Physiology of Helmet vs. Facemask Noninvasive Ventilation

The optimal noninvasive management of acute hypoxemic respiratory failure is debated. Helmet noninvasive ventilation may be more effective than facemask noninvasive ventilation for these patients. Putatitve benefits of helmet use are the possibility to apply significantly higher positive end-expiratory pressure without air leaks and with good patient's comfort. In this randomized crossover study, the investigators will assess the physiological effects of helmet compared to facemask noninvasive ventilation, with the latter applied with different ventilator settings (similar to or different from helmet settings).