ReviewThe role of high-flow oxygen therapy in acute respiratory failurePapel de la oxigenoterapia de alto flujo en la insuficiencia respiratoria aguda☆
Introduction
Acute respiratory failure (ARF) is a frequent cause of admission to Intensive Care,1 and oxygen therapy undoubtedly remains one of its first-line management options.2 Under conditions of ARF, oxygen can be administered on an invasive or noninvasive basis. However, whenever possible, we should try to avoid invasive ventilation support.
Noninvasive oxygen therapy can be administered in different ways, for example, through an oronasal mask or using nasal cannulas. However, noninvasive oxygen therapy has a number of limiting factors that condition its efficacy and therefore the correction of hypoxemia and the clinical manifestations associated to ARF. The main limiting factors are tolerance of the application system on one hand, and limitation of the administered oxygen flow on the other. The latter is generally limited to 15 l/min,3 and the flow is normally administered under conditions that do not coincide with the ideal temperature and humidity specifications (37 °C and 100% relative humidity). This limitation in administered flow implies dilution of the administered oxygen with room air, conditioned by the patient peak inspiratory flow. In this regard, the greater the peak inspiratory flow, the greater the dilution–thereby lowering the real fraction of inspired oxygen (FiO2) administered to the patient.2, 4 This situation has little impact upon patients with mild hypoxemia, though in individuals with severe ARF and important hypoxemia with peak inspiratory flows of >30 l/min, conventional oxygen therapy may not suffice to correct ARF. An alternative that would overcome these limitations of conventional oxygen therapy is the use of noninvasive mechanical ventilation (NIMV) systems–though the main problem with these systems is patient discomfort and poor tolerance of the interfaces.5
A recently introduced alternative is high-flow oxygen therapy (HFOT),6 which allows us to administer a gas flow of up to 60 l/min using silicone nasal cannulas, with ideal conditions of administered gas temperature and humidity (i.e., 37 °C and 100% relative humidity). Until a few years ago, this technique had been used mainly in newborn infants.7, 8, 9 However, its use in adult patients has increased exponentially in recent years.10
The use of HFOT affords better oxygenation through a series of different mechanisms such as reduced dilution of the administered oxygen with room air,11, 12 dead space washout,12, 13, 14 increased tidal volume15, 16 and the generation of continuous positive airway pressure (CPAP)16, 17, 18, 19. The technique could also offer benefits at hemodynamic level,20 increase patient physical exertion capacity and wellbeing,5 and improve mucociliary transport thanks to the active humidification of the administered gas.21, 22
The aim of the present study is to offer an update on the possible clinical applications of HFOT, examining the mechanisms whereby it may prove useful in adults with ARF, identifying the patients in which it may be most useful, and establishing the way in which the technique should be used.
Section snippets
Equipment
The administration of HFOT requires four elements: (1) a patient interface; (2) a high-flow administration system allowing control of the administered flow and FiO2; (3) a humidifying-warming system; and (4) non-condensing tubing (Fig. 1).
Main clinical indications
As a result of the different mechanisms of action described above, HFOT has a broad range of clinical indications.38 The main areas in which there is evidence for use of the technique are specified below. In addition, Table 1 summarizes these indications, analyzing the main studies published in the literature and the existing levels of evidence.
Starting HFOT
Table 2 summarizes the gas flows used in the different studies. In general, an initial flow of 30–40 l/min could be used. As regards FiO2, the administered level should allow us to achieve the desired arterial oxygen saturation values. On the other hand, it is important to make sure that the system reaches the appropriate temperature (37 °C) for administration of the gas.
Weaning from the system
It is difficult to establish guidelines for weaning from HFOT and its replacement by conventional oxygen therapy. However, it would seem reasonable to first lower FiO2 and then the flow.6 An acceptable recommendation could be maintenance of the administered flow until correct oxygenation is achieved with FiO2 < 0.5. The reduction in flow should be slow (5 l/min every 6–8 h). Lastly, once correct oxygenation has been achieved with ≤20 l/min and FiO2 < 0.5, we could consider switching from HFOT to
Contraindications and complications
No important adverse effects have been described in relation to the use of HFOT. Active humidification systems allow the administration of fully conditioned gas, thereby minimizing the side effects at nasopharyngeal level. In patients with chronic obstructive pulmonary disease (COPD), the use of high oxygen concentrations can cause respiratory acidosis due to the reduction of respiratory frequency and ventilation-perfusion alterations.57
A number of high-flow systems are available. The ideal
Conclusions
In sum, HFOT is a new oxygen therapy option allowing the administration of fully conditioned warmed and humidified gas at very high flow rates–improving patient oxygenation and wellbeing, and minimizing the adverse effects at nasopharyngeal level. Based on the current body of evidence, HFOT is an attractive and useful option in patients with ARF, since it improves oxygenation, lessens respiratory work, and affords improved patient wellbeing. However, further studies are needed to determine its
Conflict of interest
Fisher & Paykel collaborates with the Institut Mar d’Investigacions Mèdiques (IMIM) through a post-doctorate research grant.
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Please cite this article as: Masclans JR, Pérez-Terán P, Roca O. Papel de la oxigenoterapia de alto flujo en la insuficiencia respiratoria aguda. Med Intensiva. 2015;39:505–515.