Highlighted Paper: Application of High-flow Nasal Cannula in Hypoxemic Patients with COVID-19: A Retrospective Cohort Study
When Roca fist published his paper in June of 2019 in which he described the ROX Index for the first time, we, as of yet, had our first case of COVID-19 in the United States (which likely occurred as early as December of 2019 per current understanding at the time of this writing). That said, he described quantitative cut offs of 4.88 for HFNC success and 3.85 for HFNC failure that helped us better manage non-COVID-19 acute hypoxemic respiratory failure.
But what if these cut offs are different in COVID-19? We simply didn’t know, and many of us used the above numbers that Roca first published as a guide of how to manage COVID-19 patients on HFNC as we waited for more information to be published.
However, Hu, et al has now helped to answer this question in their publication, “Application of high-flow nasal cannula in hypoxemic patients with COVID-19: a retrospective cohort study.” In their study they found that a ROX index greater than 5.55 at 6 h after initiation was significantly associated with HFNC success (OR, 17.821; 95% CI, 3.741-84.903 p<0.001).
So where does this leave us now? I think pretty much in the same place we were before this publication, just with more confidence as more and more papers provide additional validation for the ROX Index in COVID-19 respiratory failure. What I mean by this is that few, if any, seasoned ICU doctors would look at a RSBI number and make a clinical decision to extubate without first looking at the patient and the “whole picture,” ie, labs, imaging, etc. I think this is the same with the ROX index. Though Hu et al described a higher cut off of 5.55, instead of Roca’s originally 4.88, I think the most important clinical item is that we are actually calculating the ROX index frequently on a daily basis (every 6 or 12 hours depending on the clinical context) and putting that information into context of the entire patient’s clinical picture. Doing so allows us to know, with better confidence, when we should be intubating our COVID-19 patients, and when we should continue to be conservative and hope that our patients avoid the need for mechanical ventilation.
To learn more about the ROX index please visit our website, or visit our YouTube channel to find our short video lecture on this topic.
You can also visit our website to view and download the clinical protocol we use for application of the ROX Index in our ICUs here.
References
1. Roca O, Caralt B, Messika J, Samper M, Sztrymf B, Hernández G, García-de-Acilu M, Frat JP, Masclans JR, Ricard JD. An Index Combining Respiratory Rate and Oxygenation to Predict Outcome of Nasal High-Flow Therapy. Am J Respir Crit Care Med. 2019 Jun 1;199(11):1368-1376. doi: 10.1164/rccm.201803-0589OC. PMID: 30576221.
2. https://www.nytimes.com/2020/05/15/us/coronavirus-first-case-snohomish-antibodies.html
3. Hu M, Zhou Q, Zheng R, Li X, Ling J, Chen Y, Jia J, Xie C. Application of high-flow nasal cannula in hypoxemic patients with COVID-19: a retrospective cohort study. BMC Pulm Med. 2020 Dec 24;20(1):324. doi: 10.1186/s12890-020-01354-w. PMID: 33357219; PMCID: PMC7758183.
