Ultrafiltration Rate Limits for Intermittent Hemodialysis
The ultrafiltration rate should be limited to ≤13 mL/kg/hour to minimize intradialytic hypotension and cardiovascular complications, with rates exceeding 10 mL/kg/hour requiring careful monitoring and consideration of extended treatment time. 1, 2
Target Ultrafiltration Rate
Prescribe an ultrafiltration rate that balances achieving euvolemia and adequate blood pressure control while minimizing hemodynamic instability. 1
The optimal threshold is ≤10 mL/kg/hour based on physiologic principles, as this approximates the maximum plasma refill rate from extracellular fluid (~5 mL/kg/hour), preventing intravascular volume depletion faster than it can be replenished. 3
A practical upper limit of 13 mL/kg/hour has been validated in clinical practice, demonstrating reduced intradialytic hypotension without increasing volume overload hospitalizations. 2
Rates between 12-14 mL/kg/hour carry 2.5-fold increased odds of intradialytic hypotension, while rates >16 mL/kg/hour increase the risk 7.4-fold compared to rates <10 mL/kg/hour. 4
Calculating Required Treatment Time
When the required fluid removal exceeds safe hourly rates, extend the treatment duration rather than accepting higher ultrafiltration rates:
Treatment Time (hours) = Volume to Remove (mL) / [10 × Body Weight (kg)] 3
For patients with low residual kidney function (<2 mL/min), prescribe a minimum of 3 hours per session for thrice-weekly hemodialysis. 1
Consider additional sessions or longer treatment times for patients with large interdialytic weight gains, high ultrafiltration requirements, poorly controlled blood pressure, difficulty achieving dry weight, or poor metabolic control. 1
Strategies to Minimize Hypotension When Higher Rates Are Unavoidable
If ultrafiltration rates must exceed 10 mL/kg/hour due to clinical constraints:
Avoid excessive ultrafiltration by reassessing the estimated dry weight—hypotension may indicate the target weight is too low, particularly if accompanied by improving nutritional markers (rising albumin, creatinine, or normalized protein catabolic rate). 1
Perform isolated ultrafiltration first, then diffusive clearance sequentially, as ultrafiltration alone produces more favorable hemodynamic responses (increased stroke index, cardiac index, and mean arterial pressure), but extend total treatment time to compensate for reduced diffusive clearance time. 1
Increase dialysate sodium concentration to 148 mEq/L, especially early in treatment, with stepwise reduction later ("sodium ramping"), though this may increase interdialytic weight gain and blood pressure. 1
Reduce dialysate temperature to 34-35°C, which decreases symptomatic hypotension from 44% to 34% by increasing peripheral vasoconstriction and cardiac output through enhanced sympathetic tone. 1
Use bicarbonate-buffered dialysate rather than acetate, as acetate inappropriately decreases vascular resistance and increases venous pooling. 1
Automatic blood volume monitoring with feedback-controlled ultrafiltration adjustment reduces symptomatic hypotension by 13% and cramps by 32%, particularly benefiting patients with frequent intradialytic morbid events. 5
Special Populations
For hypoalbuminemic hospitalized patients (albumin <3 g/dL):
- Administer 100 mL of 25% albumin intravenously at dialysis initiation, which reduces hypotension events (from 15% to 7%) and allows higher ultrafiltration rates while maintaining hemodynamic stability. 6
Critical Pitfalls to Avoid
Do not rely on blood pressure alone to assess volume status—there is wide scatter between blood pressure and actual volume, and patients can have "silent overhydration" without clinical signs; use objective measures like bioimpedance spectroscopy. 7
Do not accept inadequate fluid removal due to hypotension concerns without first optimizing the ultrafiltration rate and treatment time—inadequate volume control increases cardiovascular morbidity and mortality. 7
Do not ignore residual kidney function—aggressive fluid removal may accelerate its decline, and dialysis dose can be reduced when residual clearance (Kru) is ≥2 mL/min if monitored periodically. 1
Recognize that achieving true dry weight takes time—the process may require 4-12 weeks, or up to 6-12 months in patients with diabetes or cardiomyopathy, and blood pressure may continue decreasing for 8+ months after volume normalization. 7