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.