Application of ROX index and ROX-HR index as predictors of response to high flow nasal oxygenation in post extubation respiratory failure

In the past years, nasal high flow (NHF) oxygenation has gained popularity among intensivists to manage patients with acute respiratory failure, filling a gap in the ventilator support escalation between facemask oxygen and noninvasive or invasive mechanical ventilation. It is an attractive alternative to non-invasive ventilation (NIV) or conventional oxygen therapy because of its reported advantages in patient comfort, improved oxygenation, and decreased work of breathing in respiratory failure .

There is an increasing use of high flow nasal cannula oxygen therapy (HFNC) for acute hypoxemic respiratory failure, encouraged by evidence suggesting reduced intubation rates and possibly lower mortality .A unique feature of HFNC is its ability to comfortably deliver high flows of warmed humidified gas, 20–70 L/ min, with a FiO2 range of 0.21–1.0. Physiological responses to NHF therapy include increases in airway pressure, end-expiratory lung volume (EELV), and oxygenation which are probably optimal with higher flows (60–70 L/min), while the effects on dead-space washout, work of breathing, and respiratory rate may be obtained with intermediate flows (20–45 L/min).

The ROX (respiratory rate oxygenation) index, a ratio of pulse oximetry/fraction of inspired oxygen to respiratory rate per minute (SpO2/FiO2/RR), has been validated to predict HFNC success in patients with pneumonia and acute respiratory failure. It is easily derived from commonly recorded variables measured in a noninvasive manner. ROX-HR (respiratory rate oxygenation-heart rate) index, the ratio of ROX index over HR (beats/min) and multiplying by a factor of 100 has been tried as predictor and has shown promising resultsin the early identification of patients who are at high risk of HFNC failure and for patients initiated on HFNC for acute respiratory failure as well as a preventative strategy after a planned HFNC following extubation. However largerer validation studies are needed to establish the role of the ROX-HR index in patients on HFNC.

Extubation failure occurs in 10-20% of ICU patients and is associated with extremely poor outcomes including high mortality rates of 25 to 50% . Delayed intubation is associated with mortality. There is growing use of HFNC in post extubation failure. Although many respiratory (oxygenation, respiratory rate, thoraco-abdominal asynchrony) and non respiratory (need for vasopressors, baseline Sequential Organ Failure Assessment score, severity of disease) criteria have been found to be associated with HFNC failure, none of them has been tested prospectively to predict HFNC outcome after extubation failure. Patients identified as having a high risk of HFNC failure should be closely monitored or considered for early intubation, which may potentially improve patient outcomes.

ROX index and ROX–HR index have not been evaluated in patients with extubation failure. Therefore in this study we plan to evaluate the efficacy of ROX and ROX-HR index, in predicting HFNC failure in patients initiated on HFNC due to post-extubation respiratory failure

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