What is the standard continuous renal replacement therapy dose and how do I calculate the total effluent rate for a 70‑kg adult?

Standard CRRT Dose and Calculation for a 70-kg Adult

The standard CRRT dose is 20-25 mL/kg/hour of total effluent flow, which translates to 1,400-1,750 mL/hour (or 1.4-1.75 L/hour) for a 70-kg adult. 1

Evidence-Based Dosing Recommendations

The current standard is firmly established by Level 1A evidence from two landmark randomized controlled trials:

• The RENAL study (1,508 patients) compared CVVHDF at 40 mL/kg/h versus 25 mL/kg/h and found no survival benefit with higher intensity therapy 2, 1
• The ATN study (1,124 patients) compared intensive therapy (35 mL/kg/h) versus less intensive therapy (20 mL/kg/h) and similarly demonstrated no mortality benefit with higher doses 2, 1

These rigorous trials definitively established that doses above 25 mL/kg/h provide no additional survival benefit or improvement in kidney function recovery 2, 1. Earlier evidence suggesting benefit at 35 mL/kg/h compared to 20 mL/kg/h 2 has been superseded by these larger, more definitive studies.

Calculating Total Effluent Rate for a 70-kg Adult

Step 1: Determine Target Dose

• Target delivered dose: 20-25 mL/kg/hour 1
• For a 70-kg patient: 1,400-1,750 mL/hour 1

Step 2: Account for Prescribed vs. Delivered Dose Gap

Critical pitfall: The delivered dose typically falls significantly short of the prescribed dose, often achieving only 68% of what is prescribed 3. This occurs due to:

• Treatment interruptions (procedures, imaging, filter clotting) 4
• Natural decline in filter efficiency over time 4
• Average CRRT uptime of only 16 hours per day rather than continuous 24-hour therapy 3

Therefore, prescribe 25-30 mL/kg/hour to ensure delivery of 20-25 mL/kg/hour 4. For a 70-kg patient, this means:

• Prescribed rate: 1,750-2,100 mL/hour (1.75-2.1 L/hour) 4
• Expected delivered rate: 1,400-1,750 mL/hour 4

Step 3: Modality-Specific Calculations

The total effluent rate calculation differs by CRRT modality 1:

• CVVH (Continuous Venovenous Hemofiltration): Total effluent = ultrafiltration rate only 1
• CVVHD (Continuous Venovenous Hemodialysis): Total effluent = dialysate flow rate only 1
• CVVHDF (Continuous Venovenous Hemodiafiltration): Total effluent = dialysate flow rate + ultrafiltration rate 1

For example, if using CVVHDF on a 70-kg patient:

• Set dialysate flow at 1,500 mL/hour
• Set ultrafiltration at 500 mL/hour
• Total effluent = 2,000 mL/hour (28.6 mL/kg/h prescribed) 1

Monitoring and Quality Assurance

Frequent assessment of actual delivered dose is essential 2, 1. The gap between prescribed and delivered dose should be systematically monitored as a quality indicator 5, 4:

• Calculate hourly delivered dose: (total effluent volume in mL) ÷ (patient weight in kg) ÷ (hours of actual therapy) 4
• Adjust prescription iteratively to maintain target delivery 5
• Monitor for treatment interruptions and extend therapy time to compensate 4

Special Considerations

Body Weight Selection

• Use actual body weight for most patients when calculating dose 4
• Consider ideal body weight for severely underweight patients (BMI <16), as actual weight may underestimate effective volume of distribution 6
• For a 70-kg patient of average build, actual body weight is appropriate 6

Clinical Context

• Hemodynamically unstable patients particularly benefit from CRRT over intermittent hemodialysis 1
• Patients with acute brain injury or at risk for cerebral edema should receive CRRT preferentially 2
• Bicarbonate-based replacement fluids are preferred over lactate-based solutions 1

Avoiding Underdosing

A dose of 1,000 mL/hour is considered subtherapeutic for an 80-kg patient (equivalent to only 12.5 mL/kg/h) 7. For a 70-kg patient, anything below 1,400 mL/hour delivered dose risks inadequate solute clearance 7.