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Abstract
BACKGROUND: The ratio of oxygen saturation index (ROX index; or SpO2/FIO2/breathing frequency) has been shown to predict risk of intubation after high-flow nasal cannula (HFNC) support among adults with acute hypoxemic respiratory failure primarily due to pneumonia. However, its predictive value for other subtypes of respiratory failure is unknown. This study investigated whether the ROX index predicts liberation from HFNC or noninvasive ventilation (NIV), intubation with mechanical ventilation, or death in adults admitted for respiratory failure due to an exacerbation of COPD.
METHODS: We performed a retrospective study of 260 adults hospitalized with a COPD exacerbation and treated with HFNC and/or NIV (continuous or bi-level). ROX index scores were collected at treatment initiation and predefined time intervals throughout HFNC and/or NIV treatment or until the subject was intubated or died. A ROX index score of ≥ 4.88 was applied to the cohort to determine if the same score would perform similarly in this different cohort. Accuracy of the ROX index was determined by calculating the area under the receiver operator curve.
RESULTS: A total of 47 subjects (18%) required invasive mechanical ventilation or died while on HFNC/NIV. The ROX index at treatment initiation, 1 h, and 6 h demonstrated the best prediction accuracy for avoidance of invasive mechanical ventilation or death (area under the receiver operator curve 0.73 [95% CI 0.66–0.80], 0.72 [95% CI 0.65–0.79], and 0.72 [95% CI 0.63–0.82], respectively). The optimal cutoff value for sensitivity (Sn) and specificity (Sp) was a ROX index score > 6.88 (sensitivity 62%, specificity 57%).
CONCLUSIONS: The ROX index applied to adults with COPD exacerbations treated with HFNC and/or NIV required higher scores to achieve similar prediction of low risk of treatment failure when compared to subjects with hypoxemic respiratory failure/pneumonia. ROX scores < 4.88 did not accurately predict intubation or death.
- ROX index
- COPD
- COPD exacerbation
- intubation
- high-flow nasal cannula
- noninvasive ventilation
- acute hypoxemic respiratory failure
- acute hypercapnic respiratory failure
Footnotes
- Correspondence: Brett Z Schaeffer MD, 4150 V Street, Suite 3100 Sacramento, CA 95817. E-mail: Bretts9113{at}gmail.com
The authors have disclosed no conflicts of interest.
This research was supported internally by the University of California, Davis (UC Davis), Division of Pulmonology and IT Health Informatics Data Center of Excellence and the UC Davis Clinical and Translational Science Center (National Center for Advancing Translational Sciences, UL1 TR000002). This study was an investigator-initiated study. The funders had no role in the study design, clinical data collection, management, analysis, interpretation of the data, manuscript preparation, and the decision to submit for publication. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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