What is the rapid shallow breathing index formula?

According to the American Association for Respiratory Care, the rapid shallow breathing index (RSBI) formula is an objective method by which a patient is considered ready to be weaned off of a ventilator. AARC notes that the RSBI formula was developed by Tobin and Yang.

The AARC states that the RSBI is calculated by dividing the patient's rate of respiration by their tidal volume. The rate was initially measured while patients were still intubated, but not receiving mechanical support with their breathing. AARC further explains that the outcome of an RSBI less than 105 is widely accepted as the point where patients should be weaned from ventilation.