Rapid Shallow Breathing Index (RSBI) Calculator

Rapid Shallow Breathing Index Explained

The RSBI (also known as the Tobin Index) is one of the criteria used in assessing the chances of successful weaning (patient still breathing on their own, 24h after extubation) from mechanical ventilation in intubated patients breathing spontaneously.

Predicting success of weaning from ventilation is crucial in reducing rates of intubation and unnecessary prolonged ventilation. Reintubation rates of 10 to 15% are typical in ICU with reintubation associated with a 7 to 11 times increase in hospital mortality.

RSBI is the ratio determined by the frequency (f) divided by the tidal volume (Vt), expressed in breaths/min/L:

RSBI = Respiratory Rate (f) in breaths/min / Tidal Volume (Vt) in L

Interpretation

Positive RSBI (<105) predicts successful extubation better than negative RSBI (>105) predicts unsuccessful extubation) so the index is more sensitive than specific.

• An RSBI <105 is considered as part of the criteria for weaning from mechanical ventilation, with 97% sensitivity for successful extubation.
• An RSBI >105 is suggestive of a high chance of failure of weaning and the patient requiring re-intubation.

It was observed that women are more likely to score an RSBI >105, independent of actual extubation outcome.

If a patient has a RSBI >105, but in all other assessments is ready for extubation, the clinician may consider potential confounding factors at play resulting in a high RSBI (for example, gemale gender, smaller endotracheal tube size or active suctioning during spontaneous breathing).

In the original study, Yang and Tobin set out to examine which physiological measurements could be used to predict successful extubation in mechanically ventilated patients. The ratio of respiratory rate and tidal volume was found to have a sensitivity of 97% and a specificity of 64%.

Verceles et al. reviewed the applicability of RSBI in patients who have been mechanically ventilated for a prolonged period of time (in their cohort – patients on mechanical ventilation for more than 21 days following tracheostomy).

No relationship was found between initial RSBI or daily RSBI and likelihood of successful weaning but the average RSBI over the entire stay was found to be statistically lower in patients with successful outcomes.

Predictors of weaning failure include advanced age, COPD, increased minute ventilation or positive fluid balance.

Other criteria for extubation

The RSBI is to be used as part of a wider assessment for the chances of successful extubation, and can accompany, for example:

• Spontaneous awakening trials (SAT) and spontaneous breathing trials (SBT) for 30 minutes.
• Oxygen saturation of 90% without arrhythmias, increase in HR and BP or respiratory distress;
• Adequacy of gas exchange.
• Absence of copious secretions.
• Strength of cough.
• Hemodynamic stability.
• Resolution/improvement of pathology that necessitated intubation.

Indices that predict successful weaning from ventilation include:

• Respiratory rate <35 breaths per minute;
• Tidal volume >5 ml/kg or >325 mL;
• FVC >15 mL/kg;
• Minute ventilation <15 L/min;
• Maximum inspiratory pressure (PImax) < -30 cmH₂.

Weaning from ventilation is typically a two-step process. First, assessment of the criteria and indices is performed, then patients should be assessed daily for their readiness to be extubed by withdrawing sedation and performing a spontaneous breathing trial. This can lead to a classification of weaning by duration:

• Simple – when ventilator is discontinued after first assessment;
• Difficult – when ventilator is discontinued 2 to 7 days after initial assessment;
• Prolonged – when ventilator is discontinued more than 7 days after initial assessment;

Higher values of RSBI tend to indicate patterns of breathing often seen in respiratory muscle fatigue, so in patients who tend to have weak inspiratory efforts and may not tolerate an SBT.

References

Original reference

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):1445-50.

Validation

Bien Udos S, Souza GF, Campos ES, et al. Maximum inspiratory pressure and rapid shallow breathing index as predictors of successful ventilator weaning. J Phys Ther Sci. 2015; 27(12):3723-7.

Verceles AC, Diaz-Abad M, Geiger-Brown J, Scharf SM. Testing the prognostic value of the rapid shallow breathing index in predicting successful weaning in patients requiring prolonged mechanical ventilation. Heart Lung. 2012; 41(6):546-52.

Other references

Esteban A, Frutos F, Tobin MJ, et al. A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group. N Engl J Med 1995; 332:345.

Epstein SK, Ciubotaru RL. Influence of Gender and Endotracheal Tube Size on Preextubation Breathing Pattern. Am J Respir Crit Care Med. 1996; 154(6 Pt 1):1647-52.

Meade M, Guyatt G, Cook D et al. Predicting success in weaning from mechanical ventilation. Chest. 2001; 120(6 Suppl):400S-24S.

Seymour CW, Cross BJ, Cooke CR, Gallop RL, Fuchs BD. Physiologic impact of closed-system endotracheal suctioning in spontaneously breathing patients receiving mechanical ventilation. Respir Care. 2009;54(3):367-74.

McConville JF, Kress JP. Weaning patients from the ventilator. N Engl J Med. 2012; 367(23):2233-2239.