Tidal Volume Calculator (Lung-Protective Ventilation)
Calculate an ideal-body-weight-based tidal-volume worksheet and compare height-based targets across common ventilation contexts.
RSBI — Rapid Shallow Breathing Index Calculator
Calculate the Rapid Shallow Breathing Index (f/VT) as a spontaneous-breathing worksheet, with P/F ratio and checklist context rather than a stand-alone extubation order.
⚠️ Medical Disclaimer: RSBI is one component of ventilator weaning assessment. Clinical judgment, patient tolerance, hemodynamic stability, mental status, and airway protection must all be evaluated. Never use RSBI alone to make extubation decisions.
Measured during SBT
Spontaneous VT during SBT
Auto-calculated if blank
For P/F ratio
RSBI (f/VT)⧉
58 breaths/min/L
22 ÷ 0.38 L
Weaning Context⧉
Very likely to wean successfully
~95% success probability in classic RSBI references
P/F Ratio⧉
213
Adequate oxygenation
Minute Ventilation⧉
8.4 L/min
Acceptable
VT per kg IBW⧉
5.8 mL/kg
Adequate depth
Readiness Checklist⧉
7 / 7
Most checklist items met
RSBI = 58 — Very likely to wean successfully
Traditional reference cutoff: RSBI < 105 is commonly used as a favorable spontaneous-breathing signal.
Weaning Readiness Checklist
| Criterion | Status |
|---|---|
| RSBI < 105 | ✓ Met |
| FiO₂ ≤ 40% | ✓ Met |
| PEEP ≤ 5–8 cmH₂O | ✓ Met |
| P/F ratio ≥ 150 | ✓ Met |
| RR ≤ 35 breaths/min | ✓ Met |
| Minute ventilation ≤ 15 L/min | ✓ Met |
| VT > 5 mL/kg IBW | ✓ Met |
RSBI Interpretation
| RSBI | Interpretation | Success Rate |
|---|---|---|
| < 80 | Very favorable spontaneous-breathing pattern | ~95% |
| 80–104 | Favorable (below traditional cutoff) | ~80% |
| 105 –119 | Borderline | ~50% |
| ≥ 120 | Higher failure-risk pattern | ~20% |
Common Causes of Weaning Failure
| Category | Causes |
|---|---|
| Respiratory | Copious secretions, bronchospasm, pleural effusion, pneumonia |
| Cardiac | LV dysfunction, fluid overload, ischemia |
| Neurologic | Delirium, oversedation, ICU-acquired weakness, phrenic nerve injury |
| Metabolic | Electrolyte imbalance, malnutrition, acid-base disorder |
| Psychological | Anxiety, ventilator dependence, sleep deprivation |
Planning notes, formulas, and examples
About the RSBI — Rapid Shallow Breathing Index Calculator
The Rapid Shallow Breathing Index (RSBI), introduced by Yang and Tobin in 1991, is one of the most widely used bedside indicators during ventilator-weaning review. It is calculated as respiratory rate divided by tidal volume during spontaneous breathing, and it helps summarize whether the current breathing pattern looks efficient or rapidly shallow.
An RSBI below 105 is a classic favorable reference cutoff. That said, extubation success also depends on airway protection, secretions, neurologic status, cardiovascular stability, and the spontaneous-breathing-trial setup being used.
This calculator keeps the RSBI, oxygenation context, minute ventilation, and a simple readiness checklist together. It should be read as a structured worksheet, not as a stand-alone extubation command.
When This Page Helps
RSBI helps turn spontaneous-breathing review into a measurable bedside check on respiratory effort. By pairing respiratory rate with tidal volume and showing related readiness parameters, the calculator makes the breathing-pattern context easier to review consistently.
How to Use the Inputs
- Measure respiratory rate and tidal volume during a spontaneous breathing trial.
- Enter the ventilator mode or trial setup used.
- Add FiO₂, PEEP, and PaO₂ if you want oxygenation context.
- Review the RSBI alongside the checklist rather than by itself.
Formula used
RSBI = Respiratory Rate (breaths/min) / Tidal Volume (L)
Traditional favorable reference cutoff: < 105
Minute Ventilation = RR × VT
P/F Ratio = PaO₂ / FiO₂ (as fraction)Example Calculation
Result: RSBI = 62.9 breaths/min/L — favorable spontaneous-breathing pattern
RSBI = 22 / 0.35 = 62.9, which is below the classic 105 cutoff. The P/F ratio is 213 and minute ventilation is 7.7 L/min, so several worksheet items also sit in favorable ranges. Airway protection and full SBT tolerance would still need separate review.
Tips & Best Practices
- Measure RSBI during genuinely spontaneous breathing; even small support changes can move the number.
- Borderline values are usually more informative when trended over the full spontaneous-breathing trial.
- Read RSBI with airway protection and secretion burden in mind, not as a replacement for them.
- Use ideal body weight for VT/kg context when that convention is used locally.
Reading RSBI in Context
RSBI is strongest as a screening signal, not a full extubation decision on its own. A low index supports the idea that the patient can sustain spontaneous breathing, but airway protection, cough, secretion burden, and mental status still matter.
Borderline Values
Borderline or rising values during a spontaneous-breathing trial usually deserve more attention than a single early number. Trending the index alongside work of breathing and oxygenation is often more informative than treating one cutoff as absolute.
Why the Supporting Data Matters
Minute ventilation, tidal volume per kilogram, and the P/F ratio help explain why a patient is succeeding or failing the breathing trial. Those measures can identify fatigue, low reserve, or gas-exchange problems that RSBI alone will not capture.
Sources & Methodology
Last updated:
Methodology
This calculator computes the rapid shallow breathing index as respiratory rate divided by tidal volume in liters, then displays the result with minute ventilation, tidal-volume-per-kilogram context, and an optional P/F ratio. The checklist on the page is there to keep common readiness questions in view during a spontaneous-breathing review.
The output is intentionally framed as a worksheet. It does not decide when a patient should be extubated, because airway protection, mental status, secretion burden, hemodynamics, and the trial conditions all matter separately.
Sources
- A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation (PubMed / New England Journal of Medicine) — Original Yang-Tobin RSBI study.
- An Official American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults (PubMed / American Journal of Respiratory and Critical Care Medicine) — Guideline context for ventilator liberation and spontaneous-breathing-trial review.
Frequently Asked Questions
It is measured during spontaneous breathing, usually after the patient has been off substantial support long enough for the breathing pattern to settle. Respiratory rate is divided by tidal volume in liters.
The classic threshold is less than 105 breaths/min/L. Some units use lower cutoffs such as 80 when they want a more conservative favorable signal.
Yes. A low RSBI does not check cough strength, secretion burden, upper-airway edema, mental status, or post-extubation airway protection.
Both are used in practice, but the support level matters because pressure support can make RSBI look more favorable than a more unsupported trial.
Because extubation decisions are broader than breathing pattern alone. The checklist helps users keep oxygenation, minute ventilation, and general readiness in the same frame.
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