Reply to Spinelli and Mauri: Lung and Diaphragm Protection during Noninvasive Respiratory Support

We read with great interest the letter by Drs. Spinelli and Mauri discussing our recently published manuscript (1). We are grateful to the authors for their positive comments, useful suggestions for further analyses, and brilliant insights regarding interpretation of the results. We believe these remarks will foster an important debate about the role of noninvasive strategies in patients exhibiting intense inspiratory effort because of acute hypoxemic respiratory failure (2). Excessive inspiratory effort may be detrimental in hypoxemic patients because it leads to increased Vt and lung stress; causes abnormal increases in transvascular pressure and worsening lung edema; generates overstretch in the dependent lung owing to a pendelluft phenomenon; and contributes to diaphragm injury (3–5). In our study, we showed that, as compared with high-flow nasal cannula (HFNC), helmet noninvasive ventilation (NIV) is capable of reducing inspiratory effort. The decrease in inspiratory effort by helmet NIV is proportional to the degree of inspiratory effort during HFNC; accordingly, patients with low inspiratory effort while on HFNC may experience increases in transpulmonary pressure swings with helmet NIV. This suggests that monitoring of inspiratory effort would be crucial to tailor interventions and balance the benefits and harms of noninvasive strategies. Unfortunately, neither oxygenation nor respiratory rate was related to inspiratory effort in our cohort. Following the authors’ suggestion, we performed additional analyses, which showed that inspiratory effort during HFNC was weakly but significantly related to end-expiratory esophageal pressure (r = 0.64; P = 0.011). Changes in inspiratory effort and in transpulmonary pressure swings with helmet NIV were associated with this parameter as well (Figure 1). Indeed, the end-expiratory esophageal pressure reflects the lung weight, which can be increased to a variable extent according to different degrees of edema, alveolar flooding, and disease severity