Critical Safety Warning

Post-dialysis K+ measurements taken within 15–30 minutes of treatment completion may **underestimate true values by 0.5–1.0 mEq/L**. Administering potassium supplements based on immediately post-dialysis levels can cause **life-threatening hyperkalemia**.

### 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

Clinical Pearl

Implement standardized protocols that **discourage routine post-dialysis K+ measurement** and emphasize pre-dialysis values. Track post-dialysis K+ supplementation rates as a quality metric — high rates indicate suboptimal practice patterns.

## Vascular Access

| Access Type | Maturation | Advantages | Disadvantages |
|----|----|----|----|
| **AV Fistula** | 6–12 weeks | Superior longevity; lowest complication rates; highest flow rates | Long maturation; not all patients have suitable anatomy |
| **AV Graft** | 2–4 weeks | Shorter maturation; when native fistula not possible | Higher infection and thrombosis rates; reduced lifespan |
| **CVC** | Immediate | Immediate access | Infection, thrombosis, central venous stenosis; minimize use |

## 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](https://pubmed.ncbi.nlm.nih.gov/20581422/)
2.  Rosansky S, et al. Early start of dialysis: a critical review. *Clin J Am Soc Nephrol*. 2011;6(5):1222–1228. [PubMed](https://pubmed.ncbi.nlm.nih.gov/21555505/)
3.  Li PK, et al. ISPD peritonitis guideline 2022 update. *Perit Dial Int*. 2022;42(2):110–153. [PubMed](https://pubmed.ncbi.nlm.nih.gov/35264029/)
4.  Hecking M, et al. Predialysis serum sodium and mortality (DOPPS). *Am J Kidney Dis*. 2012;59(2):238–248. [PubMed](https://pubmed.ncbi.nlm.nih.gov/21944663/)

## Related Mastery Modules


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