RSBI Calculator

Q: What is a normal RSBI value?

A healthy adult who breathes about 15 times a minute with 0.5 L breaths has an RSBI near 30 . In the ICU, most patients who pass a breathing trial land somewhere between 30 and 80 . Any score under 105 is counted as favorable, but the lower the number, the stronger the breathing pattern looks.

Q: What causes a high RSBI score?

A high score means breathing is fast and shallow. Common causes include: Weak or tired breathing muscles Stiff lungs from pneumonia, ARDS, or fluid overload Pain, fever, anxiety, or agitation Too much secretion in the airway A belly that is swollen or full of fluid, pushing on the lungs Low hemoglobin or a hidden infection Find and treat the cause instead of just repeating the test.

Q: How do you lower a patient's RSBI?

You lower it by fixing why the patient breathes fast and shallow. Helpful steps: Treat pain, fever, and anxiety Remove extra fluid with diuretics if the patient is overloaded Clear secretions and treat infection Sit the patient up at 30 to 45 degrees Rest the muscles on full support for 24 hours after a failed trial Give good nutrition and correct low potassium, magnesium, or phosphate As breaths get deeper and slower, the score drops.

Q: Can a patient be extubated with an RSBI over 105?

Yes. A score above 105 is a warning, not a ban. Many patients with a high score still do fine, especially women, patients with small breathing tubes, and patients who were suctioned right before the test. If oxygen levels, blood pressure, cough, and mental status all look good, the team may still pull the tube. The number is one piece of the decision.

Q: How long should a spontaneous breathing trial last before measuring RSBI?

The classic method reads the rate and tidal volume after about one minute of unassisted breathing. Many units also recheck the score near the end of a full trial, which usually runs 30 to 120 minutes . A score that starts low but climbs during the trial is a sign the muscles are tiring out.

Q: Does pressure support change the RSBI score?

Yes, and it makes the score look better than it really is. Pressure support pushes more air in, so breaths get bigger and the rate slows. That lowers the number. For a true reading, measure on a T-piece or with minimal support (CPAP of 5 or less and no added pressure support). Always note what settings were used.

Q: Is RSBI the same as the f/Vt ratio?

Yes. RSBI and f/V t are two names for the same number. The f is frequency (breaths per minute) and V t is tidal volume in liters. Some charts also call it the rapid shallow breathing ratio or the Tobin index, after Dr. Martin Tobin.

Q: What other tests are used with RSBI before extubation?

The team checks a whole set of items: Oxygen: PaO2/FiO2 above 150 to 200 with PEEP of 5 to 8 or less Muscle strength: negative inspiratory force (NIF) more negative than -20 to -30 cmH2O Cough: strong enough to clear the airway Secretions: not thick or too frequent Cuff leak test: checks for airway swelling Mental status: awake and able to follow simple commands Stable heart rate and blood pressure with little or no pressor support

Q: Does RSBI work the same way for children?

No. Kids breathe faster and take much smaller breaths, so the adult 105 cut-off does not fit them. Pediatric teams use a weight-adjusted version, dividing the rate by tidal volume per kilogram, with cut-offs near 8 to 11. Even then, the index is less proven in children than in adults, so the bedside exam matters more.

Q: Is RSBI useful for patients with a tracheostomy?

It can be measured, but it is less reliable. A trach tube is shorter and wider than a breathing tube, so it adds less work and the score often reads lower. For long-term trach patients who are weaning slowly, daily trial time tolerated is usually a better guide than a single RSBI number.

Introduction

The Rapid Shallow Breathing Index (RSBI) Calculator shows whether a patient on a ventilator may be ready to breathe on their own. It uses two numbers taken during a spontaneous breathing trial (SBT): the respiratory rate (breaths per minute) and the tidal volume (the air in one breath).

The math is simple. RSBI = respiratory rate ÷ tidal volume in liters. Fast, small breaths give a high score. Slow, deep breaths give a low score. A score under 105 is a good sign that the patient can be taken off the ventilator. A score of 105 or higher warns of a higher chance of weaning failure.

Enter your two values above to see the RSBI score. The calculator also reports the minute ventilation, how far the score sits from the 105 cut-off, and the exact tidal volume or breathing rate needed to stay under it. You can enter values in mL, L, cc, in³, or fl oz, and the calculator converts them for you.

