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Nasal high-flow therapy (NHFT) provides flow rates of 40 to 60 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 21.15-5). 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 of 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 deadspace 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; NHF therapy also allows for better communication, oral care, and enteral nutrition. It is suggested for use 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.
As noted above, postextubation use of NHFT may increase successful extubation, particularly in patients at a greater than minimal risk of extubation failure. In patients at higher risk, especially those with hypercapnia, postextubation noninvasive ventilation (NIV) may be preferred.
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. 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.
Lastly, NHFT may be a potential alternative in patients not tolerating noninvasive ventilation (NIV) (for example, secretions) and in such patients not requiring immediate intubation, NHFT may be tried to control dyspnea, excessive work of breathing, or hypoxia.