Use of nasal high flow oxygen during acute respiratory failure

Abstract

Nasal high flow (NHF) has gained popularity among intensivists to manage patients with acute respiratory failure. An important literature has accompanied this evolution. In this review, an international panel of experts assessed potential benefits of NHF in different areas of acute respiratory failure management. Analyses of the physiological effects of NHF indicate flow-dependent improvement in various respiratory function parameters. These beneficial effects allow some patients with severe acute hypoxemic respiratory failure to avoid intubation and improve their outcome. They require close monitoring to not delay intubation. Such a delay may worsen outcome. The ROX index may help clinicians decide when to intubate. In immunocompromised patients, NHF reduces the need for intubation but does not impact mortality. Beneficial physiological effects of NHF have also been reported in patients with chronic respiratory failure, suggesting a possible indication in acute hypercapnic respiratory failure. When intubation is required, NHF can be used to pre-oxygenate patients either alone or in combination with non-invasive ventilation (NIV). Similarly, NHF reduces reintubation alone in low-risk patients and in combination with NIV in high-risk patients. NHF may be used in the emergency department in patients who would not be offered intubation and can be better tolerated than NIV.

Keywords: ARDS; Acute respiratory failure; High flow oxygen; Intubation; Nasal canula; Palliative care.

Fig. 1

Schematic representation of the physiologic effects of Nasal High Flow (NHF) and possible impact of the flow. Increase in airway pressure and FiO₂ improve oxygenation by different mechanisms and may be optimal at higher flows. Most of dead-space wash-out-related effects (increased CO₂ clearance, decrease respiratory drive, respiratory rate and effort to breathe) may be obtained for lower flows. All these physiological effects probably explain the improved comfort in patients with respiratory failure and possibly the outcomes. NHF nasal high flow, Paw airway pressure; FiO₂ fraction of inspired oxygen, EELV end-expiratory lung volume, RR respiratory rate, V_E minute volume, WOB work of breathing

Fig. 2

Suggested algorithm using the ROX index to help with intubation decision. Because the index includes in a single value three relevant respiratory parameters, the overall philosophy of the index is that if its value is increasing, the patient’s respiratory status is improving. For each time-point, there are three possibilities: (1) the patient’s ROX index is below the cut-off value, we suggest considering intubation of the patient; (2) the index is between the lower and the higher cut-off value, we suggest increasing the level of NHF (increase flow to its maximum and FiO₂ to 1) and re-evaluate after 30 min; (3) finally, if the index is above the upper boundary, we suggest pursuing NHF and close monitoring of the patient. Of note, this algorithm will require a formal validation by a RCT comparing standard of care and application of the algorithm in terms of safety and efficacy (timing of intubation)

Fig. 3

Suggested algorithm for deciding how to preoxygenate a patient with AHRF who requires tracheal intubation. NIV: non-invasive ventilation; NHF: nasal high flow; PEEP: positive-end expiratory pressure; PSV: pressure support ventilation. *The MACOCHA score can be used; **low dose vasopressor may be also started in unstable patients; ***RSI: rapid sequence induction; ****jaw thrust is essential to ensure patent upper airway and efficient apneic oxygenation