Maximum Ultrafiltration Rate in Hemodialysis
The maximum ultrafiltration rate in hemodialysis should not exceed 10 mL/kg/hour to minimize cardiovascular risk and mortality. 1
Physiological Basis for Ultrafiltration Rate Limits
Ultrafiltration (UF) is the process of fluid removal during hemodialysis, which primarily affects the extracellular fluid compartment. Two key physiological principles govern safe ultrafiltration:
- Plasma refill rate: The maximum rate at which extracellular fluid can replace contracting intravascular volume (approximately 5 mL/kg/hour) 2
- Intravascular volume contraction threshold: The rate at which coronary hypoperfusion, myocardial stunning, and vascular risk significantly increase (observed at ≥10 mL/kg/hour) 2
Evidence Supporting the 10 mL/kg/hour Limit
Research has demonstrated a clear relationship between ultrafiltration rates and patient outcomes:
- Ultrafiltration rates >13 mL/kg/hour are associated with a 59% increase in all-cause mortality and 71% increase in cardiovascular mortality compared to rates <10 mL/kg/hour 1
- The risk of mortality begins to increase at ultrafiltration rates exceeding 10 mL/kg/hour, regardless of heart failure status 1
- Even ultrafiltration rates between 10-13 mL/kg/hour show increased mortality risk in patients with congestive heart failure 1
Clinical Implications
When ultrafiltration rates exceed the plasma refill rate, several adverse consequences can occur:
- Intravascular hypovolemia
- Hemodynamic instability
- Myocardial stunning
- Organ hypoperfusion
- Accelerated loss of residual kidney function 3
Achieving Optimal Ultrafiltration
To maintain ultrafiltration rates below 10 mL/kg/hour while still achieving adequate fluid removal, clinicians have two main options:
Limit interdialytic weight gain through:
Extend dialysis session duration using the formula:
- Required treatment time (hours) = Volume to be removed (mL) / (10 × Weight (kg)) 2
Special Considerations
High-Volume Hemofiltration
For specific indications such as cytokine removal in critically ill patients, higher ultrafiltration volumes may be used:
- Continuous high-volume hemofiltration employs ultrafiltration volumes greater than 35 mL/hour/kg 4
- Super high flux hemofiltration can achieve ultrafiltration rates up to 6 L/hour in specialized settings for cytokine clearance 5
Intensive Dialysis Regimens
Alternative dialysis schedules can help maintain lower ultrafiltration rates while achieving adequate fluid removal:
- Short daily hemodialysis (2-3 hours, 6-7 sessions/week) 4
- Long nocturnal thrice-weekly regimen (8 hours/session) 4
- Long nocturnal daily regimen (8 hours, 6-7 nights/week) 4
Monitoring and Safety
To ensure safe ultrafiltration:
- Regularly assess pre- and post-dialysis weight
- Monitor blood pressure during treatment
- Evaluate for clinical signs of hypovolemia
- Consider bioimpedance spectroscopy where available 6
- Recognize that ultrafiltration primarily affects the extracellular fluid compartment 7
Pitfalls to Avoid
- Exceeding the 10 mL/kg/hour threshold - even modest increases above this rate are associated with increased mortality risk
- Ignoring patient-specific factors - patients with heart failure are more vulnerable to higher ultrafiltration rates
- Focusing solely on achieving target dry weight without considering the rate of fluid removal
- Overlooking the impact on residual kidney function - higher ultrafiltration rates are associated with faster decline in residual kidney function 3
In conclusion, while higher ultrafiltration rates may be necessary in specific clinical scenarios, maintaining rates below 10 mL/kg/hour should be the standard approach to minimize cardiovascular morbidity and mortality in chronic hemodialysis patients.