Renal Replacement Therapy

RRT Indications & Principles - Start Smart

• Acute Indications (📌 AEIOU):
  • Acidosis (metabolic, pH < 7.1)
  • Electrolytes (hyperkalemia K+ > 6.5 mEq/L, refractory)
  • Intoxications (e.g., salicylates, lithium)
  • Overload (fluid, diuretic-refractory)
  • Uremia (pericarditis, encephalopathy)
• Chronic Indications:
  • eGFR < 15 mL/min/1.73m² (CKD Stage 5)
  • Uremic symptoms (intractable)
• Core Principles:
  • Diffusion: Solutes via concentration gradient.
  • Ultrafiltration: Fluid via pressure gradient.
  • Convection: Solutes with fluid (solvent drag).

⭐ Refractory hyperkalemia (K+ > 6.5 mEq/L, ECG changes) is a key emergency RRT indication.

RRT: Hemodialysis - Blood Butler

• Vascular Access:
  • AV Fistula (AVF): Gold standard. Maturation 6-8 wks. Complications: Steal syndrome, thrombosis.
  • AV Graft (AVG): Use if AVF fails. Maturation 2-3 wks. Higher thrombosis/infection.
  • Central Venous Catheter (CVC): Temporary/urgent. High infection risk (⚠️).
• Dialyzer: Synthetic semipermeable membrane (e.g., polysulfone).
• Anticoagulation: Systemic heparin (UFH/LMWH), regional citrate, or heparin-free.
• Key Complications:
  • Hypotension (most common).
  • Muscle cramps.
  • Dialysis Disequilibrium Syndrome.
  • Access site infection/stenosis.

⭐ The Brescia-Cimino fistula, an anastomosis between the radial artery and cephalic vein at the wrist, is the preferred initial AVF.

RRT: Peritoneal Dialysis - Belly Wash

• Principle: Peritoneal membrane as natural, semipermeable dialyzer. "Belly Wash".
• Types:

  Feature	CAPD (Continuous Ambulatory)	APD (Automated)
  Method	Manual, 4-5 exchanges/day	Machine, overnight
  Advantage	↑ Patient autonomy	↑ Daytime freedom

• Solutions: Glucose-based (osmotic agent); Icodextrin (long dwells, non-glucose).
• Catheter: Tenckhoff (common type).
• Complications:
  • Peritonitis: Cloudy effluent, abdominal pain, fever. Dx: PD fluid WBC >100/µL (>50% PMNs). Rx: Intraperitoneal (IP) antibiotics.
  • Exit site/tunnel infections.
  • Hernias, hyperglycemia, catheter dysfunction.

⭐ Most common organisms in PD peritonitis: Coagulase-Negative Staphylococci (e.g., Staphylococcus epidermidis), followed by Staphylococcus aureus.

RRT: CRRT & SLED - ICU Saviors

CRRT for hemodynamically unstable ICU patients with severe AKI.

• CRRT Modalities:

  Type	Principle(s)	Primary Removal
  SCUF	Ultrafiltration	Water
  CVVH	Convection	Middle molecules, water
  CVVHD	Diffusion	Small molecules, water
  CVVHDF	Convection + Diffusion	Broad solutes (small/middle), water

• Anticoagulation: Regional Citrate (RCA) preferred.
• SLED (Sustained Low-Efficiency Dialysis): Hybrid approach.
  • Pros: ↑hemodynamic stability vs IHD, ↓duration vs CRRT.
  • Cons: Resource intensive.

⭐ CVVHDF offers the most comprehensive solute clearance and fluid balance control.

RRT: Complications & Special Topics - Trouble Tidbits

• Long-term:
  • β2-microglobulin amyloidosis (esp. joints, carpal tunnel)
  • Protein-energy wasting (malnutrition)
  • Accelerated cardiovascular disease (CVD)
• Dialysis Adequacy: Measured by $Kt/V$.
  • HD target: ≥1.2 per session (urea reduction ratio >65%)
  • PD target: Weekly total $Kt/V$ ≥1.7
• RRT in Poisoning:
  • For severe cases unresponsive to conservative measures.
  • 📌 I STUMBLE: Isopropanol, Salicylates, Theophylline, Uremia, Methanol, Barbiturates, Lithium, Ethylene glycol.
• RRT in Pregnancy: Generally safe; requires intensified regimens.

⭐ Beta-2 microglobulin amyloidosis, often presenting as carpal tunnel syndrome, is a significant complication of long-term hemodialysis.

High‑Yield Points - ⚡ Biggest Takeaways

• RRT Indications (AEIOU): Acidosis, Electrolyte imbalance (K↑), Intoxication, Fluid Overload, Uremia.
• HD uses diffusion; HF/CVVH uses convection for solute and fluid removal.
• PD major risk: peritonitis (Staph); also hyperglycemia.
• CRRT is preferred for hemodynamically unstable ICU patients.
• AV fistula: preferred HD access, matures 6-8 weeks.
• Dialysis disequilibrium syndrome: rapid urea ↓ causes neuro sx; slow initial HD.
• HD Adequacy: Kt/V urea ≥ 1.2 (3x/week); URR > 65%.