COVID-19 Evidence Alerts
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Clinical Prediction Guide Vega ML, Dongilli R, Olaizola G, et al. COVID-19 Pneumonia and ROX index: Time to set a new threshold for patients admitted outside the ICU. Pulmonology. 2021 May 7. pii: S2531-0437(21)00092-1. doi: 10.1016/j.pulmoe.2021.04.003.
Abstract

High flow nasal cannula (HFNC) is used to treat acute hypoxemic respiratory failure (AHRF) even outside the ICU and the ROX index (pulse oximetry/fraction of inspired oxygen/respiratory rate) may predict HFNC failure.

OBJECTIVE: The purpose of this investigation was therefore to verify whether the ROX index is an accurate predictor of HFNC failure for COVID-19 patients treated outside the intensive care unit (ICU) and to evaluate the validity of the previously suggested threshold.

DESIGN: Multicenter study. Retrospective observational analysis of prospectively collected data.

SETTING: 3 centres specialized in non-invasive respiratory support (Buenos Aires, Argentina; Bolzano and Treviso, Italy). Patients treated outside the ICU were analysed MEASUREMENTS: The variables to calculate the ROX index were collected during the first day of therapy at 2, 6, 12 and 24 hours and then recorded every 24 hours. HFNC failure was defined as escalation of respiratory support to invasive mechanical ventilation (IMV) or death.

MAIN RESULTS: A total of 35 (29%) patients failed HFNC and required intubation. ROC analysis identified the 12-hour ROX index as the best predictor of intubation with an AUC of 0.7916[CI 95% 0.6905-0.8927] and the best threshold to be 5.99[Specificity 96% Sensitivity 62%]. In the survival analysis, a ROX value <5.99 was associated with an increased risk of failure (p?=?0008?log - rank test). The threshold of 4,9 identified by Roca as the best predictor in non-COVID patients, was not able to discriminate between success and failure (p?=?0.4?log-rank test) in our patients.

CONCLUSIONS: ROX index may be useful in guiding the clinicians in their decision to intubate patients, especially in patients with moderate ARF, treated therefore outside the ICU. Indeed, it also demonstrates a different threshold value than reported for non-COVID patients, possibly related to the different mechanisms of hypoxia.

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Comments from MORE raters

Respirology/Pulmonology rater

It is evident that we must expect a higher COX index in more severe patients. In fact, the calculated higher index in this study compared with that of Roca is just due to the difference in spectrum of patients and it didn't mean that we must set a new threshold.

Respirology/Pulmonology rater

Retrospective look at ROX index (SpO2/FiO2)/RR as a predictor of transition from NPPV to intubation in hospitalized Covid-19 patients. No mention of prone positioning of patients, which may reduce the need for intubation. Will need prospective evaluation to see if generally applicable.