Why use it

Most validated single predictor of weaning success. Simple bedside measurement. High sensitivity (97%) at threshold < 105 for successful extubation. Part of standard SBT assessment protocols.

About

The Rapid Shallow Breathing Index (RSBI) is the ratio of respiratory frequency (f) to tidal volume (VT) measured during a spontaneous breathing trial (SBT). An RSBI < 105 breaths/min/L predicts successful extubation with high sensitivity. It is the most widely used and validated predictor of weaning outcome.

When to use

Before or during a spontaneous breathing trial (SBT)
Assessment of extubation readiness
Daily weaning screen in mechanically ventilated patients

Formula

RSBI = f / VT f = respiratory rate (breaths/min) VT = tidal volume (liters) Threshold: < 105 breaths/min/L = favorable

Pearls & pitfalls

Measure during spontaneous breathing (T-piece or low PSV 5-8 cmH₂O), NOT on full ventilator support.
RSBI should be measured within the first 1-3 minutes of the SBT.
RSBI < 105 has ~97% sensitivity but only ~65% specificity — some patients with RSBI < 105 still fail.
RSBI > 105 does NOT mean the patient cannot be extubated — it means higher failure risk.
VT must be in LITERS for the calculation (not mL).
Consider RSBI alongside other factors: mental status, cough strength, secretion burden, fluid balance.

Next steps

RSBI < 105: Favorable — proceed with SBT/extubation if other criteria met. RSBI > 105: Unfavorable — likely to fail weaning; investigate and treat underlying cause (secretions, weakness, fluid overload, anxiety). Repeat assessment after optimization.

Evidence

Derived by Yang and Tobin (N Engl J Med, 1991) in 100 medical ICU patients. RSBI < 105 had sensitivity 97%, specificity 64%, PPV 78%, NPV 95%. Extensively validated and universally adopted.

References

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):1445-1450. — link

RSBI (Rapid Shallow Breathing Index)

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