Rapid Shallow Breathing Index (RSBI) Calculator
The Rapid Shallow Breathing Index (RSBI), also called the Yang-Tobin index, is the ratio of respiratory frequency (f) to tidal volume (VT). Intensive care clinicians use it to gauge whether a mechanically ventilated patient is ready to be weaned from the ventilator or safely extubated. Enter the respiratory rate and tidal volume, choose your unit preference, and the calculator returns the RSBI with its clinical interpretation, including both the classic 105 threshold and the more reassuring 65 cutoff.
Formula
Worked example
A patient breathing spontaneously has a respiratory rate of 18 breaths/min and a tidal volume of 450 mL (0.45 L). RSBI = 18 / 0.45 = 40 breaths/min/L, well below the 65 threshold, indicating a highly favorable prognosis for extubation.
What is the Rapid Shallow Breathing Index?
The Rapid Shallow Breathing Index (RSBI), also called the Yang-Tobin index after the researchers who described it in 1991, is the ratio of respiratory frequency (f) to tidal volume (VT) in litres: RSBI = f / VT. It captures the pattern that patients struggling to breathe independently tend to adopt - rapid, small breaths - in a single bedside number. A high respiratory rate combined with a low tidal volume produces a large RSBI, pointing to respiratory muscle fatigue or insufficient reserve. A low RSBI reflects a slower, deeper breathing pattern consistent with adequate respiratory reserve. The index is measured during a spontaneous breathing trial (SBT) or T-piece assessment, typically while the patient breathes without pressure support for one minute with a spirometer attached to the endotracheal tube.
How to use the RSBI in clinical practice
Count or read the spontaneous respiratory rate in breaths per minute while the patient breathes without (or with minimal) ventilatory assistance. Measure the tidal volume in the same period using a handheld spirometer or ventilator flow sensor. Divide frequency by volume in litres to obtain the RSBI. In modern ICUs the values are often displayed directly by the ventilator during a pressure-support or T-piece trial. The classic threshold is 105 breaths/min/L: values below this predicted weaning success with 97% sensitivity and 64% specificity in the original cohort, while values at or above 105 predicted failure. A more stringent cutoff of 65 breaths/min/L is considered highly favorable and is associated with a very high probability of successful extubation. For patients with COPD, some evidence supports lowering the threshold to approximately 85 breaths/min/L, because their chronic airflow limitation can mask respiratory distress at values that would appear safe in a general ICU population.
Sensitivity, specificity and limitations
The original 1991 study by Yang and Tobin reported impressive predictive accuracy, but a meta-analysis of 48 later studies found only moderate sensitivity (83%) and poor specificity (58%) for the classic 105 threshold. This means the RSBI misses some patients who are truly ready (false negatives) and flags some who would succeed (false positives). Factors that can distort the result include anxiety during the measurement, secretion burden requiring suctioning, the presence and size of the endotracheal tube itself (which adds resistance), and the level of pressure support left on during assessment. Conditions like neuromuscular disease, morbid obesity, and COPD all reduce the reliability of a single RSBI measurement. For this reason, guidelines from the American Thoracic Society and European Respiratory Society recommend using RSBI as one component of a structured readiness checklist rather than as a standalone extubation criterion.
Other weaning readiness criteria to combine with RSBI
Extubation readiness involves more than a single ratio. Clinicians typically confirm: the patient is alert, cooperative, and able to follow commands; the underlying reason for intubation is resolving or resolved; oxygenation is adequate on a low fraction of inspired oxygen (FiO2 below 0.4-0.5) and minimal positive end-expiratory pressure (PEEP 5 cmH2O or less); secretion burden is manageable and the patient has an effective cough; the patient is hemodynamically stable without escalating vasopressor support; and there is no severe acid-base disturbance. A cuff leak test to rule out post-extubation stridor is also common, especially after prolonged intubation or known airway trauma. Using RSBI alongside these criteria improves clinical decision-making compared to relying on any single parameter.
RSBI interpretation thresholds
| RSBI (breaths/min/L) | Interpretation | Clinical action |
|---|---|---|
| < 65 | Highly favorable | Strong candidate - proceed if other criteria met |
| 65 to 104 | Favorable | Good candidate - confirm with full readiness checklist |
| 85 to 104 (COPD) | Borderline (COPD threshold) | Use COPD-adjusted threshold of 85 |
| 105 to 129 | Unfavorable | High risk - optimize and reassess |
| >= 130 | Weaning failure very likely | Not ready - continue ventilatory support |
Thresholds based on the original Yang-Tobin 1991 study and subsequent validation literature. COPD patients may benefit from the lower 85 breaths/min/L cutoff.
Frequently asked questions
What does the RSBI measure?
The RSBI measures the ratio of spontaneous respiratory rate (in breaths per minute) to tidal volume (in litres). It captures the pattern of rapid, shallow breathing that patients adopt when they are struggling to breathe independently. A higher RSBI reflects faster, shallower breaths and a lower respiratory reserve. The formula is simply RSBI = f / VT.
What RSBI value means a patient can be extubated?
The classic threshold from the original Yang-Tobin study is 105 breaths/min/L. Values below 105 are considered favorable and were associated with approximately 80% successful extubation in the original cohort. Values below 65 breaths/min/L are considered highly favorable and represent strong candidates for extubation. Values at or above 105 indicate a higher risk of weaning failure. For COPD patients, some guidelines use a lower threshold of 85 breaths/min/L.
How is tidal volume measured for the RSBI?
In the original method, a handheld spirometer is attached to the endotracheal tube while the patient breathes room air for one minute without any ventilator assistance. In contemporary ICUs, tidal volume is often read directly from the ventilator display during a spontaneous breathing trial at low (or zero) pressure support. Some clinicians use the average of several breaths rather than a single measurement to reduce variability.
Why is the RSBI threshold different for COPD patients?
Patients with chronic obstructive pulmonary disease often have chronically elevated respiratory rates and altered lung mechanics that allow them to compensate at rest even when their respiratory muscle reserve is limited. This means their RSBI can appear falsely reassuring. Evidence suggests that for COPD patients a lower threshold of approximately 85 breaths/min/L may better predict weaning success than the standard 105 cutoff.
Can RSBI be used as the sole criterion to extubate?
No. A meta-analysis of 48 studies found that RSBI alone has moderate sensitivity (83%) and poor specificity (58%), meaning it both misses some ready patients and flags some who would succeed. All major ventilator weaning guidelines recommend using RSBI as one data point within a comprehensive readiness checklist that also evaluates mental status, cough strength, secretion burden, hemodynamic stability, and oxygenation.
What does a very high RSBI (above 130) mean?
An RSBI above 130 breaths/min/L indicates a markedly rapid and shallow breathing pattern. The original study found that values above 105 were strongly associated with weaning failure and reintubation. At very high values, the patient is likely fatiguing or does not yet have adequate respiratory reserve to sustain unassisted breathing. Clinicians should continue ventilatory support and focus on identifying and treating the reversible factors contributing to the high RSBI.
Sources
- Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991;324(21):1445-1450.
- Meade M, Guyatt G, Cook D, et al. Predicting success in weaning from mechanical ventilation. Chest. 2001;120(6 Suppl):400S-424S. - PMC overview of RSBI validation literature.