Sunday, September 15, 2019

High Flow Nasal Cannula: The Physiologic Effects

Physiologic Effects of High-Flow Nasal Cannula in Acute Hypoxemic Respiratory Failure

I have extensively covered HFNC on this page due to a talk I'm creating on the matter. We've witnessed it first hand keep patients off of the ventilator. This article published in the American Journal of Respiratory and Critical Care Medicine, which as an aside is the highest impact factor publication in the Critical Care world, looked at 15 patients to determine the physiologic effects of the HFNC system. The reason why they performed the study was because those physiologic effects that we all know are beneficial were just not defined at the time of the publication. The ambitious authors wanted to go ahead and define them. Although this study was published in May 2017, one can grasp more or less the time it takes to get one of these important studies published by noting that it was initially submitted in May 2016. Imagine having this data and not being able to get it out. I would lose my mind.
The authors used patients with a P/F ratio of less than or equal to 300. They performed a number of measurements which I will not cover here for the sake of it being Sunday morning and you do not want to be put into another nap.
In a quick and dirty recap, here are their findings:
1. less inspiratory effort
2. lighter metabolic work of breathing
3. less minute ventilation (due to decreased respiratory rate)
4. improved oxygenation
5. no change in PCO2 nor pH
6. increased lung volume in dependent and non-dependent lung regions
- this may be a huge key towards understanding the possible PEEP that the HFNC system may provide. The authors state that increasing the EELI with an improvement in oxygenation while not having a change in tidal volume may explain the PEEP effect
There are other findings which I will defer to the authors to describe in the article. Check it out in the link below.

- EJ

Link to Abstract

Mauri, T., Turrini, C., Eronia, N., Grasselli, G., Volta, C. A., Bellani, G., & Pesenti, A. (2017). Physiologic Effects of High-Flow Nasal Cannula in Acute Hypoxemic Respiratory Failure. American Journal of Respiratory and Critical Care Medicine, 195(9), 1207–1215.

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