The CPAP is a non-invasive ventilation mode most currently used CPE. It is usually obtained via a mask and an expiratory valve to maintain constant pressure in the circuit. No inspiratory assistance is provided to the patient. The BOUSSIGNAC valve is currently used in clinical practice as an adjunct to the pharmacological treatment of CPE.The effect of CPAP is mainly linked to its ability to recruit zones that are collapsed during expiration. • NIPSV combines a positive expiratory pressure to ventilatory assistance pressure during inspiration delivered by a ventilator. It corresponds to a CPAP associated with inspiratory assistance, and thus, it is likely to improve the ventilation parameters, and in particular to reduce respiratory work more efficiently than CPAP alone.These beneficial physiological effects of NIPSV were well demonstrated during the decompensation of COPD ; they wait to be confirmed during CPE. Physiological studies have shown that the NIPSV is more effective in terms of reducing the work of breathing in CPE. However, none of the 7 published randomized studies has shown superiority of the NIPSV compared to CPAP in terms of reducing mortality and intubation requirement