# Rapid shallow breathing index

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The rapid shallow breathing index (RSBI) is a tool that is used in the weaning of mechanical ventilation on intensive care units. The RSBI is defined as the ratio of respiratory frequency to tidal volume (f/VT). People on a ventilator who cannot tolerate independent breathing tend to breathe rapidly (high frequency) and shallowly (low tidal volume), and will therefore have a high RSBI.[1]

## Equation

${\displaystyle RSBI={\frac {f}{V_{T}}}}$

## Measurement

Measurement is done with a handheld spirometer attached to the endotracheal tube while a patient breathes room air for one minute without any ventilator assistance.[2]

## Example

As an example, a patient who has a respiratory rate of 25 breaths/min and an average tidal volume of 250 mL/breath has an RSBI of (25 breaths/min)/(0.25 L) = 100 breaths/min/L

## History

The concept was introduced in a 1991 paper by physicians from the University of Texas Health Science Center at Houston and Stritch School of Medicine at Loyola University in Chicago.[1]