Background: High-flow nasal cannula (HFNC) may help avoid intubation of hypoxemic patients suffering from COVID-19; however, it may also contribute to delaying intubation, which may increase mortality. Here, we aimed to identify the predictors of HFNC failure among patients with COVID-19.Methods: We performed a multicenter retrospective study in China from January 15 to March 31, 2020. Two centers in Wuhan (resource-limited centers) enrolled 32 patients, and four centers outside Wuhan enrolled 34 cases. HFNC failure was defined as the requirement of escalation therapy (NIV or intubation). The ROX index (the ratio of SpO2/FiO2 to the respiratory rate) was calculated.Results: Among the 66 patients, 29 (44%) cases experienced HFNC failure. The ROX index was much lower in failing patients than in successful ones after 1, 2, 4, 8, 12, and 24 h of HFNC. The ROX index was independently associated with HFNC failure (OR = 0.65; 95% CI: 0.45–0.94) among the variables collected before and 1 h after HFNC. To predict HFNC failure tested by ROX index, the AUC was between 0.73 and 0.79 for the time points of measurement 1–24 h after HFNC initiation. The HFNC failure rate was not different between patients in and outside Wuhan (41% vs. 47%, p = 0.63). However, the time from HFNC initiation to intubation was longer in Wuhan than that outside Wuhan (median 63 vs. 22 h, p = 0.02). Four patients in Wuhan underwent intubation due to cardiac arrest; in contrast, none of the patients outside Wuhan received intubation (13 vs. 0%, p = 0.05). The mortality was higher in Wuhan than that out of Wuhan, but the difference did not reach statistical significance (31 vs. 12%, p = 0.07).Conclusion: The ROX index can be used to predict HFNC failure among COVID-19 patients to avoid delayed intubation, which may occur in the resource-limited area.

The purpose of this study is to observe the potential of lung ultrasound in evaluating the severity of coronavirus disease 2019 (COVID-19) pneumonia. Lung ultrasound was performed in ten zones of the patients' chest walls. The features of the ultrasound images were observed, and a lung ultrasound score (LUS) was recorded. The ultrasound features and scores were compared between the refractory group (PaO 2 /FiO 2 ≤ 100 mm Hg or on extracorporeal membrane oxygenation) and the non-refractory group. The prediction value of the LUS was studied by receiver operating characteristic (ROC) curve analysis. In total, 7 patients were enrolled in the refractory group and 28 in the non-refractory group. B-line patterns and shred signs were the most common signs in all patients. Patients in the refractory group had significantly more ground-glass signs (median 6 [interquartile range {IQR}, 2.5–6.5] vs. median 0 [IQR, 0–3]), consolidation signs (median 1 [IQR, 1–1.5] vs. median 0 [IQR, 0–3]) and pleural effusions (median 5 [IQR, 1.5–6] vs. median 0 [IQR, 0–0.25]). The LUS was significantly higher in the refractory group (33.00 [IQR 27.50–34.00] vs. 25.50 [IQR 22.75–30.00]). The ROC of the LUS showed a cutoff score of 32 with a specificity of 0.893 and a sensitivity of 0.571 in diagnosing refractory respiratory failure among patients. In COVID-19 patients, lung ultrasound is a promising diagnostic tool in diagnosing patients with refractory pneumonia.

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