Chest
Volume 148, Issue 1, July 2015, Pages 253-261
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Contemporary Reviews in Critical Care Medicine
Heated Humidified High-Flow Nasal Oxygen in Adults

https://doi.org/10.1378/chest.14-2871Get rights and content

Traditionally, nasal oxygen therapy has been delivered at low flows through nasal cannulae. In recent years, nasal cannulae designed to administer heated and humidified air/oxygen mixtures at high flows (up to 60 L/min) have been gaining popularity. These high-flow nasal cannula (HFNC) systems enhance patient comfort and tolerance compared with traditional high-flow oxygenation systems, such as nasal masks and nonrebreathing systems. By delivering higher flow rates, HFNC systems are less apt than traditional oxygenation systems to permit entrainment of room air during patient inspiration. Combined with the flushing of expired air from the upper airway during expiration, these mechanisms assure more reliable delivery of high Fio2 levels. The flushing of upper airway dead space also improves ventilatory efficiency and reduces the work of breathing. HFNC also generates a positive end-expiratory pressure (PEEP), which may counterbalance auto-PEEP, further reducing ventilator work; improve oxygenation; and provide back pressure to enhance airway patency during expiration, permitting more complete emptying. HFNC has been tried for multiple indications, including secretion retention, hypoxemic respiratory failure, and cardiogenic pulmonary edema, to counterbalance auto-PEEP in patients with COPD and as prophylactic therapy or treatment of respiratory failure postsurgery and postextubation. As of yet, very few high-quality studies have been published evaluating these indications, so recommendations regarding clinical applications of HFNC remain tentative.

Section snippets

Search Criteria

We searched for publications and abstracts on PubMed, the Cochrane Database of Systematic Reviews, and Scopus using the search terms “high flow” OR “humidified” OR “heated” AND “oxygen therapy” OR “nasal oxygen.” We limited the search to English-language publications but did not limit the search based on publication type. We searched for both bench studies and adult human studies. We considered only studies defining nasal high flow as a flow rate ≥ 20 L/min.

Potential Mechanisms of Clinical Benefit

HFNC consists of high-flow gas with an Fio2 ranging from 0.21 to nearly 1.0 adjusted by an oxygen blender, brought to body temperature, and saturated with water through an in-line humidifier. The gas mixture is then provided to the nares through loose-fitting nasal prongs that are slightly larger but softer than those used for standard nasal oxygen therapy. The mechanisms by which HFNC may offer advantages to patients with dyspnea and hypoxemia are shown in Table 1.

Hypoxemic Respiratory Failure

HFNC has been tried in a number of different types of hypoxemic respiratory failure (Table 2). Initially, a few anecdotal cases were reported on the comfort and oxygenation advantages of HFNC in respiratory failure and during procedures such as bronchoscopy in patients with hypoxemia.44, 49, 50, 51 Two retrospective analyses showed significant improvement in oxygenation and reduction in respiratory rate in adult burn patients52 and in a surgical high-dependency unit.53

In 2010, Roca et al5

Possible Role for HFNC in the Treatment of Hypoxemia and Respiratory Failure

Based on the multiple physiologic and subjective benefits of HFNC compared with standard oxygen therapy, HFNC is assuming a role in the management of hypoxemia and respiratory failure. The greatest benefit appears to be in patients who have severe hypoxemia and would ordinarily receive standard high-flow oxygen therapy by mask. For these patients, HFNC offers enhanced comfort, more-reliable delivery of Fio2, and more-efficient ventilation. HFNC is unlikely to benefit patients with more mild

Practical Application

Because of the limited clinical data available for adult applications of HFNC, it is difficult to make firm recommendations on practical aspects of HFNC use. Physiologic studies have demonstrated that the beneficial effects of HFNC are related to flow rate, so we prefer to initiate therapy by adjusting this parameter first and then to titrate the Fio2 to maintain target oxygenation. Flow rates on commercially available devices range from 5 to 60 L/min. Studies in the literature have started

Conclusions

Devices that deliver high-flow heated and humidified oxygen through nasal cannulae (HFNCs) have become a standard of care in several clinical situations for infants, children, and preterm neonates. By virtue of a number of physiologic benefits over conventional oxygen therapy, including greater comfort and tolerance, more-effective oxygenation in some circumstances, and improved breathing pattern with increased tidal volume and decreased respiratory rate and dyspnea, we are now seeing

Acknowledgments

Financial/nonfinancial disclosures: The authors have reported to the following conflicts: Dr Hill has served on the Medical Advisory Board and received consulting fees from Fisher Paykel and has also received consulting fees from Vapotherm. Drs Spoletini, Alotaibi, and Blasi have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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