How this calculator works
Rapid shallow breathing produces a higher respiratory-rate-to-volume ratio. The original Yang and Tobin study evaluated this index in patients undergoing a defined ventilator-weaning assessment. Measurement conditions affect performance, and an RSBI alone cannot establish readiness for extubation. This page returns the index without turning a historical cutoff into a treatment instruction. The result is an estimate for information only and is not medical advice.
Formula
RSBI = respiratory rate (breaths/min) / tidal volume (L). For an mL measurement, divide tidal volume by 1000 first.
Worked example
A respiratory rate of 20/min and tidal volume of 400 mL give 20/0.4 = 50 breaths/min/L. At 30/min and 250 mL, RSBI = 120 breaths/min/L.
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Frequently asked questions
Why does the formula use litres?
The index convention is breaths/min per litre. Using 400 instead of 0.4 for a 400 mL breath makes the result 1000 times too small.
Does a lower value guarantee successful extubation?
No. Airway protection, secretions, strength, gas exchange and the whole clinical assessment remain essential.
Can measurements on different support levels be compared directly?
Ventilator assistance and assessment technique can change respiratory rate and tidal volume. Record and interpret the conditions with the clinical team.