Rapid Shallow Breathing Index (RSBI) Calculator

How it is calculated

Enter the respiratory rate in breaths per minute and the tidal volume in millilitres, both measured during a spontaneous breathing trial. The tool converts the volume to litres and divides:

RSBI = respiratory rate ÷ (tidal volume in mL ÷ 1000)

The unit is breaths per minute per litre. The result is shown with two decimals, followed by a label that applies a single cut-off at 105: a value below 105 is labelled "weaning likely", and 105 or more is labelled "weaning unlikely". Exactly 105.00 falls on the unlikely side. The respiratory rate must be between 4 and 80 breaths per minute and the tidal volume between 100 and 2,000 mL; a volume between 0.1 and 2 is read as litres, and anything else gives no result. The label is a screening aid only; it does not replace clinical assessment, and it ignores oxygenation, cough, mental status and other factors.

Common mistakes

• Entering a per-kilogram figure (such as 6 mL/kg) instead of the volume of one breath. The field takes millilitres per breath, such as 320; a value from 0.1 to 2 is read as litres, and anything else outside 100 to 2,000 mL gives no result rather than a misleading RSBI.
• Using the ventilator's set rate or volume instead of the patient's own. The index is meant for a breathing trial with minimal support, so readings taken under full assist do not mean the same thing.
• Using the total minute volume rather than the average tidal volume per breath. RSBI divides by the volume of a single breath.
• Treating 104.99 and 105.00 as meaningfully different. The cut-off is a rule of thumb; values close to it deserve clinical judgment rather than a yes or no.
• Reading the label as a decision to extubate. It is one data point and takes no account of oxygen needs, secretions or the patient's mental state.