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Rapid shallow breathing index (Yang–Tobin)

Also called RSBI, f/VT, Tobin index, weaning index

Respiratory frequency divided by tidal volume (litres) to predict the outcome of a weaning trial.

/min

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Formula and scoring

RSBI = respiratory rate (/min) ÷ tidal volume (L). Threshold 105 breaths/min/L.

Exam and ward pearls

  • In Yang & Tobin (NEJM 1991) f/VT had sensitivity 0.97, specificity 0.64 and ROC area 0.89 – better at ruling in success than predicting failure.

When not to rely on it

  • Derived in 100 ventilated patients; values depend on measurement conditions and many later studies used lower thresholds. Use alongside a spontaneous breathing trial, not instead of one.

Source

  1. Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991;324(21):1445-50. doi:10.1056/NEJM199105233242101 · PMID 2023603
  2. Karthika M, Al Enezi F, Pillai LV, et al. Rate of change of rapid shallow breathing index and extubation outcome in mechanically ventilated patients. Crit Care Res Pract. 2023;2023:9141441 (states the Yang–Tobin 105 breaths/min/L threshold). doi:10.1155/2023/9141441 · PMID 37795474

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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