About the RSBI Calculator - Rapid Shallow Breathing Index
The Rapid Shallow Breathing Index (RSBI), also called the f/VT ratio, is a bedside measurement used during mechanical ventilation weaning. It divides respiratory rate (breaths per minute) by tidal volume (in liters) during a period of spontaneous, unassisted or minimally supported breathing. First described by Yang and Tobin in 1991, it remains one of the most widely used single-number predictors of extubation readiness because it needs no special equipment beyond a ventilator display or spirometer.
How the RSBI is calculated
The formula is RSBI = f / VT, where f is the respiratory rate in breaths per minute and VT is the tidal volume in liters, both measured over the same short window of spontaneous breathing (commonly a T-piece trial or minimal pressure support). Because ventilators typically display tidal volume in milliliters, this calculator divides your entry by 1000 before dividing it into the respiratory rate, so the result stays consistent with the published 105 threshold. For example, a respiratory rate of 28 breaths per minute with a tidal volume of 350 mL (0.35 L) gives an RSBI of 28 / 0.35 = 80 breaths per minute per liter.
Reading the result
An RSBI at or below 105 breaths per minute per liter is associated with a higher likelihood of tolerating extubation, while a value above 105 is associated with a higher likelihood of weaning failure. A low RSBI generally reflects slower, deeper breathing; a high RSBI reflects fast, shallow breathing, which increases dead-space ventilation and signals that the respiratory muscles may be struggling with the current level of support. This calculator also reports tidal volume per kilogram of predicted body weight (using the standard height-and-sex formula), a secondary figure clinicians sometimes reference alongside RSBI to judge whether the tidal volume itself looks proportionate.
When to consult a professional
RSBI is one input among several used in a weaning assessment — it does not replace clinical judgment, oxygenation, hemodynamic stability, secretion burden, or mental status. Any decision about extubation or ventilator management should be made by the treating clinical team based on the full picture, not on this number alone.