Free · Respiratory measurements

Rapid Shallow Breathing Measurement Index

Compute respiratory frequency divided by tidal volume in liters, retaining the historical 105 cutoff context.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Health results are educational estimates, not a diagnosis or treatment recommendation. A qualified clinician can interpret measurements in the context of your health.

Formula and method

20 breaths/min divided by 0.4 L gives RSBI 50 breaths/min/L.

RSBI = breaths per minute / tidal volume in liters = 1000 × rate / volume in mL.

Worked example

Enter these known values and leave the other values blank.

Respiratory rate
20 breaths/minute
Tidal volume
400 ml
RSBI
50

Assumptions and limitations

  • Measure respiratory frequency in breaths per minute and tidal volume in milliliters under a clinically appropriate consistent measurement method. The original 1991 adult study used f/VT as a weaning predictor. Ventilator support and measurement technique affect this value.
  • The output is read-only and preserves the source’s one-way relationship. It is an arithmetic index, not a ventilator-management recommendation. The 2024 AARC guideline suggests RSBI is not needed to determine spontaneous-breathing-trial readiness.

Common questions

Why does the formula multiply by 1000?

The input uses milliliters; dividing that value by 1000 converts it to liters.

Does RSBI below 105 mean extubation is safe?

No. The historical cutoff is a research predictor with imperfect accuracy, and the 2024 AARC guideline does not require RSBI to establish trial readiness.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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