From the Guidelines
The Respiratory Severity Body Index (RSBI) is not explicitly defined in the provided evidence, however, a similar concept, the Rapid Shallow Breathing Index (RSBI), is mentioned as a measure to predict the need for intubation in patients receiving noninvasive ventilation (NIV), with an RSBI > 105 breaths/min/L associated with the need for intubation 1.
Definition and Calculation
The Rapid Shallow Breathing Index (RSBI) is calculated by dividing a patient's respiratory rate by their tidal volume in liters (RR/VT) 1.
Clinical Application
An RSBI value is used to assess the likelihood of successful weaning from mechanical ventilation or the need for intubation in patients on noninvasive ventilation. An RSBI > 105 breaths/minute/liter suggests the patient may require intubation, while values below this threshold may indicate a lower need for invasive ventilation 1.
Measurement and Interpretation
To measure RSBI, clinicians typically assess a patient's spontaneous breathing pattern, often over one minute, after briefly disconnecting them from the ventilator. This index is valuable because it objectively quantifies the patient's breathing efficiency, with patients having rapid, shallow breaths (high RSBI) working harder to breathe and likely not ready for extubation or may require closer monitoring and potential intubation 1.
Clinical Decision Making
While RSBI is a useful tool in ventilator management decisions, it should be considered alongside other clinical parameters such as oxygen requirements, mental status, ability to protect the airway, and overall clinical stability 1. The physiological basis for RSBI's effectiveness is that it reflects respiratory muscle strength, endurance, and the work of breathing required by the patient.
Key Considerations
- Close monitoring is essential for patients on noninvasive support, as deterioration can occur abruptly 1.
- Positive responses to noninvasive support are usually evident soon after initiation, and if there is no substantial improvement in gas exchange and respiratory rate within a few hours, invasive mechanical ventilation should be considered without delay 1.
From the Research
Definition and Purpose of RSBI
- The Rapid Shallow Breathing Index (RSBI) is a widely used predictor for weaning from mechanical ventilation 2, 3, 4, 5, 6.
- It is calculated as the ratio of respiratory rate to tidal volume, and is used to evaluate a patient's readiness for extubation.
Measurement Techniques and Variations
- RSBI can be measured using different techniques, including manual calculation with a Wright spirometer and automated calculation using ventilator-derived values 3, 6.
- The level of ventilator support, such as continuous positive airway pressure (CPAP), can affect RSBI values 3, 4.
- The time of day at which RSBI is measured does not appear to significantly affect the results 3.
Predictive Accuracy and Thresholds
- RSBI has been shown to be a good predictor of weaning outcome, with optimal thresholds ranging from 72 to 97 breaths/min/L 2, 5.
- The accuracy of RSBI in predicting weaning outcome can be affected by various factors, including the patient's underlying condition and the specific ventilatory strategy used 4.
- Receiver operating characteristic (ROC) curve analysis can be used to determine the optimal RSBI threshold for predicting weaning success 2, 5.
Comparison of Measurement Techniques
- Studies have compared the accuracy and reliability of different RSBI measurement techniques, including manual calculation with a Wright spirometer and automated calculation using ventilator-derived values 6.
- The results of these studies suggest that the average RSBI value calculated from multiple time points may provide the best correlation with the standard technique 6.