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RSBI calculator (rapid shallow breathing index)

Study aid only. Not for clinical decisions. This calculator teaches textbook formulas for exam prep. It is not a medical device and does not replace clinical judgment, your facility's protocols, or a licensed clinician's assessment. Nothing you enter leaves your browser.

Formula

RSBI = f ÷ VT (in liters). In Yang and Tobin's study, an RSBI below 105 breaths/min/L predicted a successful weaning trial, and 105 or higher predicted failure.[1] Measure it while the patient breathes spontaneously, with minimal or no support.

Worked example

f = 30/min and VT = 300 mL (0.3 L): RSBI = 30 ÷ 0.3 = 100, which is below 105. Divide by liters, not milliliters. 30 ÷ 300 = 0.1 is the classic exam trap.

The RSBI is one piece of weaning readiness, together with the patient's underlying cause, oxygenation, hemodynamics, mental status, and secretions.[2]

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Sources

  1. Yang KL, Tobin MJ. Indexes predicting the outcome of weaning trials. NEJM 1991
  2. StatPearls: Ventilator Management

Formulas checked against the sources listed above on October 30, 2026. Written and reviewed by a practicing RRT for TidalPrep.