RSBI Calculator

What Is the Rapid Shallow Breathing Index (RSBI)?

The Rapid Shallow Breathing Index (RSBI), also known as the Yang-Tobin Index, is one of the most widely used bedside clinical predictors for assessing whether a critically ill patient on mechanical ventilation is ready to be successfully weaned and extubated.

First described in 1991 by Drs. Karl Yang and Martin J. Tobin, RSBI evaluates the balance between respiratory rate and tidal volume. Patients who fail weaning trials typically develop rapid, shallow breathing patterns (high frequency, small tidal volume) to minimize respiratory muscle fatigue.

RSBI Formula and Calculation

RSBI is calculated as the ratio of respiratory frequency ($f$) to tidal volume ($V_T$) measured in liters:

$$\text{RSBI} = \frac{f}{V_T \text{ (in Liters)}} = \frac{\text{Respiratory Rate (breaths/min)}}{\text{Tidal Volume (mL)} / 1000}$$

Clinical Interpretation and Cutoffs

RSBI < 105 breaths/min/L: Favorable predictor. Indicates the patient is breathing efficiently without excessive tachypnea or severe hypoventilation. Associated with a high probability of successful spontaneous breathing trial (SBT) and extubation.
RSBI < 65 breaths/min/L: Highly favorable. Indicates exceptional pulmonary mechanics and strong respiratory drive.
RSBI > 105 breaths/min/L: Unfavorable predictor. Indicates rapid shallow breathing and a high risk (approximately 95%) of extubation failure. Mechanical ventilation should usually be continued while reversible factors are addressed.

How to Correctly Measure RSBI at the Bedside

Accurate measurement is critical for reliable RSBI values:

Discontinue ventilatory support for 1 minute (place the patient on a T-piece or minimal continuous positive airway pressure of 0–5 $\text{cmH}_2\text{O}$ with zero pressure support).
Measure the total expired volume and count the number of spontaneous breaths over exactly 60 seconds using a calibrated Wright spirometer or ventilator monitoring screen.
Divide the total minute volume by the number of breaths to calculate average tidal volume, or directly divide the respiratory rate by $V_T$ in liters.

Complementary Weaning Parameters

While RSBI is a cornerstone index, weaning decisions should also consider oxygenation metrics (such as the PaO2 FiO2 Ratio Calculator), hemodynamic stability, Glasgow Coma Scale, cough strength, and airway secretion burden.

Frequently Asked Questions

What is the normal RSBI threshold for extubation?

An RSBI below 105 breaths/min/L is the classic Yang-Tobin cutoff indicating a high likelihood of successful weaning from mechanical ventilation.

Can a patient fail extubation even with an RSBI < 105?

Yes. RSBI has high sensitivity (approx. 97%) but moderate specificity (approx. 64%). Upper airway edema, weak cough, copious secretions, or neurological depression can cause extubation failure despite normal respiratory mechanics.

Should pressure support be used while measuring RSBI?

Traditionally, RSBI must be measured with zero pressure support (CPAP only or T-piece). Adding pressure support artificially inflates tidal volume and lowers the RSBI score, creating false reassurance.

What is Minute Ventilation (VE) in relation to RSBI?

Minute ventilation is the total volume of air inhaled or exhaled per minute ($VE = f \times V_T$). Normal resting minute ventilation is between 5 and 8 L/min.

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