RSBI is one piece of the extubation puzzle. Always use it with the full clinical picture, not on its own.

How to use our RSBI Calculator

Enter two numbers from your patient's spontaneous breathing trial (the respiratory rate and the tidal volume). The calculator divides the rate by the tidal volume in liters and gives you the Rapid Shallow Breathing Index (RSBI) score, tells you if it falls below or above the 105 cut-off, and shows the math step by step.

Respiratory Rate (f): Type the number of breaths the patient takes on their own in one minute during the trial. Most values fall between 12 and 20 breaths per minute. You can switch the unit menu to breaths per second if that is how your value was recorded.

Tidal Volume (Vt): Type the amount of air in one breath. Most values fall between 400 and 600 mL. Use the unit menu to pick mL, cc, L, in³, or fl oz. If you change the unit, the number you already typed is converted for you.

Calculate RSBI: Click this button to see the score, the gauge, the charts, and the tidal volume table. Results also update live as you type.

Reset: Click this to clear both fields and start a new RSBI calculation.

What Is the Rapid Shallow Breathing Index (RSBI)?

The Rapid Shallow Breathing Index, or RSBI, is a simple number that helps doctors and respiratory therapists decide if a patient on a ventilator can breathe on their own. It compares how fast a person breathes to how deep each breath is. Fast, shallow breathing is a warning sign that the lungs and breathing muscles are tired. Slow, deep breathing is a good sign.

The RSBI Formula

RSBI = respiratory rate (f) ÷ tidal volume (V_t in liters)

Respiratory rate is the number of breaths in one minute. Tidal volume is the amount of air in one breath. Tidal volume is often written in milliliters (mL), so you must divide it by 1,000 to get liters. For example, 26 breaths per minute with 400 mL breaths gives 26 ÷ 0.4 = 65 breaths/min/L.

How the Numbers Are Measured

RSBI is measured during a spontaneous breathing trial (SBT). The ventilator support is lowered or turned off for a short time while the patient breathes on their own, usually for about one minute. The rate and tidal volume are read from the ventilator or a handheld spirometer. The test is done while the patient is awake, calm, and not being suctioned.

What the Score Means

RSBI under 105 is favorable. The patient will likely do well after the breathing tube comes out.
RSBI 105 or higher is unfavorable. There is a higher chance of weaning failure and needing the tube put back in.

The 105 cut-off comes from the classic study by Yang and Tobin. A score below 105 is about 97% sensitive for successful extubation, which means very few patients who pass this test end up failing because of their breathing pattern.

Things That Can Skew the Score

Some factors push RSBI higher without meaning the patient is truly weak:

Female sex (smaller lungs and smaller tidal volumes)
A small endotracheal tube, which adds breathing work
Suctioning the airway during or right before the test
Pain, anxiety, or fever, which speed up breathing

How Clinicians Use It

RSBI is one piece of the puzzle, not the whole answer. Before extubation, the care team also checks oxygen levels, blood pressure, mental status, cough strength, secretions, and the reason the patient needed the ventilator in the first place. A high RSBI alone should not stop extubation if everything else looks good, and a low RSBI alone should not force it. Always pair the number with a full bedside exam.

This tool is for education and quick reference. It does not replace medical judgment or bedside assessment.

Formulas used

Rapid Shallow Breathing Index (RSBI)

\text{RSBI} = \frac{f}{V_t}

Tidal volume unit conversion to liters

V_t\,[\text{L}] = \frac{V_t\,[\text{mL}]}{1000}

Respiratory rate conversion to breaths per minute

f\,[\text{breaths/min}] = f\,[\text{breaths/s}] \times 60

Minute ventilation

\dot{V}_E = f \times V_t

Minimum tidal volume to keep RSBI below threshold

V_{t,\min} = \frac{f}{105}

Maximum respiratory rate to keep RSBI below threshold

f_{\max} = 105 \times V_t

Distance from the 105 threshold (absolute and percent)

\Delta = \left| \text{RSBI} - 105 \right|, \qquad \Delta\% = \frac{\Delta}{105} \times 100

Threshold classification

\text{RSBI} < 105 \Rightarrow \text{Favorable}, \qquad \text{RSBI} \ge 105 \Rightarrow \text{Unfavorable}

Frequently asked questions

What is a normal RSBI value?

