RSBI Calculator – Rapid Shallow Breathing Index

The rapid shallow breathing index, or RSBI, is a classic bedside weaning parameter used in mechanically ventilated patients. It compares how fast a patient is breathing with how much air they move in each breath. A person who breathes quickly but takes very small tidal volumes has a high RSBI, suggesting inefficient, shallow breathing that may not be sustainable after extubation. A lower index indicates a breathing pattern that is usually slower, deeper, and more efficient. Because the calculation only needs respiratory rate and tidal volume, it is simple to perform during a spontaneous breathing trial or other structured weaning assessment. The formula is respiratory rate divided by tidal volume expressed in liters. For example, a patient breathing 20 times per minute with a tidal volume of 500 mL has an RSBI of 40, which is often considered favorable. If another patient breathes 35 times per minute with a tidal volume of 250 mL, the RSBI is 140, which suggests significant shallow breathing and a higher chance of extubation failure. The widely taught threshold of 105 comes from validation studies showing that patients below that level were more likely to tolerate liberation from mechanical ventilation, although many clinicians prefer even lower values when the full clinical picture is uncertain. RSBI should never be interpreted in isolation. Weaning readiness also depends on oxygenation, mental status, secretion burden, cough strength, hemodynamic stability, respiratory muscle endurance, and the reason the patient needed ventilation in the first place. A good RSBI does not guarantee success if the patient is encephalopathic, profoundly weak, or unable to protect the airway. Likewise, a mildly elevated RSBI may still be acceptable in a patient who looks comfortable and has favorable gas exchange and strong cough mechanics. The number works best as one piece of a structured extubation decision rather than as a stand-alone rule. This calculator is intended for quick education and bedside support, especially when documenting or checking a spontaneous breathing trial. It can help students and clinicians verify the arithmetic instantly and see how the interpretation changes as respiratory rate or tidal volume shifts. Because patient safety decisions about extubation are high stakes, final interpretation should always be made by qualified clinicians who can integrate the full respiratory, neurologic, and hemodynamic picture.