Rosh Review My EMCert Monthly Question

A 45-year-old man presents to the ED with shortness of breath that began 4 hours ago. He reports 2 days of cough, fever, and pleuritic chest pain. He is speaking in 3–4 word phrases, breathing at 33 breaths/minute, and appears in mild to moderate respiratory distress. He has right middle lobe crackles on auscultation. An arterial blood gas shows a pH of 7.48, a PaO2 of 54 mm Hg, and a PaCO2 of 33 mm Hg. What physiologic benefit does high-flow nasal cannula oxygen provide?

  1. Decreases functional residual capacity
  2. Improves carbon dioxide washout of physiologic dead space
  3. Maximizes the dilution of oxygen
  4. Provides fewer peak inspiratory flows than required


  1. Lodeserto FJ, Lettich TM, Rezaie SR. High-flow nasal cannula: mechanisms of action and adult and pediatric indications. Cureus. 2018;10(11):e3639.
  2. Möller W, Celik G, Feng S, et al. Nasal high flow clears anatomical dead space in upper airway models. J Appl Physiol. 2015;118(12):1525–1532.
  3. Riera J, Pérez P, Cortés J, Roca O, Masclans JR, Rello J. Effect of high-flow nasal cannula and body position on end-expiratory lung volume: a cohort study using electrical impedance tomography. Respir Care. 2013;58(4):589–596.
  4. Rittayamai N, Tscheikuna J, Rujiwit P. High-flow nasal cannula versus conventional oxygen therapy after endotracheal extubation: a randomized crossover physiologic study. Respir Care. 2014;59(4):485–490.


Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter/X: @srrezaie)

Cite this article as: Rosh Review Author Team, "Rosh Review My EMCert Monthly Question", REBEL EM blog, July 8, 2024. Available at:

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