Using the ROX Index to Predict Treatment Outcome for High-Flow Nasal Cannula and/or Noninvasive Ventilation in Patients With COPD Exacerbations

Brett Z Schaeffer; Sarina A Fazio; Jacqueline C Stocking; Jason Y Adams; Anna Liu; Hugh B Black; Richart W Harper; Irene Cortes-Puch; Timothy E Albertson; Brooks T Kuhn

doi:10.4187/respcare.11544

Using the ROX Index to Predict Treatment Outcome for High-Flow Nasal Cannula and/or Noninvasive Ventilation in Patients With COPD Exacerbations

Respir Care. 2024 Apr 23:respcare.11544. doi: 10.4187/respcare.11544. Online ahead of print.

Authors

Affiliations

¹ Division of Pulmonary, Critical Care, and Sleep Medicine, University of California, Davis, Davis, California; and Veterans Affairs Northern California Healthcare System, Mather, California. Bretts9113@gmail.com.
² Center for Nursing Science, UC Davis Health, Sacramento, California.
³ Division of Pulmonary, Critical Care, and Sleep Medicine, University of California, Davis, Davis, California.
⁴ Division of Pulmonary, Critical Care, and Sleep Medicine, University of California, Davis, Davis, California; and Data Center of Excellence, UC Davis Health, Sacramento, California.
⁵ Data Center of Excellence, UC Davis Health, Sacramento, California.
⁶ Division of Pulmonary, Critical Care, and Sleep Medicine, University of California, Davis, Davis, California; and Veterans Affairs Northern California Healthcare System, Mather, California.

PMID: 38653556
DOI: 10.4187/respcare.11544

Abstract

Background: The ratio of oxygen saturation index (ROX index; or S_pO₂ /F_IO₂ /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.

Keywords: COPD; COPD exacerbation; ROX index; acute hypercapnic respiratory failure; acute hypoxemic respiratory failure; high-flow nasal cannula; intubation; noninvasive ventilation.