Monitoring of high-flow nasal cannula for SARS-CoV-2 severe pneumonia: less is more, better look at respiratory rate
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LETTER
Monitoring of high‑flow nasal cannula for SARS‑CoV‑2 severe pneumonia: less is more, better look at respiratory rate Damien Blez1, Anne Soulier1, Francis Bonnet1, Etienne Gayat2 and Marc Garnier1* © 2020 Springer-Verlag GmbH Germany, part of Springer Nature
Dear Editor, The main clinical features of severe Corona Virus Disease 2019 (COVID-19) are hypoxaemia and respiratory failure [1]. Some COVID-19 patients may benefit from high-flow oxygen through nasal cannula (HFNC) [2]. However, it is critical not to delay intubation when it becomes necessary, otherwise increased mortality may be observed [3]. The “ROX index”, dividing the oxygen saturation by the inspired oxygen fraction and the respiratory rate (SpO2/FiO2/RR), has been proposed to monitor patients treated with HFNC [4, 5]. We conducted a monocentric prospective observational study to assess the accuracy of several parameters, including the ROX, to detect HFNC failure in the specific setting of SARS-CoV-2-related severe pneumonia. All the patients admitted in our intensive care unit with proven COVID-19 requiring HFNC during March and April 2020 were included. Clinical parameters were collected within the 4 h before, and 30 min, 2 and 6 h after HFNC initiation. HFNC was systematically initiated at 60 L min−1/FiO2 1. Then, FiO2 was decreased hourly, maintaining 92% ≤ SpO2 ≤ 98%, down to 0.4, at which point flow was progressively reduced until weaning. “HFNC failure” was defined as the need for invasive mechanical ventilation within 7 days of HFNC onset. Thirty patients were included (Table S1 in the eSupplement). Prior to HFNC, the median [IQR] RR was 30 [26–36]/min and O 2 flow was 10 [8–15] L/min. Sixteen *Correspondence: [email protected] 1 GRC 29, APHP.6, DMU DREAM, Anesthesiology and Critical Care Department, Saint‑Antoine Hospital, Sorbonne University, 184 rue du Faubourg Saint‑Antoine, 75012 Paris, France Full author information is available at the end of the article
patients met the outcome “HFNC failure” after 1 [0.9– 2.5] day. The remaining 14 patients were weaned after 5 [4–7] days. Although not different before HFNC onset, RR was significantly lower at H0.5 in the “weaned” compared to the “failure” group (24 [20–24] vs. 31 [27–34]/ min, p = 0.004). The area under the receiver operating characteristic curve (AUROC) of RR at H0.5 was 0.81 95% CI [0.61–0.96] (Fig. 1), with a best cut-off value at 26/min (sensitivity 75%, specificity 85%, positive likelihood ratio 4.9). RR at H2 and H6 was less informative (Table S2). ROX H0.5 had an AUROC of 0.78 [0.58–0.95]. Performance characteristics of ROX H0.5 using the previous published cut-off value of 4.88 [4, 5] were 81% sensitivity, 38% specificity and a positive likelihood ratio of 1.3. Neither the ROX at H2 and H6, nor its changes between H0 and H0.5, H0.5–H2, and H2–H6, had better diagnostic performance than RR at H0.5 (Tables S1 and S2). Results for the other parameters are reported in Fig. 1 and in the eSupplement. The main limitations of this derivation cohort are its monocentric
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