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  • Continuous renal replacement therapy (CRRT) permits fluid and solute removal with greater hemodynamic stability than intermittent hemodialysis
  • Two principles underlie CRRT:
    • Diffusion: net movement of solute across semipermeable membrane from high concentrated compartment to low concentrated compartment. Dialysis is a diffusive process
    • Convection: movement of solute across semipermeable membrane due to transmembrane pressure gradient (also known as solvent drag). Hemofiltration is a convective process

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  • Fluid overload
  • Refractory hyperkalemia
  • Severe acidosis
  • Uremic symptoms
  • Heart failure

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  • More effective for fluid removal in hemodynamically unstable patient
  • Corrects abnormalities as they evolve, so better control of uremia, electrolyte, and acid–base balance
  • Facilitates administration of parental nutrition and obligatory intravenous medication as well as allowing continuous ultrafiltration
  • Less effect on intracranial pressure

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Four Main Types of CRRT
1Slow continuous ultrafiltration (SCUF)
  • No dialysate and replacement fluid required
  • Large fluid removal via ultrafiltration
2Continuous venovenous hemofiltration (CVVH)
  • Solute removed by convection
  • Dialysis solution is not used; instead a large volume of replacement fluid is infused either inflow or outflow of bloodline
3Continuous venovenous hemodialysis (CVVHD)
  • Solute removed by diffusion
  • Dialysis solution is passed through the dialysate compartment of filter in opposite direction of blood flow
4Continuous venovenous hemodiafiltration (CVVHDF)
  • Solute removed by diffusion and convection
  • Uses dialysate and replacement solution

NB: Arterial access is no longer used because of high complication rate.

(See Figure 208-1)

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Figure 208-1. Diagrams of the Four Main Types of Renal Replacement Therapy
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Technical Considerations
Access
  • Right internal jugular vein is preferred over any other central venous access as it is straight to superior vena cava
  • Femoral and subclavian accesses tend to kink and decrease flow
Replacement fluid
  • It is added either prefilter or postfilter of CVVH or CVVHDF circuit
  • Predilution (adding replacement fluid before filter) is better as it minimizes filter clotting and reduces downtime for CVVH machine
  • Either lactate- or bicarbonate-buffered CVVH or CVVHDF found equivalent degrees of correction of acidosis at 24 h, but lactate buffer cannot be used in lactic acidosis, hepatic failure, or liver transplant patient
  • Most commonly used fluids are Plasma-Lyte and 0.45% normal saline with 100 mEq/L of bicarbonate
Anticoagulation
  • Filter clotting is most frequent cause of therapy interruption in CRRT
  • There is no universally accepted anticoagulation
  • Unfractionated heparin is the most common agent for anticoagulation as it is easy to manage, easy to reverse, and inexpensive. Avoid if HIT
  • LMWH; not superior to unfractionated heparin
  • Citrate; avoid in hepatic failure, can cause hypocalcemia and, metabolic alkalosis
  • Prostacyclin; can cause systemic hypotension
  • No anticoagulation, for example, in liver transplant patient with high INR
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Complications of CRRT
Access
  • Thrombosis
  • Infection
  • Bleeding
Circuit-related complication
  • Air embolism
  • Disconnection/hemorrhage
  • ...

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