High Flow Nasal Cannula (HFNC) in Acute Severe Asthma Exacerbations

We all know what the standard of care is for adults who come in with acute asthma exacerbations. They receive supplemental oxygen to keep sats >92%, bronchodilators, anticholinergics, steroids, with possibly some bonus magnesium. In addition, we obtain a series of labs, chest films, and an arterial blood gas. The really sick patients have findings of both hypoxemia as well as hypercapnia (when they tire) on their ABG. This is quite concerning for the treating clinician, as well as the staff. Let’s not forget that the patient is also suffering as they cannot ventilate. I am not going to belabor what asthma is and the pathophysiology. That is beyond the scope of this post. But we should consider using high flow in asthma exacerbations. ADDENDUM: Newer article shared on 03/12/22 in the citations.

When we reach for adjunctive oxygen therapy, most clinicians attempt to place the patient on supplemental oxygen, whether a nasal cannula, venturi mask or nonrebreather or they reach for the non-invasive ventilation (NIV, which many of us cal BiPAP) as a rescue modality before having to intubate these individuals. But what is the data regarding using the high flow nasal cannula (HFNC) system in asthma? As an aside, it is also called high flow nasal oxygen (NHF or NHFO) in the cited paper.

The short answer is that there was none. Hard to believe but there is also very little data about using NIV in asthma on its own. We want to do what we can to keep these people off of the ventilator. As those of us who have managed severe asthma exacerbations on the vent know, it can be quite challenging. There are many known and extensively studied benefits to using the HFNC system in a multitude of other pathologies. Reasons for this include the fact that it provides 100% FiO2, can provide up to 60L of flow. In addition, it provides both heated and humidified air, and decreases dead space ventilation, amongst others. We have been able to keep many off of mechanical ventilation by using this technology. I personally use it every day.

Evaluating this Pilot Study on High Flow in Asthma

This study is a pilot study out of Thailand where they provided HFNC systems to patients who had severe asthma exacerbations. For those who don’t know what a pilot study is, “A small-scale test of the methods and procedures to be used on a larger scale …”. The purpose of a pilot study is to “evaluate the feasibility of recruitment, randomization, retention, assessment procedures, new methods, and implementation of the novel intervention.” (Leon et al.)

Given that this is a pilot study there are glaring limitations that must be forgiven. Obviously you cannot blind people, I mean, everyone can see the cannula on the faces of the patients. At least they did randomize the patients. The amount of patients was small with just 37, where 19 received the NHF and 18 received conventional oxygen therapy which in this study was either a standard nasal cannula or a non-rebreather for 120 minutes. The patients who were on the high-flow for their asthma exacerbations were started on a flow of 35L and that was titrated between 30-60L.

Primary Outcome: Modified Borg Score

The primary outcomes was how these patients rated their degree of dyspnea by a measurement called the modified Borg scale (MBS). The authors found that at 120 minutes, the patients in the high flow arm had less dyspnea due to their asthma exacerbation.

Secondary Outcome: Numerical Rating Scale of Dyspnea

As a secondary outcome, they used the numerical rating scale (NRS) of dyspnea which is similar to the Borg scale but they wanted another method of obtaining validity to the results. Long story short, the patients in the HFNC group also did better with this scale as well at 120 minutes.

Wrapping it up High Flow in Asthma

Now we cannot say that there’s no data looking at using high flow nasal cannula for acute asthma exacerbations. By no means is the data robust but at least we know it doesn’t cause harm. There’s much nuance to this article that I will not cover here but it is linked below, should you have the ability to access it. Unfortunately, it is not a free article. But as always, do not trust me and try to read the article for yourself. As a disclosure, I am a consultant for a company that makes high flow nasal cannula devices but they are not compensating me for this post.

CLICK HERE to learn more about HFNC
– EJ

Citations for High Flow and Asthma

Ruangsomboon O, Limsuwat C, Praphruetkit N, Monsomboon A, Chakorn T. Nasal High-flow Oxygen Versus Conventional Oxygen Therapy for Acute Severe Asthma Patients: A Pilot Randomized Controlled Trial. Acad Emerg Med. 2021 May;28(5):530-541. doi: 10.1111/acem.14187. Epub 2020 Dec 22. PMID: 33258213; PMCID: PMC8247327.
Link to Abstract

Leon AC, Davis LL, Kraemer HC. The role and interpretation of pilot studies in clinical research. J Psychiatr Res. 2011;45(5):626-629. doi:10.1016/j.jpsychires.2010.10.008
Link to Abstract

Geng W, Batu W, You S, Tong Z, He H. High-Flow Nasal Cannula: A Promising Oxygen Therapy for Patients with Severe Bronchial Asthma Complicated with Respiratory Failure. Can Respir J. 2020 Feb 20;2020:2301712. doi: 10.1155/2020/2301712. PMID: 32211084; PMCID: PMC7054795.
Link to Article

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