Rapid Shallow Breathing Index Calculator

Rapid Shallow Breathing Index Calculator for Critical Care. The classic threshold from Yang and Tobin is 105 breaths/min/L, often rounded to 100 in practice. Values at or below 105 identify patients likely to tolerate unassisted breathing (in the original cohort the positive predictive value for successful weaning was about 0.78 and the negative predictive value for failure about 0.95), so RSBI performs best as a rule-OUT test: a value above 105 substantially raises concern for failure. Rising or high values (>105) reflect rapid, shallow breathing from an overtaxed pump and should prompt continued support and a search for reversible loads. The index is a supporting data point, not a mandate; many patients extubate successfully after passing an SBT even when RSBI hovers near the cutoff.

How this calculator works

The Rapid Shallow Breathing Index (RSBI) is the ratio of respiratory rate to tidal volume, expressed in breaths/min per liter (f/VT). It is measured on a spontaneously breathing patient, classically during a 1-minute observation on minimal or zero support (T-piece, or CPAP/PS around zero) rather than on full ventilator settings, since pressure support and PEEP artificially lower the value. A patient breathing 30 times/min with a 0.3 L tidal volume yields an RSBI of 100. The index captures the physiologic signature of an overloaded respiratory pump: as reserve fails, patients recruit rate over depth, driving the ratio up.

When to use this calculator

Use RSBI as a screening predictor of extubation readiness in mechanically ventilated adults who have already passed the initial gate — reversal of the cause for intubation, adequate oxygenation (e.g. PaO2/FiO2 above ~150-200 on FiO2 <=0.4-0.5, PEEP <=5-8), hemodynamic stability, and intact airway protection. It is best measured at the start of a spontaneous breathing trial. Do not apply it to reintubation-risk stratification for upper-airway obstruction, to patients with chronic tracheostomy weaning, or as a stand-alone go/no-go for extubation; a good RSBI does not assess cuff leak, secretions, cough strength, or mental status.

Inputs used

  • Respiratory rate
  • Tidal volume

Clinical interpretation

The classic threshold from Yang and Tobin is 105 breaths/min/L, often rounded to 100 in practice. Values at or below 105 identify patients likely to tolerate unassisted breathing (in the original cohort the positive predictive value for successful weaning was about 0.78 and the negative predictive value for failure about 0.95), so RSBI performs best as a rule-OUT test: a value above 105 substantially raises concern for failure. Rising or high values (>105) reflect rapid, shallow breathing from an overtaxed pump and should prompt continued support and a search for reversible loads. The index is a supporting data point, not a mandate; many patients extubate successfully after passing an SBT even when RSBI hovers near the cutoff.

Worked example

A postoperative patient recovering from pneumonia is placed on a T-piece. Over one minute she takes 24 breaths with an average tidal volume of 0.40 L. RSBI = 24 / 0.40 = 60 breaths/min/L. This is well below the 105 threshold, predicting a high likelihood of successful spontaneous breathing and supporting progression to a full SBT and extubation. Contrast a patient breathing 32/min at 0.25 L: RSBI = 128, above threshold, flagging a high risk of weaning failure.

Limitations and safety notes

RSBI is measured, not automatic, so technique matters: values obtained on pressure support or CPAP run falsely low and overpredict success, so measure off support or interpret cautiously. It performs worse in specific groups — women and small-stature patients have lower tidal volumes for anatomic reasons, inflating RSBI and biasing toward false-positive failure predictions; some advocate weight-indexed or sex-adjusted cutoffs. It also misclassifies patients with neuromuscular weakness, COPD (chronic tachypnea), and those failing for non-pump reasons such as cardiac dysfunction, secretions, or delirium, none of which the ratio detects.

Frequently asked questions

Should RSBI be measured on the ventilator or off support?

Ideally off support or at near-zero settings (T-piece, or CPAP/PS close to zero). Pressure support and PEEP augment tidal volume and depress respiratory rate, driving RSBI artificially low and producing false reassurance about weaning readiness.

Is 105 an absolute cutoff for extubation?

No. It is the validated screening threshold, best used to rule out failure, not to command extubation. Passing a spontaneous breathing trial plus assessment of airway protection, cough, secretions, and mental status carries more weight than the RSBI number alone.

Why can RSBI mislead in women or smaller patients?

Tidal volume scales with body size, so smaller patients and many women generate lower VT at any given effort. This raises the ratio and can wrongly flag a capable patient as a likely weaning failure; sex- or weight-adjusted thresholds have been proposed to correct this.

Does a low RSBI guarantee successful extubation?

No. RSBI assesses only the balance between respiratory load and pump capacity. It does not evaluate airway patency, cuff leak, secretion burden, cough strength, or consciousness, all of which can cause post-extubation failure despite a favorable index.

References

  • Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991. PMID: 2023603.
  • Fan E, Zakhary B, Amaral A, et al. Liberation from Mechanical Ventilation in Critically Ill Adults. An Official ATS/ACCP Clinical Practice Guideline. Ann Am Thorac Soc. 2017. PMID: 28029806.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: May 3, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

Related reviewed calculators