Sedation for Non-invasive Ventilation in Blunt Chest Trauma

Inclusion Criteria: All blunt chest trauma patients with: * More than 3 rib fractures, pulmonary contusion, * hypoxemia or hypercapnia, or respiratory rate 20/ min despite an optimized intravenous analgesia ( paracetamol 1gm i.v. 6hourly and ketolac 30mg i.v. 8 hourly) * No indication of mechanical ventilation Exclusion Criteria: * Patients \< 18 years old, * admitted under mechanical ventilation * admitted more than 24 h after trauma or from another hospital, * patients with less than 3 ribs fractures * patients did not receive CT-scan * Patients in whom alpha-2 agonists or ketamine are contraindicated * Patients who will require an intubation during the study period for a life-threatening condition or emergency surgery or agitation as defined by a Richmond Agitation Sedation Scale (RASS) score higher than +2 will also excluded.