ICU Advantage Lecture: Principles of CRRT

Introduction

• Presenter: Eddie Watson
• ICU Advantage: Online critical care educational content.
• Subscription encouraged for more content.

Overview of CRRT

• CRRT: Continuous Renal Replacement Therapy
• Mimics nephron functions: fluid, electrolyte, waste, and acid-base balance.
• Understanding principles is key for using CRRT effectively.

Key Principles of CRRT

1. Diffusion

   • Movement of solutes from high to low concentration across a semi-permeable membrane.
   • Blood flows countercurrent to dialysate to maintain a concentration gradient.
   • Effective for small molecules.
   • Drives solute clearance in hemodialysis.

2. Ultrafiltration

   • Fluid movement across a membrane in response to pressure gradients.
   • Pressure types: osmotic, oncotic, hydrostatic.
   • Transmembrane pressure (TMP) determines ultrafiltration rate.
   • Key in removing fluid from the patient (hemofiltration).

3. Convection

   • Solute movement with water flow across a membrane.
   • Effective for small, medium, and large molecules.
   • Solute drag enhances clearance.
   • Requires fluid replacement to maintain patient balance.
   • Replacement solution delivery: pre-dilution (before filter) vs. post-dilution (after filter).

4. Adsorption

   • Solute adherence to the membrane's surface.
   • Causes filter clogging, reducing efficiency.
   • Filter material affects adsorptive properties.
   • E.g., Cytosorb filters for cytokine clearance.

Practical Considerations

• Dialysate composition affects solute clearance:
  • Sodium, Chloride, Magnesium: Match serum levels.
  • Potassium: Start with low levels, adjust as needed.
  • Bicarbonate: Added to dialysate for renal failure patients.
  • Waste Products: Urea and Creatinine cleared by diffusion.
• Fluid management strategies affect solute removal and patient balance.

Conclusion

• Four principles guide CRRT's mimicry of nephron functions.
• Understanding of principles is crucial for applying different modes of CRRT therapy.
• Future lessons will cover specific CRRT modes.

Additional Information

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