What is the RSBI?
The Rapid Shallow Breathing Index (RSBI), also known as the Yang-Tobin Index, was introduced by Karl Yang and Martin Tobin in 1991. It is the ratio of respiratory rate to tidal volume, measured during a brief period of spontaneous (unassisted) breathing. It quantifies the tendency toward rapid, shallow breathing — a pattern that strongly predicts weaning failure in mechanically ventilated patients.
The RSBI is one of the most widely used and best-validated predictors of weaning outcome in critical care medicine. It is simple to calculate at the bedside, requires no special equipment beyond a ventilator display, and can be obtained within the first 1–3 minutes of a spontaneous breathing trial.
RSBI Formula
Note: Tidal volume must be in liters. If measured in mL, divide by 1000. The result is expressed in breaths/min/L.
Interpretation & Predictive Values
| RSBI Value | Interpretation | PPV | NPV |
|---|---|---|---|
| < 105 breaths/min/L | Likely successful extubation | ~80% | — |
| ≥ 105 breaths/min/L | Likely weaning failure | — | ~95% |
In the original study by Yang and Tobin, an RSBI threshold of 105 had a sensitivity of 97%, specificity of 64%, positive predictive value of 80%, and negative predictive value of 95%. The high sensitivity and NPV mean that RSBI <105 reliably identifies patients who can be successfully extubated, while a high RSBI is a strong indicator of weaning failure.
| RSBI Range | Clinical Significance |
|---|---|
| < 80 | Very likely to wean successfully |
| 80 – 104 | Probable successful weaning; proceed with SBT |
| 105 – 120 | Borderline; consider other factors before extubation |
| > 120 | High likelihood of weaning failure; address underlying causes |
RSBI Decision Diagram
Ventilator Weaning Overview
Ventilator weaning is the process of transitioning a mechanically ventilated patient from full ventilatory support to spontaneous breathing. It accounts for approximately 40–50% of total time spent on mechanical ventilation. Timely weaning reduces ventilator-associated complications including pneumonia (VAP), diaphragm atrophy, tracheal injury, and prolonged ICU stay.
The three phases of weaning are:
- Assessment of readiness: Resolution of the acute disease, adequate oxygenation (PaO2/FiO2 >150–200), hemodynamic stability, patient able to initiate breaths, minimal vasopressor support.
- Spontaneous Breathing Trial: The patient breathes through the endotracheal tube with minimal or no ventilatory support for 30–120 minutes. RSBI is measured at the start to predict outcome.
- Extubation: Removal of the endotracheal tube if the SBT is tolerated. Post-extubation monitoring for stridor, respiratory distress, or reintubation need.
Spontaneous Breathing Trial (SBT)
An SBT can be performed using several methods:
- T-piece trial: Patient breathes through the ETT connected to a T-piece with supplemental O2. No ventilator support. Most challenging method.
- CPAP trial: Low-level CPAP (5 cmH2O) to overcome ETT resistance. Provides slight positive pressure without true ventilatory support.
- Pressure Support Ventilation (PSV): Low-level PS (5–8 cmH2O) to compensate for ETT resistance. Most commonly used method. Some argue it may overestimate readiness.
SBT failure criteria include: RR >35 for >5 min, SpO2 <90%, HR >140 or change >20%, SBP >180 or <90 mmHg, agitation, diaphoresis, or paradoxical breathing.
Extubation Criteria
Beyond RSBI, successful extubation requires assessment of several additional factors:
| Factor | Favorable for Extubation |
|---|---|
| RSBI | < 105 breaths/min/L |
| SBT duration | Tolerated 30–120 minutes without distress |
| Cough strength | Adequate cough reflex when suctioned |
| Secretions | Not excessive; suctioning needed ≤every 2 hours |
| Mental status | Alert, follows commands, GCS ≥8 |
| Cuff leak | Positive cuff leak test (suggests no significant laryngeal edema) |
| Oxygenation | PaO2/FiO2 > 150, PEEP ≤ 8 cmH2O, FiO2 ≤ 0.5 |
Worked Example
A patient on mechanical ventilation is assessed for weaning readiness. During a T-piece trial, the following measurements are obtained:
Tidal Volume = 400 mL = 0.400 L
With an RSBI of 50 (well below 105), this patient is highly likely to tolerate extubation. The SBT should continue for the full 30–120 minutes, and if no signs of distress develop, extubation is appropriate.
Frequently Asked Questions
When should RSBI be measured during the SBT?
RSBI should be measured within the first 1–3 minutes of the spontaneous breathing trial. Early measurement is important because patients who will fail often show rapid shallow breathing patterns immediately. Measuring later may miss early signs of distress that have already been compensated for.
What are the limitations of RSBI?
RSBI has several limitations: (1) It has relatively low specificity (~64%), meaning many patients with RSBI ≥105 could still be successfully extubated. (2) It was originally validated in a specific ICU population and may perform differently in other settings. (3) It does not account for cough strength, secretion management, mental status, or upper airway patency. (4) Obesity, neurological disease, and COPD may alter its predictive accuracy.
Can RSBI be used in patients with COPD?
RSBI tends to be less accurate in COPD patients because these individuals may have chronically elevated respiratory rates and lower tidal volumes at baseline. Some studies suggest using a higher threshold (e.g., 120) for COPD patients, though this is not universally adopted.
What is the difference between RSBI and other weaning predictors?
Other weaning predictors include Maximum Inspiratory Pressure (MIP ≤ -20 to -25 cmH2O), Minute Ventilation (<10 L/min), and the P0.1 airway occlusion pressure. While each has value, RSBI remains the most studied and most commonly recommended single predictor. In practice, clinicians use a combination of parameters along with clinical assessment to make weaning decisions.
What if RSBI is borderline (around 105)?
Borderline values (roughly 80–120) require careful clinical judgment. Consider the overall clinical picture including the reason for intubation, duration of mechanical ventilation, nutritional status, and comorbidities. A supervised SBT with close monitoring may still be appropriate, with a low threshold for returning to mechanical ventilation if signs of failure develop.