To the Editors:
In their recent publication in the European Respiratory Journal, Confalonieri et al. 1 nicely describe relevant clinical predictive factors of noninvasive ventilation (NIV) failure in chronic obstructive pulmonary disease patients hospitalised for acute hypercapnic respiratory failure. The authors provide an interesting tool that could help to quantify this risk better and, thus, shorten the delay of a possible intubation.
NIV failures are linked to the clinical severity at admission and to the location where it was performed, as confirmed by the authors, who focused their work on clinical determinants of immediate NIV failure. However, technical factors, which are more difficult to assess, may modify the results of such prognostic studies, even if they are performed by experienced personnel. Recommendations and experts' opinions concerning NIV in the acute setting 2–4 mention the fact that a proportion of patients fail NIV because of technical problems related to humidification, interfaces, ventilatory modes and patient–ventilator interactions 4.
Humidification of inspired air is a critical factor, since heat and moisture exchangers increase the work of breathing and may lead to NIV failure 5, 6. NIV failure may also be linked to a poor adaptation to nasal/facial masks, leading to asynchrony and/or unintentional leaks. In real world studies, most teams change the interface during the ventilatory course, using facial masks to reduce leaks and, as soon as possible, nasal masks to improve tolerance 7. Finally, it would be interesting to know if the pressure support mode was modified or shifted during NIV courses in this study. A shift from pressure support to assist–control ventilation is mentioned by some authors in the literature 8, and this could help to resolve some situations, avoiding endotracheal intubation.
In addition to clinical parameters at admission, technical practices obviously need to be taken into account when assessing noninvasive ventilation success or failure during an acute hypercapnic respiratory failure episode. It is, of course, extremely difficult to design clinical studies that would control all technical factors, and we do not know to what extent such control would have modified the final message from Confalonieri et al. 1. However, since a non-negligible percentage of patients with chronic obstructive pulmonary disease and acute hypercapnic respiratory failure still fail to be successfully treated by noninvasive ventilation, the important results from Confalonieri et al. 1 would need to be extended in a prospective study assessing the role of technical factors in the outcome of acute hypercapnic respiratory failure.
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