A healthy adult who breathes about 15 times a minute with 0.5 L breaths has an RSBI near 30. In the ICU, most patients who pass a breathing trial land somewhere between 30 and 80.

Any score under 105 is counted as favorable, but the lower the number, the stronger the breathing pattern looks.

What causes a high RSBI score?

A high score means breathing is fast and shallow. Common causes include:

Weak or tired breathing muscles
Stiff lungs from pneumonia, ARDS, or fluid overload
Pain, fever, anxiety, or agitation
Too much secretion in the airway
A belly that is swollen or full of fluid, pushing on the lungs
Low hemoglobin or a hidden infection

Find and treat the cause instead of just repeating the test.

How do you lower a patient's RSBI?

You lower it by fixing why the patient breathes fast and shallow. Helpful steps:

Treat pain, fever, and anxiety
Remove extra fluid with diuretics if the patient is overloaded
Clear secretions and treat infection
Sit the patient up at 30 to 45 degrees
Rest the muscles on full support for 24 hours after a failed trial
Give good nutrition and correct low potassium, magnesium, or phosphate

As breaths get deeper and slower, the score drops.

Can a patient be extubated with an RSBI over 105?

Yes. A score above 105 is a warning, not a ban. Many patients with a high score still do fine, especially women, patients with small breathing tubes, and patients who were suctioned right before the test.

If oxygen levels, blood pressure, cough, and mental status all look good, the team may still pull the tube. The number is one piece of the decision.

How long should a spontaneous breathing trial last before measuring RSBI?

The classic method reads the rate and tidal volume after about one minute of unassisted breathing. Many units also recheck the score near the end of a full trial, which usually runs 30 to 120 minutes.

A score that starts low but climbs during the trial is a sign the muscles are tiring out.

Does pressure support change the RSBI score?

Yes, and it makes the score look better than it really is. Pressure support pushes more air in, so breaths get bigger and the rate slows. That lowers the number.

For a true reading, measure on a T-piece or with minimal support (CPAP of 5 or less and no added pressure support). Always note what settings were used.

Is RSBI the same as the f/Vt ratio?

Yes. RSBI and f/V_t are two names for the same number. The f is frequency (breaths per minute) and V_t is tidal volume in liters.

Some charts also call it the rapid shallow breathing ratio or the Tobin index, after Dr. Martin Tobin.

What other tests are used with RSBI before extubation?

The team checks a whole set of items:

Oxygen: PaO2/FiO2 above 150 to 200 with PEEP of 5 to 8 or less
Muscle strength: negative inspiratory force (NIF) more negative than -20 to -30 cmH2O
Cough: strong enough to clear the airway
Secretions: not thick or too frequent
Cuff leak test: checks for airway swelling
Mental status: awake and able to follow simple commands
Stable heart rate and blood pressure with little or no pressor support

Does RSBI work the same way for children?

No. Kids breathe faster and take much smaller breaths, so the adult 105 cut-off does not fit them. Pediatric teams use a weight-adjusted version, dividing the rate by tidal volume per kilogram, with cut-offs near 8 to 11.

Even then, the index is less proven in children than in adults, so the bedside exam matters more.

Is RSBI useful for patients with a tracheostomy?

It can be measured, but it is less reliable. A trach tube is shorter and wider than a breathing tube, so it adds less work and the score often reads lower.

For long-term trach patients who are weaning slowly, daily trial time tolerated is usually a better guide than a single RSBI number.

What happens if a patient fails a spontaneous breathing trial?

The patient goes back on full ventilator support and rests, usually for about 24 hours. The team then looks for the cause: heart failure, infection, weak muscles, fluid overload, oversedation, or low electrolytes.

After the cause is treated, the trial is repeated, often once a day. Failing one trial does not mean the patient will never come off the ventilator.

What tidal volume is good during weaning?

During a breathing trial, most adults pull 5 to 8 mL per kilogram of ideal body weight on their own, which is roughly 300 to 500 mL for an average adult.

Breaths under about 250 to 300 mL with a fast rate push the RSBI up and suggest the muscles are not ready.

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