Goal of the study: To show that prehospital NPPV use for COPD decompensation, as compared to only standard medical treatment, might enable a decrease in intubation rate.

Primary end point: the rate of endotracheal intubation in the first three hours after randomization.

Secondary en points: rate of endotracheal intubation after third hour, rate of prehospital and ICU mortality, ICU days, effects on clinical parameters (respiratory rate, SpO2, heart rate, arterial blood pressure, consciousness) and arterial blood gases (pH, PaCO2, PaO2), 30 days mortality, delays between first medical contact and in-hospital admission, relation between initial pH level and endotracheal intubation.

Inclusion criteria: Adult patients (>18 years), with GCS≥10, known or suspected COPD and presenting acute respiratory decompensation with respiratory acidosis.

Exclusion criteria: Cardiac or respiratory arrest, upper gastro intestinal tract haemorrhage, shock, serious ventricular arrhythmia, severe sepsis, multiple organ failure, serious cranial-facial trauma, upper airways obstruction, undrained pneumothorax, uncooperative-agitated patients refusing the technique, respiratory distress with bradypnoea < 12/min, pauses gasps repeated bradycardia, intractable vomiting, acute traumatic tetraplegia, persistant hemodynamic instability with PAS<90mmHg, ensuitable environment.

Randomization: Assignment to NPPV group or standard therapy group will be performed at the time of arrival of the SAMU team to the patient, by calling a physician located at the calldispatch center who will connect to the web site of the clinical research unit from Bordeaux university hospital.

Period of study: 25 months (24 months for patients inclusion and 1 month for follow-up).

Number of patients: 199 patients in each group i.e 398 patients (significance level of 5%, power of 80%; 50% expected decrease of intubation rate, i.e. from 20 to 10%).

Main investigator: Dr Pierre-Arnaud Fort, MD, Pôle Urgences-SAMU47-Réanimation, Centre Hospitalier Saint-Esprit - Agen.

Participating centers : 20 SAMU-SMUR corresponding to 19 departments in France.

Inclusion Criteria:

• Adult patients ≥ 18 years,
• Glasgow Coma Scale (GCS) ≥ 10,
• Written consent,
• Beneficiary social security regiment,
• Known or suspected COPD,
• Acute respiratory failure with FR > 25cycles/min,
• Setting concerned of the additional respiratory muscles and/or, paradoxical abdominal breathing,
• SpO2 < 90% with oxygen or decreasing rapidly under 90% with stop oxygen,
• PaCO2 > 45mmHg and pH < 7,35.

Exclusion Criteria:

• Cardiac or respiratory arrest,
• Upper gastro intestinal tract haemorrhage,
• Shock,
• Serious ventricular arrhythmia,
• Severe sepsis,
• Multiple organ failure,
• Serious cranial-facial trauma,
• Upper airways obstruction,
• Undrained pneumothorax,
• Uncooperative-agitated patients refusing the technique,
• Respiratory distress with bradypnoea < 12/min, pauses gasps repeated bradycardia,
• Intractable vomiting,
• Acute traumatic tetraplegia,
• Persistant hemodynamic instability with PAS<90mmHg,
• Ensuitable environment,
• Acute coronary syndrome,
• Serious acute asthma,
• Acute pulmonary edema,
• Acute respiratory insufficiency with lung before healthy,
• Gas of blood non available.