Non-invasive ventilatory support and high-flow nasal oxygen as first-line treatment of acute hypoxemic respiratory failure and ARDS

Abstract

The role of non-invasive respiratory support (high-flow nasal oxygen and noninvasive ventilation) in the management of acute hypoxemic respiratory failure and acute respiratory distress syndrome is debated. The oxygenation improvement coupled with lung and diaphragm protection produced by non-invasive support may help to avoid endotracheal intubation, which prevents the complications of sedation and invasive mechanical ventilation. However, spontaneous breathing in patients with lung injury carries the risk that vigorous inspiratory effort, combined or not with mechanical increases in inspiratory airway pressure, produces high transpulmonary pressure swings and local lung overstretch. This ultimately results in additional lung damage (patient self-inflicted lung injury), so that patients intubated after a trial of noninvasive support are burdened by increased mortality. Reducing inspiratory effort by high-flow nasal oxygen or delivery of sustained positive end-expiratory pressure through the helmet interface may reduce these risks. In this physiology-to-bedside review, we provide an updated overview about the role of noninvasive respiratory support strategies as early treatment of hypoxemic respiratory failure in the intensive care unit. Noninvasive strategies appear safe and effective in mild-to-moderate hypoxemia (PaO₂/FiO₂ > 150 mmHg), while they can yield delayed intubation with increased mortality in a significant proportion of moderate-to-severe (PaO₂/FiO₂ ≤ 150 mmHg) cases. High-flow nasal oxygen and helmet noninvasive ventilation represent the most promising techniques for first-line treatment of severe patients. However, no conclusive evidence allows to recommend a single approach over the others in case of moderate-to-severe hypoxemia. During any treatment, strict physiological monitoring remains of paramount importance to promptly detect the need for endotracheal intubation and not delay protective ventilation.

Keywords: Acute hypoxemic respiratory failure (AHRF); Acute respiratory distress syndrome (ARDS); Continuous positive airway pressure (CPAP); High-flow nasal oxygen (H-FNO); Inspiratory effort; Noninvasive ventilation (NIV); Patient self-inflicted lung injury (P-SILI); Pressure support ventilation (PSV); Transpulmonary pressure.

Fig. 1

Summary of the mechanisms of patient self-inflicted lung injury

Fig. 2

Benefits and risks of the tools for non-invasive respiratory support in AHRF/ARDS. PSV pressure support ventilation, CPAP continuous positive airway pressure, PS pressure support, P_L, transpulmonary pressure, HME heat and moisture exchanger

Fig. 3

Mechanisms of action of standard oxygen therapy, HFNO, CPAP and PSV-NIV in a representative patient with AHRF. Tracings of pressure at airway opening (P_AW, a continuous pressure 3 cmH₂O is assumed for HFNO [80]), inspiratory flow, esophageal pressure (P_ES) and dynamic transpulmonary pressure (P_L, calculated as P_AW − P_ES) are displayed. P_ES negative deflection during inspiration is the inspiratory effort (ΔP_ES). P_L positive deflection is the dynamic transpulmonary driving pressure (ΔP_L), which is an estimate of the static transpulmonary driving pressure [121]