What is a normal RSBI?

Under 105 breaths/min/L is the conventional threshold associated with weaning success. Values well under 60 are reassuring; values above 105 suggest the patient is likely to fail a spontaneous breathing trial.

How do you calculate RSBI?

Divide the respiratory rate in breaths per minute by the tidal volume in litres. A patient breathing 24 times a minute with a 300 mL tidal volume has an RSBI of 24 ÷ 0.3 = 80.

Should RSBI be measured on pressure support?

It was described on minimal or no support. Pressure support increases the tidal volume the patient appears to generate, which lowers the index and can make a patient look more ready than they are.

Does a low RSBI mean the patient can be extubated?

No. It suggests the breathing pattern is not the limiting factor. Extubation also depends on airway protection, secretion clearance, mental status and whether the original reason for intubation has resolved.

Clinical Tool

RSBI Calculator

Rapid Shallow Breathing Index · Extubation readiness

Resp Rate (breaths/min)

Tidal Volume (mL)

RSBI

45.0

breaths/min/L

Excellent candidate

Strong predictor of successful extubation

Formula (Yang & Tobin, 1991)

RSBI = RR ÷ VT(L)

Where VT is in Liters, not mL

RSBI	Interpretation
<80	Excellent extubation candidate
<105	Acceptable — consider full picture
≥105	High risk of extubation failure

▸RSBI <105 was the original threshold (Yang & Tobin). Most institutions use <105 as the upper cutoff.

▸Measure during spontaneous breathing trial (SBT) on minimal or no support (CPAP 5 / PS 5 or T-piece).

▸RSBI alone has ~78% sensitivity, 74% specificity. Always combine with clinical assessment.

About the RSBI calculator

The rapid shallow breathing index is respiratory rate divided by tidal volume in litres. It puts a single number on the breathing pattern that tends to appear when a patient is not ready to come off the ventilator: fast and small rather than slow and deep.

How to measure it properly

RSBI is measured during a spontaneous breathing trial on minimal support — classically on a T-piece or on CPAP with little or no pressure support. Measuring it while the patient is still receiving substantial pressure support flatters the number, because the ventilator is supplying the tidal volume the patient is being credited with.

Yang and Tobin described the index in 1991 using a one-minute measurement taken after the patient had been disconnected from the ventilator. A value taken on 15 cmH₂O of pressure support is not the same measurement and should not be read against the same threshold.

What the threshold means

A value under 105 breaths/min/L was associated with successful weaning in the original cohort, and above it with failure. It is a threshold from one study population, not a physical constant, and it was intended to inform a decision rather than make it.

The index is better at predicting failure than success. A high RSBI is a reasonable reason to pause; a low RSBI does not by itself mean a patient will tolerate extubation, because it says nothing about airway protection, secretion burden, level of consciousness or the reason they were intubated in the first place.

Where it misleads

RSBI is affected by anything that changes rate or tidal volume for non-respiratory reasons — pain, anxiety, fever and metabolic acidosis all raise the rate. It also behaves differently in small patients and in women, in whom a smaller tidal volume is normal and pushes the index up without indicating weakness.

It is a weaning parameter, not a diagnosis. It belongs alongside the gas exchange, the mechanics and the clinical picture, not in place of them.

Common questions

What is a normal RSBI?: Under 105 breaths/min/L is the conventional threshold associated with weaning success. Values well under 60 are reassuring; values above 105 suggest the patient is likely to fail a spontaneous breathing trial.
How do you calculate RSBI?: Divide the respiratory rate in breaths per minute by the tidal volume in litres. A patient breathing 24 times a minute with a 300 mL tidal volume has an RSBI of 24 ÷ 0.3 = 80.
Should RSBI be measured on pressure support?: It was described on minimal or no support. Pressure support increases the tidal volume the patient appears to generate, which lowers the index and can make a patient look more ready than they are.
Does a low RSBI mean the patient can be extubated?: No. It suggests the breathing pattern is not the limiting factor. Extubation also depends on airway protection, secretion clearance, mental status and whether the original reason for intubation has resolved.

Educational reference for respiratory therapy students and clinicians preparing for the NBRC examinations. It supports clinical reasoning and does not replace institutional protocol, a device's instructions for use, or the judgement of the team caring for the patient.