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Continuous kidney replacement therapy (CKRT): overview

AKA: continuous renal replacement therapy (CRRT)

A general overview of the principles of continuous kidney replacement therapy in pediatric patients


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  • Uses an extracorporeal circuit similar to that used for
  • Runs continuously for the duration of the circuit life, which is usually several days
  • Particles can be removed by diffusion (same as
    ), convection, or a combination of the two
  • Fluid is removed by
    with hydrostatic pressure across the dialyzer membrane
  • The total clearance can be approximated by the total effluent rate (QE), the rate at which fluid is drained into the effluent bag
  • Continuous clearance, particularly convective clearance, results in significant solute loss over time
    • Electrolytes must be monitored closely and often replaced

CKRT typically performed in

  • Critically ill children
  • With oliguric AKI
  • That have failed medical management

Indications for CKRT rather than HD or PD

  • Hemodynamic instability (accurate, predictable
    over time)
  • Large volume needs (e.g., nutritional support, FFP, high volume meds)
  • Need for convective (vs. diffusive) clearance
    • Certain toxins/overdose agents may be more effectively removed via convective clearance


  • Diffusive clearance
    • Molecules move down a concentration gradient
  • Generally speaking, diffusive clearance works better for small molecules and convective clearance works better for middle molecules

Types of continuous kidney replacement therapy

SCUF: slow continuous ultrafiltration

Removal of fluid without replacing any fluid

CVVH: continuous veno-venous hemofiltration

  • Combined convective and diffusive clearance
  • Use of replacement fluids as well as countercurrent flow


Prime replaces the blood that is brought into

  • Normal saline
    • Default choice
  • 5% albumin
    • Somewhat hemodynamically unstable patients
    • Lots of aluminum in albumin products
  • Blood prime
    • Uses a single pass dialysis approach
      • Qb 30 mL/min
      • Qd 3600 mL/h (2x Qb)
      • All other rates off
      • Run for 5-6 minutes if using HF1000 or 2-3 minutes if using HF20 filter set
      • Give 1 mEq/kg NaHCO3 and 10 mg/kg CaCl to patient prior to start
  • Circuit to circuit change
    • Probably the least likely to cause hypotension
    • Used for unstable patients or if trying to avoid another blood prime
    • Suboptimal if line is sluggish
    • Not possible if the circuit has clotted or stopped
  • Returning the prime at the end of circuit life
    • If blood prime is used, do not return the blood to the patient
      • The blood in the circuit is the same