Low Dose Morphine to Relieve Dyspnea in Acute Respiratory Failure (OPIDYS)

Randomized, double-blind, placebo-controlled, parallel-group, single-center phase 2 pilot study.The experimental group will receive an intravenous titration of morphine followed by a subcutaneous administration of morphine hydrochloride for 24 hours according to a predefined protocol. The control group will receive placebo NaCl 0.9% administered according to the same protocol as the experimental arm Patients will be randomized 1:1 between low-dose titrated morphine (experimental group) and placebo (control group). The other treatments will be similar in both groups, according to the protocol and the recommendations. Severe dyspnea will be assessed for regularly Patients will be followed for 48 hours: 24-hour treatment duration, evaluation of primary endpoint for first 24 hours, collection of adverse events for 48 hours.