We read with interest the paper in the July issue by Schallom et al about pressure ulcers induced by nasal-oral and full-face masks during noninvasive ventilation (NIV).

The study is attractive and almost reassuring because it shows that full-face masks are more comfortable and resulted in less pressure ulcers than nasal-oral masks. However, we detect some elements about the internal and external validity of this research that need to be further considered.

First, the staff members involved in the pressure ulcer assessment had 100% agreement, but the authors didn’t report any statistical test performed.

Second, we are concerned about the timing of skin assessment: once in the morning and once in the evening. However, we don’t know the real number of hours that passed between the evaluations. According to preclinical and clinical studies, pressure ulcers can develop in 4 to 6 hours under a sustained load and, even if...

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