NIV Cannot Counteract an Injurious Breathing Pattern

NIV has been proposed to prevent some of the potential complication of invasive mechanical ventilation such as ventilator-induced lung injury. However, recent data report that NIV cannot prevent its occurrence or can even facilitate it. Alveolar overdistension and alveolar recruitment and derecruitment are thought to be the two main mechanisms of ventilator-induced lung injury (VILI). Carteaux et al. recently assessed expired tidal volume in patients undergoing NIV for acute hypoxemic respiratory failure in a prospective observational study involving 62 patients [35]. They showed first that delivered tidal volumes were higher than expected and could not be controlled by the settings. In particular, the median (interquartile range) tidal volume was 9.8 mL/kg predicted body weight (8.1-11.1 mL/kg predicted body weight), although the targeted tidal volume was 6-8 mL/kg predicted body weight. Therefore, the high tidal volume was primarily driven by a high respiratory drive of the patients, and this could not be controlled by the NIV settings. In this study, high tidal volume was independently associated with NIV failure, which occurred in 51% of the cases. In the subgroup of patients with PaO₂/FiO₂ of less than 200 mmHg, a cumulative tidal volume of 9.5 mL/kg accurately predicted NIV failure with a sensitivity of 82% and a specificity of 87%. These data are remarkable with regard to the potential contributing role of high tidal volume during acute respiratory failure and NIV to a possible lung injury induced by an injurious breathing pattern. The recent FLORALI trial reported a nonsignificantly different 90-day mortality between NIV and spontaneous breathing but a lower mortality with high-flow oxygen therapy [36]. Interestingly, the authors noted that NIV administered to patients with severe lung injury could have increased the incidence of ventilator-induced lung injury by increasing tidal volumes that exceeded 9 mL/kg of predicted body weight. In clinical practice, however, tidal volume is never measured in spontaneously breathing patients, and this injurious breathing pattern may also exist without NIV. It is therefore possible that NIV should be reserved to patients without an excessive drive and able to control tidal volumes around 8 mL/kg PBW.