Renal replacement therapy

Prescribing CRRT dose

Reviewed Nov 2026·3 references
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Write a CRRT prescription: modality, blood flow, effluent dose 20-25 mL/kg/h delivered, fluids, net ultrafiltration, and monitoring.

Definition
CRRT dose = effluent flow rate (replacement + dialysate + net UF) per kg per hour. KDIGO: deliver 20-25 mL/kg/h; prescribe ~25-30 mL/kg/h to allow for downtime. Higher doses (35-40) do not improve survival (RENAL, ATN).

At the bedside

  1. 1

    Modality and filter

    CVVHDF (or CVVH) with a high-flux filter (~1.0-1.5 m²).

  2. 2

    Blood flow

    Start 100-150 mL/min, increase to 150-250 mL/min as tolerated.

  3. 3

    Effluent dose

    Prescribe 25-30 mL/kg/h (actual body weight). Example split CVVHDF: replacement and dialysate equally; pre-dilution replacement (part) prolongs filter life but reduces efficiency.

  4. 4

    Fluids

    Bicarbonate-buffered solutions; adjust K (usually 4 mmol/L) and phosphate; avoid lactate buffer in liver failure/lactic acidosis.

  5. 5

    Net ultrafiltration

    Set hourly target (e.g. 0-150 mL/h) based on fluid goals and haemodynamics; review every 4-6 h.

  6. 6

    Keep filtration fraction < 20-25%

    FF = UF rate / plasma flow. High FF (convective, high UF, low blood flow, high haematocrit) clots filters. Use pre-dilution or increase blood flow.

  7. 7

    Monitor delivered dose

    Record downtime (filter changes, procedures, CT); adjust prescription if delivered < 20 mL/kg/h.

Worked CRRT prescription (70 kg, CVVHDF)

ParameterSetting
Target effluent dose25-30 mL/kg/h → 1,750-2,100 mL/h
Blood flow180 mL/min
Dialysate1,000 mL/h
Replacement (pre-filter 500 + post-filter 400)900 mL/h
Net UF100 mL/h
Total effluent2,000 mL/h ≈ 28.6 mL/kg/h
AnticoagulationRegional citrate (if no contraindication) or UFH

Example only; adjust to machine and unit protocol.

Red flag · call your senior now
Severe hypophosphataemia (< 1 mg/dL) and hypokalaemia are common after 24-48 h of CRRT: replace or use phosphate-containing solutions.
Pitfall
Prescribing exactly 20 mL/kg/h: downtime means delivered dose falls below target.
Pitfall
Ignoring the fluid balance of all other infusions (drugs, feeds) when setting net UF.
Pearl
Higher effluent doses also remove more antibiotics, amino acids and trace elements; there is no benefit beyond 25 mL/kg/h.

References

  1. 1

    Kidney Disease: Improving Global Outcomes (KDIGO) AKI Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl 2012;2:1-138 (summary: Nephron Clin Pract 2012;120:c179-84).

  2. 2

    RENAL Replacement Therapy Study Investigators. Intensity of continuous renal-replacement therapy in critically ill patients. N Engl J Med 2009;361:1627-38.

  3. 3

    VA/NIH Acute Renal Failure Trial Network. Intensity of renal support in critically ill patients with acute kidney injury. N Engl J Med 2008;359:7-20.

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Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.