Renal Replacement Therapy

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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). Ultrafiltration, Osmosis, Diffusion in Dialysis

⭐ 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 Fistula Types
    • 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:
    FeatureCAPD (Continuous Ambulatory)APD (Automated)
    MethodManual, 4-5 exchanges/dayMachine, overnight
    Advantage↑ Patient autonomy↑ Daytime freedom
  • Solutions: Glucose-based (osmotic agent); Icodextrin (long dwells, non-glucose).
  • Catheter: Tenckhoff (common type). Tenckhoff catheter placement
  • 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:
    TypePrinciple(s)Primary Removal
    SCUFUltrafiltrationWater
    CVVHConvectionMiddle molecules, water
    CVVHDDiffusionSmall molecules, water
    CVVHDFConvection + DiffusionBroad 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.

Schematic of CRRT circuit

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%.

Practice Questions: Renal Replacement Therapy

Test your understanding with these related questions

All of the following are indications for hemodialysis in acute kidney injury, EXCEPT:

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Flashcards: Renal Replacement Therapy

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_____ are the cornerstone of treatment for scleroderma renal crisis.

TAP TO REVEAL ANSWER

_____ are the cornerstone of treatment for scleroderma renal crisis.

ACE inhibitors

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