Hemodialysis Ultrafiltration Rate Calculator
Total Fluid to Remove:
0 L
Hourly Removal Rate:
0 ml/hr
Normalized UFR:
0 ml/kg/hr
Understanding Ultrafiltration Rate (UFR) in Hemodialysis
The Ultrafiltration Rate (UFR) is a critical hemodynamic metric used in dialysis treatment. It represents the speed at which fluid is removed from a patient's blood during a hemodialysis session. Managing UFR is essential for patient safety, as removing fluid too quickly can lead to intradialytic hypotension, cramping, and "myocardial stunning" (strain on the heart).
Why Calculate UFR?
Nephrologists and dialysis technicians monitor UFR to ensure that fluid removal matches the patient's cardiovascular capacity to refill the vascular space. The Normalized UFR takes the patient's body size into account, providing a more accurate risk assessment than the raw hourly rate alone.
The UFR Formula
To calculate the Ultrafiltration Rate, you need the patient's pre-dialysis weight, their target (dry) weight, and the duration of the treatment session. The calculation involves three steps:
1. Total Fluid Volume (L):
Volume = Pre-Dialysis Weight (kg) – Target Weight (kg)
2. Hourly UFR (ml/hr):
Hourly Rate = (Volume × 1000) / Treatment Time (hrs)
3. Normalized UFR (ml/kg/hr):
Normalized Rate = Hourly Rate / Target Weight (kg)
Volume = Pre-Dialysis Weight (kg) – Target Weight (kg)
2. Hourly UFR (ml/hr):
Hourly Rate = (Volume × 1000) / Treatment Time (hrs)
3. Normalized UFR (ml/kg/hr):
Normalized Rate = Hourly Rate / Target Weight (kg)
Example Calculation
Consider a patient with a pre-dialysis weight of 84 kg and a prescribed dry weight of 81 kg. The treatment is scheduled for 4 hours.
- Fluid Removal: 84 kg – 81 kg = 3 kg (3 Liters or 3000 ml).
- Hourly Rate: 3000 ml / 4 hours = 750 ml/hr.
- Normalized UFR: 750 / 81 = 9.26 ml/kg/hr.
Safe Clinical Limits
Clinical studies and guidelines (such as those from KDOQI and CMS) suggest specific thresholds for Normalized UFR to reduce mortality risk:
- < 10 ml/kg/hr: Generally considered the safest zone for preserving residual kidney function and cardiovascular health.
- 10 – 13 ml/kg/hr: Cautionary zone. High fluid removal rates in this range may require longer treatment times or more frequent sessions.
- > 13 ml/kg/hr: High risk. Consistently exceeding this rate is associated with higher rates of all-cause mortality and cardiovascular hospitalization.
Tips for Managing UFR
If the calculated UFR is too high, clinical teams may consider:
- Extending the treatment time (e.g., from 3.5 to 4 hours).
- Reviewing dietary salt and fluid intake to reduce interdialytic weight gain.
- Adding an extra dialysis session during the week.