Respiratory failure is a challenging health problem that constitutes a significant part of emergency room visits (1). Acute respiratory failure treatment is a complex process in which pharmacological and non-pharmacological methods are used in combination. Non-invasive Mechanical Ventilation (NIMV) and Invasive Mechanical Ventilation (IMV) are life-saving methods commonly used in the emergency department in severe respiratory failure (2). In patients with severe dyspnea, NIMV improves alveolar gas exchange, with very successful results in selected patients (3). However, while NIMV cannot be used in patients who are unconscious, unable to protect the airway, have upper gastrointestinal bleeding and facial trauma and cannot adapt to non-invasive mechanical ventilation, these patients have IMV indication. Both methods are quite successful when used in selected cases. Therefore, patient selection is very important for NIMV and IMV (4). It is known that endotracheal intubation increases the risk of developing complications such as ventilator-associated pneumonia and sepsis. Therefore, unnecessary endotracheal intubation and invasive mechanical ventilation therapy are expected to increase mortality (5). On the other hand, delayed intubation decision is known to be an independent risk factor for increased mortality when NIMV fails (6) (7) (8). A method that predicts NIMV failure and enables effective mortality estimation may be useful in facilitating patient selection and providing appropriate treatment to patients. There are some criteria predicting that NIMV will fail in patients with severe respiratory distress and may be guiding for early intubation. The most commonly used of these are high APACHE 2 score, ARDS or pneumonia as the etiology of respiratory distress, advanced age, and no clinical improvement after 1 hour of treatment (9). However, APECHE 2 score, which is the broadest of these criteria and includes others, is a complex scoring in which a large number of parameters are evaluated together, dependent on laboratory results and still leaves the final decision to the physician with a complete evaluation. In addition, the APACHE 2 score is a more commonly used method for intensive care patients rather than emergency patients who need a quick decision. Therefore, there is a need for a fast and practical method that can predict NIMV failure and determine early intubation decision in the management of patients admitted to the emergency department with acute dyspnea. Rapid Shallow Breathing Index (RSBI) is a parameter calculated by dividing the respiratory rate by the tidal volume and is used to predict whether patients who are intubated in intensive care unit can be extubated successfully (10). In a study by Berg et al. (11) evaluating the endotracheal intubation and mortality rates of patients who underwent NIMV, it was found that the RSBI value above 105 obtained with a single measurement was significant in predicting NIV failure. Although this result is significant, it is not sufficient to make an early intubation decision. Considering that serial measurements are found to be more meaningful than a single measurement while predicting weaning success (12), serial measurements can provide more successful results in predicting intubation and mortality of patients receiving NIMV. Although the RSBI value obtained immediately after the initiation of NIMV is high, it is possible for the patient to be relieved after the patient has been treated with NIMV for a while and thus, the RSBI value may also decrease. For this reason, after these patients have been treated for a while, obtaining RSBI value once again and looking at the patient's response to treatment may provide more meaningful results.

The aim of this study is to evaluate the success of RSBI in predicting intubation and mortality in patients presented to the emergency department with acute respiratory failure and had NIMV indication.