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CRRT (Continuous renal replacement therapy)

There are two forms of RRT.

  1. IRRT: intermittent renal replacement therapy
    • <24 hours
    • HD (hemodialysis)
    • SLEDD (sustained low efficiency daily dialysis)
      1. used for less stable patients; little slower than HD
  2. CRRT: continuous, >24h
    • Good for  those who are unstable/acute; slow and gentle.
    • Typical net fluid removal 0-200 cc/hour
    • Fluid (flow rates) 15-60 cc/min (into patient)
    • Fluid used: dialysate + replacement
    • Blood flow 150-200 cc/min

Clinical Indications

  • AKI
    • can be defined as:
      • SCr increase by >/= 0.3 mg/dL within 48 hours, OR
      • SCr increased to >/= 1.5 times baseline within 7 days, OR
      • Urine volume <0.5 cc/kg/hour in 6 hours
  • CRRT: hemodynaically unstable patients or patients with brain edema
  • Fluid overload


  • First choice: Right Internal Jugular (15cm, 14fr)
  • Second choice: femoral (24cm)
  • Third choice: Left Internal Jugular (20 cm)
  • Fourth choice: Subclavian

Always use a 20mL syringe to assess patency. Change lego (yellow) caps q7 daysCan be tunneled (with cuff) or non-tunneled

RRT Transport Mechanisms

  1. Ultra filtration: movement of fluid through a semi-permeable membrane driven by hydrostatic pressure
    • Removes water from fluid overloaded patients - no electrolyte balancing
  2. Adsorption: molecular adherance to the surface o the interior membrane (solute removal)
    • M60. M100. M150 - positively charged filters, attracts positively charged molecules to stick to it
    • HF series: neutrally charged filters (does not work through adsorption)
  3. Diffusion (hemodialysis): movement of solutes from high --> low concentration usin gdialysate solution
    • Uses dialysate to remove small molecules.
    • Prismasate - does not mix w/patients blood, pulls through semipermeable membranes 
  4. Convection/Hemofiltration: the forced movement of solutes with fluid (fluid will drag the solutes)
    • Removes large and medium (and small) molecules by increasing pressure gradient
    • Mixes w/patients blood: drug (Prismajol/Phoxillum)
    • Pre-filter replacement: deivers to circut access blood line before hemofiltere (to increase filter life)
      1. Blood will be diluted (decreased Hct)
      2. Decreased clearance
      3. The replacement "fluid volume" will be removed by the effluent pump

The Hemofilter

  • Filters waste products from the blood (mimics kidneys)
  • Dialysate goes in the green line and comes out the yellow line as effluent
    • Is used for diffusion/electrolyte balance
    • Once it comes out yellow line it is color of urine
  • Blood goes in the red access line, pulls from patient
  • Blood goes out the blue return line, returns to patient
  • replacement/substitute solution goes into the purple (for pre-replacement)  or white (for post-replacement) line 


"Paralyzes" calcium as soon as it is removed from the patient; once the citrate is metabolized by liver, can be utilized again. This prevents filter clotting

  • This calcium/citrate complex turns into bicarb
  • May add a calcium infusion post-filter to be returned back to patient
    • Essential for contractility in heart and blood vessels; used w/ a pump, start at 90 cc/hour
  • Concerns for using citrate:
    • Alkalosis (with trisodium citrate)
    • In acidosis: liver failure and lactic acidosis may decr body's ability to metabolize the Calcium/citrate complex, thus accumulating citrate = toxicity risk
    • Pressors may decrease the ability to metabolize the citrate/calcium complex

Citrate Toxicity

  • Calcium ratio = total Ca (mg/dL) * 0.25 / systemic iCa (mmol/L)
  • Detection: rising anion gap
    • Worsening metabolic acidosis
    • Falling systemic ionized calcium
    • Escalating Ca+ infusion requirements
      • Total Ca+: Systemi ion Ca ratio >2.1

Modes of therapy

  • Slow Continuous Ultrafiltration (SCUF)
    • goal is to remove patient fluid
  • Continuous veno-venous hemofiltration (CVVH)
    • goal for small, medium, and large molecule clearance. Involves patient fluid removal. No dialysate/diffusion
  • Continuous veno-venous hemodialysis (CVVHD)
    • goal to achieve small molecule clearance, remove patient fluid
  • Continuous veno-venous hemodiafiltration (CVVHDF)
    • goal for small, medium and large molecule clearance and patient fluid removal. Uses dialysate to pull solutes through diffusion.

CRRT Policy - Piedmont

  • Prior to starting CRRT:
    • Discontinue all electrolyte replacement protocols
    • D/c all diuretic orders
    • Draw an ionized calcium, BMP, mag, phos, PT/PTT, CBC
    • Have an ABG within last six hours
    • Unspoken roles: patients potassium + potassium we should give should be ~7
      • If potassium>5, consider using K of 2
      • If potassium<3, consider using K of 4
  • Fluid Balance
    • start fluid removal at 0 cc/hour for first 10-15 min
    • Titrate fluid removal every 15 min guided by blood pressure