Acute respiratory failure is one the most common reason for admission and mechanical ventilation is the most frequent procedure performed in the intensive care unit (ICU). After extubation, oxygen therapy is commonly used to correct residual impairment in oxygenation. Oxygen therapy is usually performed via a Venturi mask allowing to deliver predetermined oxygen concentrations. The face mask is used in the place of nasal cannula in part because patients with acute respiratory failure (ARF) breath preferentially through an open mouth rather than the nose. The mask may, however, reduce comfort and patients with ARF, who are often agitated and poorly cooperative, may displace or self-remove the mask. Given that oxygen delivered to the patient is dry, clinical practice guidelines recommend humidifying the oxygen when above 4 l/min in the ICU setting, because the humidification function of the nasal mucosa can be insufficient at high oxygen flow rates and/or the critically ill patient with ARF often breathes through the mouth. Breathing dry oxygen could provoke dryness of the mouth, nose, throat and respiratory tract, resulting in discomfort and pain that are frequent in the ICU setting. Breathing dry air by the nose may also lead to the alteration of the mucociliary transport system and cause an increase of airway resistance in healthy subjects. However, there are no recommendations concerning the type of humidification device to use.