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Adaptive flow in dialysis how to set how to calculate benefits and contradiction

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hemodialysis AND dialysate flow

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adaptive flow hemodialysis set Qd Qb ratio contraindications

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https://freseniusmedicalcare.com/content/dam/fmcna/live/supp…

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Fresenius AutoFlow dialysate flow rate 1.5x 2x blood flow instructions for use

Adaptive flow / AutoFlow in hemodialysis usually means the machine automatically adjusts dialysate flow (Qd) according to the effective blood-flow rate (Qb). It is not an ultrafiltration setting.

How to set it

Only enable it when it is prescribed in the dialysis order and your unit's protocol permits it.

On Fresenius 2008 series

Select dialysate flow and scroll past 800 mL/min to choose:
  • AutoFlow 1.5×: target Qd is about 1.5 times Qb
  • AutoFlow 2×: target Qd is about 2 times Qb
The machine adjusts Qd as Qb changes, generally in 100 mL/min steps. The screen shows an “a” before the Qd value, for example a500. Confirm the actual displayed Qd after any change in blood flow. The 2008T operator manual specifies that AutoFlow is approximately linked to Qb and warns that the resulting Qd must still meet the required minimum.

Calculation

[ \textbf{Qd target} = \textbf{AutoFlow factor} \times \textbf{effective Qb} ]
Then the machine rounds/applies its allowed flow increment and range.
Effective QbAutoFlow 1.5×AutoFlow 2×
250 mL/min375 mL/min500 mL/min
300 mL/min450 mL/min600 mL/min
350 mL/min525 mL/min700 mL/min
400 mL/min600 mL/min800 mL/min
Example: if Qb falls from 400 to 300 mL/min because of access pressure or catheter limitation:
  • With 1.5× AutoFlow, Qd falls approximately from 600 to 450 mL/min
  • With 2× AutoFlow, Qd falls approximately from 800 to 600 mL/min
Use the value shown on that particular machine, not only the arithmetic result.

Which factor to use?

  • 1.5× is commonly used to reduce dialysate, water, concentrate, wastewater, and energy use while usually preserving most small-solute clearance.
  • 2× may be selected when higher diffusive clearance is required and water use is not the limiting concern.
  • A fixed Qd, often 500 to 600 mL/min, may be preferable where the prescription, adequacy plan, or local protocol requires it.
For modern dialyzers, increasing Qd above about 600 mL/min generally adds little urea, phosphate, or beta-2-microglobulin clearance, so the benefit of 800 mL/min may be modest. - Brenner and Rector's The Kidney, p. 2732

Benefits

  1. Maintains an appropriate Qd:Qb relationship
    If Qb drops, Qd reduces automatically rather than remaining unnecessarily high.
  2. Resource savings
    Lower dialysate use means lower water, concentrate, wastewater, and energy consumption. Fresenius describes AutoFlow as adapting Qd to effective Qb for this purpose in its AutoFlow overview.
  3. Minimal reduction in clearance in suitable patients
    Clearance rises with Qb and Qd only up to a plateau. Beyond that plateau, more Qd produces diminishing returns.
  4. Useful where Qb varies during treatment
    Examples include variable access flow, catheter dysfunction, alarms, or a prescribed lower Qb.

Contraindications / when to avoid or be cautious

There are no universal patient-specific absolute contraindications to AutoFlow itself. The important issue is whether the lower automatic Qd can still deliver the prescribed dialysis dose.
Do not use it, or reassess it, when:
  • The displayed AutoFlow Qd is below the prescribed or machine-specific minimum.
  • Delivered adequacy is low, such as low spKt/V, low stdKt/V, poor URR, persistent hyperkalemia, hyperphosphatemia, or inadequate uremic symptom control.
  • Qb is low because of a correctable access problem. Do not use AutoFlow to hide catheter dysfunction, access stenosis, recirculation, needle malposition, or excessive negative arterial pressure. Correct the cause and reassess access.
  • A high fixed Qd is specifically prescribed, for example as part of an individualized adequacy plan.
  • The patient has a large solute burden or requires intensified clearance, where reducing Qd could make adequacy harder to achieve within the available treatment time.
  • There is machine-specific incompatibility or an active alarm/technical issue. Follow the exact operator manual and local policy.
AutoFlow does not replace adequacy monitoring. Kt/V depends on actual clearance, treatment time, access recirculation, dialyzer, Qb, Qd, ultrafiltration, and patient total body water, not just the Qd:Qb ratio.

Practical safe workflow

  1. Verify prescription: treatment duration, target Kt/V, dialyzer, Qb, Qd/AutoFlow factor, and UF goal.
  2. Establish the best safe effective Qb.
  3. Select AutoFlow 1.5× or 2× only if ordered.
  4. Confirm the displayed Qd is not below the required minimum.
  5. Monitor arterial/venous pressures, access function, alarms, and effective Qb.
  6. Review delivered dose and clinical biochemical targets.
  7. If adequacy falls, first check access, recirculation, delivered treatment time, anticoagulation/dialyzer clotting, and Qb before simply increasing Qd.
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