Renal Replacement Therapy

RRT Fundamentals - Kidney SOS Call

• RRT: Lifesaving support for kidney failure (acute/chronic), replacing filtration.
• Goals (Kidney SOS):
  • Solute clearance (uremic toxins, K⁺)
  • Overload (fluid) management
  • Stabilize acid-base/electrolytes
• Core Principles:
  • Diffusion: Solutes move via concentration gradient.
  • Convection: Solutes "dragged" with fluid.
  • Ultrafiltration: Fluid removal by pressure gradient.
• Indications (AEIOU 📌):
  • Acidosis (severe metabolic, pH < 7.1)
  • Electrolytes (refractory hyperK⁺ > 6.5 mEq/L)
  • Intoxications (e.g., SLIME - Salicylates, Lithium)
  • Overload (fluid, diuretic-resistant)
  • Uremia (symptomatic: pericarditis, encephalopathy)

⭐ Solute removal in hemodialysis is mainly diffusion; fluid removal (ultrafiltration) by hydrostatic pressure.

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RRT Indications - Dialysis Decision Time

Deciding when to initiate Renal Replacement Therapy (RRT) is crucial. The 📌 AEIOU mnemonic is a common guide:

• Acidosis: Severe metabolic acidosis (pH < 7.1-7.2) refractory to bicarbonate therapy.
• Electrolyte abnormalities:
  • Refractory hyperkalemia (K+ > 6.5 mEq/L with ECG changes or severe symptoms).
  • Symptomatic hypercalcemia, severe hypermagnesemia.
• Intoxications: Dialyzable toxins (e.g., Salicylates, Lithium, Ethylene glycol, Methanol, Barbiturates - 📌 SLIME-B).
• Overload (fluid): Pulmonary edema or severe volume overload refractory to diuretics.
• Uremia: Symptomatic uremia (e.g., pericarditis, encephalopathy, intractable nausea/vomiting, uremic bleeding).

⭐ Refractory hyperkalemia (K+ > 6.5 mEq/L with ECG changes despite medical therapy) is an absolute indication for urgent RRT.

RRT Modalities - The Dialysis Menu

-   SCUF (Slow Continuous Ultrafiltration): Fluid removal only.
-   CVVH (Continuous Veno-Venous Hemofiltration): Solutes by convection.
-   CVVHD (Continuous Veno-Venous Hemodialysis): Solutes by diffusion.
-   CVVHDF (Continuous Veno-Venous Hemodiafiltration): Convection + diffusion.

⭐ Continuous Renal Replacement Therapy (CRRT) is the preferred modality for hemodynamically unstable patients in the ICU due to its slower solute and fluid removal.

📌 Mnemonic for CRRT types (mechanism):

• SCUF: UF (UltraFiltration - fluid only)
• CVVH: Hemofiltration (convection - 'H'igh volume fluid)
• CVVHD: Dialysis (diffusion)
• CVVHDF: DiaFiltration (diffusion + filtration/convection)

RRT Complications & Anticoagulation - Clots & Calamities

• RRT Complications:
  • Hypotension (most frequent; volume shifts)
  • Dialysis Disequilibrium Syndrome (rapid urea ↓)
  • Bleeding (anticoagulation, uremia)
  • Infections (CRBSI, PD peritonitis)
  • Electrolyte imbalance (↓K⁺, ↓Ca²⁺, ↓PO₄³⁻, acid-base)
  • Technical: Filter clotting, air embolism, access.
• Anticoagulation: Prevents circuit clotting.
  • UFH: Standard; aPTT (1.5-2.5x baseline).
  • LMWH: Alternative; less monitoring; anti-Xa if needed.
  • RCA: Preferred in high bleeding risk.

    ⭐ Regional citrate anticoagulation is effective but requires monitoring for metabolic complications such as hypocalcemia (citrate chelates calcium) and metabolic alkalosis.

  • No Anticoagulation: High bleeding risk; saline flushes, high flow.
  • Argatroban/Danaparoid: For HIT.

High‑Yield Points - ⚡ Biggest Takeaways

• AEIOU criteria (Acidosis, Electrolytes, Intoxication, Overload, Uremia) mandate RRT initiation.
• CRRT is preferred for hemodynamically unstable patients; IHD for rapid correction.
• Regional citrate anticoagulation is choice for CRRT; prevents filter clots.
• Key RRT complications: hypotension (esp. IHD), circuit clotting, catheter-related infections.
• Preferred vascular access: Right Internal Jugular vein for acute RRT.
• SLEDD (Sustained Low-Efficiency Daily Dialysis) balances IHD and CRRT benefits.
• Always adjust drug doses for patients on RRT.