Renal Replacement Therapy

RRT Fundamentals - Kidney SOS Signals

• Indications for RRT (Kidney SOS):
  • Absolute (Life-threatening):
    • Refractory hyperkalemia (>6.5 mEq/L + ECG changes)
    • Severe metabolic acidosis (pH <7.1)
    • Uremic emergencies (pericarditis, encephalopathy)
    • Refractory pulmonary edema
    • Certain intoxications (salicylates, lithium, methanol)
  • Relative:
    • Progressive azotemia (BUN >80-100 mg/dL)
    • Symptomatic uremia (nausea, fatigue)
    • Diuretic-resistant fluid overload

⭐ The AEIOU mnemonic (Acidosis, Electrolyte abnormalities, Intoxications, Overload (fluid), Uremia) is a key guide for initiating RRT in AKI.

• Core Principles:
  • Diffusion: Solute movement down concentration gradient (small molecules).
  • Convection: Solutes dragged with fluid flow (middle molecules).
  • Ultrafiltration: Fluid removal via pressure gradient.

RRT Modalities - Dialysis Dance Moves

• Intermittent Hemodialysis (IHD):
  • Rapid (3-4h) solute & fluid removal. High efficiency.
  • Mechanism: Primarily diffusion.
  • Pros: Widely available, quick K⁺/toxin removal.
  • Cons: Hemodynamic instability (hypotension), disequilibrium syndrome.
• Continuous Renal Replacement Therapy (CRRT):
  • Slow, continuous (24h) therapy; ideal for unstable patients.
  • Key Mechanisms & Variants:
    • CVVH (Continuous Veno-Venous Hemofiltration): Convection (middle molecules, sepsis).
    • CVVHD (Continuous Veno-Venous Hemodialysis): Diffusion (small solutes like urea).
    • CVVHDF (Continuous Veno-Venous Hemodiafiltration): Both (max clearance).

  ⭐ CRRT is generally preferred over IHD in hemodynamically unstable critically ill patients due to better hemodynamic tolerance.

• Sustained Low-Efficiency Daily Dialysis (SLEDD) / Prolonged Intermittent RRT (PIRRT):
  • Hybrid (6-12h sessions). Slower blood/dialysate flow rates than IHD.
  • Pros: Better hemodynamic tolerance than IHD; efficient solute clearance; flexible.
  • Cons: Less standardized; daily sessions.

Access & Anticoagulation - Pipes & Smooth Rides

• Vascular Access (Pipes)

  • Catheters: Non-cuffed (temporary, <3 wks), Cuffed (tunneled, >3 wks). Size: 11-14 Fr.
  • Sites (Ultrasound-guided):
    • Internal Jugular (RIJ preferred): ↓infection/thrombosis.
    • Femoral: ↑infection/thrombosis; emergency/contraindications to IJ/SCV.
    • Subclavian: ↑stenosis risk (avoid if future AVF).
  • Complications: CLABSI, thrombosis, stenosis, hematoma, pneumothorax.

• Anticoagulation (Smooth Rides)

  • Goal: Prevent filter clotting, maintain circuit patency.
  • Options:
    • None: High bleeding risk.
    • Systemic Heparin (UFH): Monitor aPTT (target 1.5-2x baseline or 45-60s).
    • Regional Citrate Anticoagulation (RCA): Preferred if ↑bleeding risk.

      ⭐ For regional citrate anticoagulation, meticulous monitoring of both systemic and post-filter ionized calcium is crucial to prevent toxicity and ensure efficacy.

      • Post-filter $iCa$ target: <0.4 mmol/L.
    • LMWH: Caution in renal failure (bioaccumulation).

RRT Management & Hurdles - Navigating the Flow

• Prescription & Dosing:
  • IHD: Target $Kt/V$ ≥ 1.2-1.4 per session for solute clearance.
  • CRRT: Effluent volume (dose) crucial for efficacy.

    ⭐ An effluent flow rate of 20‑25 mL/kg/hr is a common initial target for adequate solute clearance in CRRT.

• Monitoring & Adequacy:
  • Continuous: Hemodynamics (BP, HR), circuit pressures.
  • Regular: Fluid balance, electrolytes (K⁺, Ca²⁺, PO₄³⁻), acid-base status.
  • Assess adequacy: URR (IHD), delivered dose (CRRT).
• Complications & Troubleshooting:

-   ⚠️ Hypotension: Most common. Optimize fluid status, use vasopressors.
-   Filter Clotting: Key hurdle. Anticoagulation (citrate, heparin).
-   Infections: CRBSI risk. Strict aseptic technique vital.
-   Electrolyte shifts (K⁺, PO₄³⁻, Ca²⁺): Monitor, adjust dialysate/replacement fluids carefully.

High‑Yield Points - ⚡ Biggest Takeaways

• Indications for RRT: AEIOU (Acidosis, Electrolyte imbalance, Intoxication, fluid Overload, Uremia).
• CRRT (Continuous Renal Replacement Therapy) is preferred in hemodynamically unstable patients.
• Regional citrate anticoagulation is superior to heparin for reducing bleeding risk.
• Key complications: Hypotension, dialysis disequilibrium syndrome, catheter-related infections, and bleeding.
• Drug dosing requires careful adjustment in patients on RRT.
• Acute vascular access: Non-tunneled double-lumen catheter (e.g., femoral, jugular).
• SLED (Sustained Low-Efficiency Dialysis) offers a hybrid approach for select patients.