Nasal High-Flow Therapy (NHFT)

Nasal high-flow therapy (NHFT) provides flow rates of 40 to 70 L/min of air. Oxygen may be added as needed to up to ~100% by using an air/oxygen blender, flow generator, and heated humidifier (see Figure: High-flow nasal cannula). The 2 main parameters that can be set are the fraction of inspired oxygen (FiO2) and inspiratory gas flow. The temperature of gas is usually set at 37 degrees Celsius, but it can be lowered to a value tolerated by the patient.

In general, patients are started with an FiO2 based on their anticipated requirements and on a flow ranging from a traditionally lower rate (~30 L/min)—which is then titrated up to the maximum tolerated flow—to a more recent higher starting rate of 50 to 60 L/min. Higher flows increase dead space washout, may produce a higher dynamic positive end-expiratory pressure (PEEP), and reduce the volume of entrained room air during the respiratory cycle, resulting in a more precise titration of FiO2. Flows are usually maintained at ~50 to 60 L/min until FiO2 requirements are lower (<50%), at which point flows are weaned alongside the FiO2.

In addition, many patients find NHFT to be more comfortable. NHFT also allows for better communication, oral care, and enteral nutrition. In addition to a standard symmetric cannula interface, an asymmetric interface has been introduced, which theoretically allows more laminar flow and better deadspace clearance during exhalation, although more evidence is needed to support its clinical impact.Evidence 1Conditional recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Moderate Quality of Evidence (moderate certainty that we know the true effect of the intervention). Quality of Evidence lowered due to imprecision. Oczkowski S, Ergan B, Bos L, et al. ERS Clinical Practice Guidelines: High-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022 Apr 14;59(4):2101574. doi: 10.1183/13993003.01574-2021. Print 2022 Apr. PMID: 34649974.

NHFT is suggested for use over conventional oxygen therapy or noninvasive ventilation (NIV) in acute hypoxemic respiratory failure, as it may reduce the risk of intubation, and is routinely used in patients with coronavirus disease 2019 (COVID-19)–related hypoxemic respiratory failure in order to avoid intubation, which is a benefit that may be further improved with the use of awake prone positioning.

Postextubation use of NHFT may increase successful extubation, particularly in patients at a greater than minimal risk of extubation failure.Evidence 2Conditional recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Moderate Quality of Evidence (moderate certainty that we know the true effect of the intervention). Quality of Evidence lowered due to imprecision. Oczkowski S, Ergan B, Bos L, et al. ERS Clinical Practice Guidelines: High-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022 Apr 14;59(4):2101574. doi: 10.1183/13993003.01574-2021. Print 2022 Apr. PMID: 34649974.  In patients at higher risk, especially those with hypercapnia, postextubation NIV may be preferred.Evidence 3Conditional recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Moderate Quality of Evidence (moderate certainty that we know the true effect of the intervention). Quality of Evidence lowered due to imprecision. Oczkowski S, Ergan B, Bos L, et al. ERS Clinical Practice Guidelines: High-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022 Apr 14;59(4):2101574. doi: 10.1183/13993003.01574-2021. Print 2022 Apr. PMID: 34649974.

While NHFT may eventually play a role in hypercapnic respiratory failure, there is currently growing but still insufficient evidence for this, especially compared with the robust body of evidence supporting the use of NIV in hypercapnia; therefore most patients with moderate to severe hypercapnia should receive a trial of NIV before using NHFT.Evidence 4Conditional recommendation (downsides likely outweigh benefits, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low certainty that we know the true effect of the intervention). Quality of Evidence lowered due to very serious imprecision. Oczkowski S, Ergan B, Bos L, et al. ERS Clinical Practice Guidelines: High-flow nasal cannula in acute respiratory failure. Eur Respir J. 2022 Apr 14;59(4):2101574. doi: 10.1183/13993003.01574-2021. Print 2022 Apr. PMID: 34649974.

NHFT can also be used for preoxygenation during endotracheal intubation; however, when used in the peri-intubation period, it may have no effect on peri-intubation hypoxemia compared with conventional oxygen delivery systems.

NHFT may be a potential alternative in patients who do not tolerate noninvasive ventilation (NIV) (eg, secretions); in such patients not requiring immediate intubation, NHFT may be tried to control dyspnea, excessive work of breathing, or hypoxia.