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Multicenter Study
. 2023 Apr 28;24(3):511-521.
doi: 10.5811/westjem.58311.

Ratio of Oxygen Saturation to Inspired Oxygen, ROX Index, Modified ROX Index to Predict High Flow Cannula Success in COVID-19 Patients: Multicenter Validation Study

Onlak Ruangsomboon  1 , Supawich Jirathanavichai  1 , Nutthida Phanprasert  1 , Chanokporn Puchongmart  2 , Phetsinee Boonmee  3 , Netiporn Thirawattanasoot  4 , Thawonrat Dorongthom  5 , Apichaya Monsomboon  1 , Nattakarn Praphruetkit  1
Affiliations
Multicenter Study

Ratio of Oxygen Saturation to Inspired Oxygen, ROX Index, Modified ROX Index to Predict High Flow Cannula Success in COVID-19 Patients: Multicenter Validation Study

Onlak Ruangsomboon et al. West J Emerg Med. .

Abstract

Introduction: High-flow nasal cannula (HFNC) is a respiratory support measure for coronavirus 2019 (COVID-19) patients that has been increasingly used in the emergency department (ED). Although the respiratory rate oxygenation (ROX) index can predict HFNC success, its utility in emergency COVID-19 patients has not been well-established. Also, no studies have compared it to its simpler component, the oxygen saturation to fraction of inspired oxygen (SpO2/FiO2 [SF]) ratio, or its modified version incorporating heart rate. Therefore, we aimed to compare the utility of the SF ratio, the ROX index (SF ratio/respiratory rate), and the modified ROX index (ROX index/heart rate) in predicting HFNC success in emergency COVID-19 patients.

Methods: We conducted this multicenter retrospective study at five EDs in Thailand between January-December 2021. Adult patients with COVID-19 treated with HFNC in the ED were included. The three study parameters were recorded at 0 and 2 hours. The primary outcome was HFNC success, defined as no requirement of mechanical ventilation at HFNC termination.

Results: A total of 173 patients were recruited; 55 (31.8%) had successful treatment. The two-hour SF ratio yielded the highest discrimination capacity (AUROC 0.651, 95% CI 0.558-0.744), followed by two-hour ROX and modified ROX indices (AUROC 0.612 and 0.606, respectively). The two-hour SF ratio also had the best calibration and overall model performance. At its optimal cut-point of 128.19, it gave a balanced sensitivity (65.3%) and specificity (61.8%). The two-hour SF≥128.19 was also significantly and independently associated with HFNC failure (adjusted odds ratio 0.29, 95% CI 0.13-0.65; P=0.003).

Conclusion: The SF ratio predicted HFNC success better than the ROX and modified ROX indices in ED patients with COVID-19. With its simplicity and efficiency, it may be the appropriate tool to guide management and ED disposition for COVID-19 patients receiving HFNC in the ED.

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Conflict of interest statement

Conflicts of Interest: By the WestJEM article submission agreement, all authors are required to disclose all affiliations, funding sources and financial or management relationships that could be perceived as potential sources of bias. No author has professional or financial relationships with any companies that are relevant to this study. There are no conflicts of interest or sources of funding to declare.

Figures

Figure 1
Figure 1
Distribution and descriptive calibration of SF ratio, ROX, and modified ROX at 2 hours for HFNC success [A, B, C] and for overall treatment failure [D, E, F]. HFNC, high-flow nasal cannula; SF, pulse oximetry/fraction of inspired oxygen ratio; ROX, respiratory rate oxygenation index.
Figure 2
Figure 2
Calibration plots of SF ratio, ROX, and modified ROX at 2 hours for predicting HFNC success [A, B, C], and overall treatment failure (D, E, F]. HFNC, high-flow nasal cannula; SF, pulse oximetry/fraction of inspired oxygen ratio; ROX, respiratory rate oxygenation index
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