Electrical impedance tomography (EIT) has demonstrated that NHF increases both end-expiratory lung volume (EELV) and tidal volume [13, 14]. Increases in end-expiratory lung impedance (EELI) were significantly influenced by body mass index (BMI), with larger increases associated with higher BMIs. Increases in EELV may result in a reduction in the work of breathing, assist in prevention of small airway closure, and lead to improved oxygenation due to reduced shunting [13]. NHF was found to increase global EELI in both the prone and supine position, which may represent an increase in functional residual capacity [14].

One of the perceived benefits of NHF is the enhanced patient comfort and tolerability leading to improved compliance with the therapy [10, 15]. Tolerance of NHF has been demonstrated in several studies and is presumed to be due to the provision of optimal heat and humidity during the therapy to patients [10, 16, 17]. The optimal humidity delivered by the system has been shown to reduce mouth and nasal dryness when compared with dry oxygen therapy [10, 18, 19]. Also, because a nasal interface is utilized as opposed to a face mask, patients can eat, drink, sleep, and communicate more easily without removing the device. This has led to improved patient comfort, fewer removals of the interface, and less oxygen desaturation when compared with face mask oxygen therapy [20].

NHF offers a fast and sustained improvement in respiratory parameters in patients with hypoxemic respiratory failure, ensures patient comfort over extended periods of time, and has been shown to reduce respiratory rate, alleviate dyspnea, and improve oxygen saturation in adult patients presenting to the emergency department and the intensive care unit (ICU) [19, 21]. NHF can effectively be used to manage patients with mild to moderate levels of hypoxemic respiratory failure, may prevent the need for intubation, and can be used to provide respiratory support following extubation [22, 23].

NHF is a useful treatment in patients with acute respiratory failure due to a variety of causes [6, 10, 17, 19]. Evidence suggests NHF may avoid the need for intubation in patients with acute lung injury and acute respiratory distress syndrome as well as hypoxemic respiratory failure. Oxygen therapy after extubation is used to correct residual oxygen impairment. Several studies have demonstrated the use of NHF post extubation to improve gas exchange, reduce respiratory rate, improve comfort, and reduce the need for noninvasive ventilation and reintubation [15, 23, 24].

Patients who are hypoxemic, show signs of increased work of breathing, or require optimal humidity for secretion mobilization may all benefit from a trial of NHF. Patients may be electively extubated to NHF if deemed to be at increased risk for respiratory failure, for example, because of increased BMI, or NHF may be used in alternating cycles with noninvasive ventilation to rest the patient from a face mask and to provide periods for nutrition and oral care. Other indications are described in Table 17.1.