High-flow oxygen therapy is commonly practiced in the ICU. Recently, a method was described in which high-flow oxygen is delivered through a nasal cannula with an active humidification system that optimizes oxygen administration in patients with ARF (Optiflow, Fisher & Paykel, New Zealand). This system has several theoretical advantages. The delivery of high flows decreases dilution of the inhaled oxygen and, by matching patient's peak flow, allows accurate delivery of the set FiO2 throughout the whole inspiratory phase. In addition, a flow-dependent effect of continuous positive airway pressure, possibly due to an air entrainment mechanism, has been documented in healthy volunteers and in patients with COPD. Lastly, the use of high humidity levels may prevent damage to the ciliated epithelium of the airways, maintain mucociliary system activity, and facilitate the elimination of secretions. Through these effects, this new device for high-flow oxygen therapy has the potential to be effective and to improve tolerance to the treatment more than conventional systems for oxygen therapy, such as the Venturi mask.