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.


Background: Nasal high flow (NHF) has demonstrated efficacy in relieving dyspnea in various patients with hypoxemic and hypercapnic respiratory failure. It may also reduce dyspnea in patients with acute severe asthma in the emergency department (ED). The aim of the study was to compare the efficacy of NHF with conventional oxygen therapy (COT) in improving dyspnea in acute severe asthma patients with hypoxemia in the ED.

Methods: This pilot nonblinded randomized controlled trial was conducted involving 37 patients aged ≥ 18 years with acute severe asthma and hypoxemia in the ED of Siriraj Hospital, Bangkok, Thailand (TCTR20180926003). The participants were randomly allocated to receive either COT (n = 18) or NHF (n = 19) for 120 minutes. The primary outcome was comparing the intervention effects on the patients' degree of dyspnea measured using the modified Borg scale (MBS). The secondary outcomes were comparing the interventions based on the numeric rating scale (NRS) of dyspnea, the dyspnea scale assessing accessory muscle use, vital signs, and blood gas results.

Results: The intention-to-treat analysis included 37 patients (COT group n = 18 and NHF group n = 19). The baseline mean MBS was 7.8 in both groups. At 120 minutes, the mean (±SD) MBSs in patients receiving COT and NHF were 3.3 (±2.5) and 1.4 (±2.5), respectively (mean difference = 1.9 [95% CI = 0.2 to 3.8], p = 0.043). The trends in NRS and dyspnea score results were similar to those of MBS. Respiratory rates were lower with NHF (mean difference = 4.7 [95% CI = 1.5 to 7.8], p = 0.001). No between- or within-group differences in blood gas results were found.

Conclusion: Nasal high flow reduced the severity of dyspnea and respiratory rate in hypoxemic patients with acute severe asthma in the ED.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Dyspnea / etiology
  • Dyspnea / therapy
  • Humans
  • Oxygen Inhalation Therapy*
  • Oxygen*
  • Pilot Projects
  • Thailand


  • Oxygen