(RSBI) Respiratory rate (frequency) divided by tidal
volume. The units are typically bpm/L. This calculation
was developed as a weaning parameter, but its predictive
reliability has not been proven.
The RSBI is measured by attaching a hand-held spirometer
to the endotracheal tube and recording the respiratory
rate and average tidal volume over one minute,
though some ventilators will calculate this value for
For more information,
see 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.