RSBI Calculator - Yang Tobin f/Vt Score

An RSBI calculator turns a respiratory rate and a tidal volume into the rapid shallow breathing index used to screen a ventilated patient for weaning readiness. The result is read against the 105 breaths per minute per liter cut-off that Yang and Tobin reported in 1991, and the same number helps the team decide whether a spontaneous breathing trial is likely to succeed before the endotracheal tube is removed.

• • Spontaneous breathing trial screening: run the f over Vt ratio after 30 to 120 minutes of unsupported breathing to see if the patient sits in the band that predicts successful extubation.
• • Respiratory therapy teaching: use the same ratio with a teaching set of numbers to show how a faster rate or a shallower breath moves the index past 105.
• • Tracheostomy collar trials: track the ratio across successive weaning trials to see whether the index trends down as the patient regains respiratory strength.
• • Pre-extubation safety check: pair the index with mental status, cough strength, and oxygenation before extubation.

The ratio is read as breaths per minute divided by tidal volume in liters, so a calm patient breathing deeply lands at the low end of the scale and a distressed patient breathing rapidly and shallowly lands above 105. The number does not replace a full weaning assessment, so the calculator sits next to the rest of the bedside picture.

When the same ventilated patient is also being scored for ICU severity, the Apache II Calculator returns the 0 to 71 Knaus score from the same admission data set.

The RSBI calculator reads the entered respiratory rate and tidal volume, converts the tidal volume from milliliters into liters, divides the rate by that liter value, and returns the index together with the 105 breaths per minute per liter cut-off. The same arithmetic is used in the original Yang and Tobin 1991 paper and in the bedside workflow that followed it.

• f (respiratory rate): Number of breaths per minute counted on the spontaneous breathing trial. Rates above 20 breaths per minute are usually called tachypnea.
• Vt (tidal volume): Tidal volume in milliliters measured by a bedside spirometer connected to the endotracheal tube. The calculator divides the entered value by 1000 to express it in liters.
• RSBI: The dimensionless ratio returned by the calculator, in breaths per minute per liter. The published cut-off is 105.

The tidal volume unit matters. A value entered in milliliters is divided by 1000 inside the calculator so the ratio uses the same liter denominator as the original 1991 study.

According to Yang & Tobin, NEJM 1991, a rapid shallow breathing index below 105 breaths per minute per liter was the most accurate predictor of successful weaning from mechanical ventilation in 100 medical patients.

If the same bedside read needs an oxygenation check, the A-a Gradient Calculator converts the FiO2, PaO2, and PaCO2 inputs into the alveolar-arterial gradient used alongside the RSBI on the weaning checklist.

Four concepts drive the result, and naming them keeps the value from being read as a black-box number.

The index is a ratio, not a probability, and the 105 cut-off is a single threshold from a 1991 study. Many units treat it as a screening step that decides whether to proceed with the rest of the weaning checklist. According to Physiopedia, the RSBI is measured after 30 to 120 minutes of spontaneous breathing on the ventilator with the endotracheal tube in place, and a value below 105 is the cut-off used to suggest the patient is ready for extubation.

For the acid-base half of the same blood gas, the Acid Base Calculator reads arterial pH, PaCO2, and bicarbonate into the standard base excess and anion gap outputs.

The form works from two bedside numbers. Each input should be set to the value measured on the spontaneous breathing trial, not an averaged value from the ventilator.

1. 1 Set up the spontaneous breathing trial: put the patient on a T-piece or low-level pressure support for 30 to 120 minutes with the endotracheal tube in place.
2. 2 Count the respiratory rate: watch the patient for a full minute and enter the number of breaths. The default 22 reflects a typical tachypneic value at the start of a trial.
3. 3 Measure the tidal volume: connect a bedside spirometer to the endotracheal tube or use the exhaled tidal volume from the ventilator and enter the value in milliliters.
4. 4 Read the RSBI and the band: the result panel returns the RSBI value, the tidal volume in liters, the entered rate, the breathing pattern, and the weaning interpretation band.
5. 5 Repeat across the trial: measure the ratio at the end of the trial and again partway through to see the trend. A rising ratio is usually a sign that the patient is fatiguing.

A reader at the bedside can enter respiratory rate 24 and tidal volume 450 mL, read an RSBI of about 53, and see the likely successful weaning band. The same reader can drop the tidal volume to 200 mL with the same rate and watch the index jump above 105, which mirrors what the same patient looks like as they fatigue on the trial.

When the team wants to know whether the entered tidal volume sits in the 6 to 8 mL per kg expected range, the Ideal Body Weight Calculator returns the predicted weight from height and sex in the same workflow.

Calculating the rapid shallow breathing index from two bedside inputs has several practical benefits over running the same math on a notepad at the bedside.

• • Two inputs, one number: the form turns a respiratory rate and a tidal volume in mL into a single index with the 105 cut-off, so the team can read the screening result without re-deriving the conversion.
• • Automatic liter conversion: the tidal volume is entered in milliliters and converted to liters inside the calculator, which keeps the ratio aligned with the original 1991 paper and removes a common unit error.
• • Two worked examples: the page walks through a calm trial (RR 18, Vt 500 mL) and a failing trial (RR 30, Vt 250 mL) so the result can be read against the original study.
• • Breathing pattern label: the result panel flags the rate as tachypnea, bradypnea, or normal, which keeps the same form useful for the rest of the respiratory assessment.
• • Edge handling: the calculator returns a guarded label when the entered tidal volume is 0, so the team sees a value-not-available state instead of a divide-by-zero error in the chart.
• • Same form for repeat trials: the inputs reset to the published default of 22 and 400 mL, and the same form can be reused for repeat measurements across a single weaning day.

The same form works for bedside planning, for respiratory therapy teaching, and for chart-ready documentation, and each context uses the interpretation band for a slightly different next step.

For the same ICU bedside chart, the Anion Gap Calculator reads sodium, chloride, and bicarbonate into the serum anion gap used to flag metabolic acidosis on the weaning checklist.

Four clinical factors shape the index, with caveats outside the form.

• • The 105 cut-off was derived in 1991 and is most accurate for medical ICU patients with simple weaning. Surgical, neuro, and chronic ventilator patients may need a different threshold, and newer indices have been proposed.
• • The RSBI is a screening step. The result should be paired with mental status, cough strength, secretion burden, and oxygenation before extubation.
• • The calculator is a planning and teaching aid, not a clinical device. Real weaning decisions, including whether to proceed with the trial, sit with the critical care team.

After the index is in hand, the next respiratory question is usually whether the patient is oxygenating or acidotic on the same blood gas, which is read against the A-a gradient and the arterial blood pH in the same chart.

According to NIST, the liter is defined as 1000 milliliters, so a tidal volume of 500 mL is 0.5 L for the rapid shallow breathing index formula.

When the same chart also needs the acid-base picture, the Arterial Blood pH Calculator reads pH, PaCO2, and bicarbonate from the latest arterial blood gas.