5. Moderate/severe Pediatric Acute Respiratory failure of any origin evaluated after a period of respiratory stabilization (aspiration of secretions, physiotherapy, oxygen and nebulized therapy) defined as: a) Modified Silverman-Wood Downess test >or= 5 or <or= 9; b) Hypoxemic ARF(SpO2< 94% FiO2 0,5). c)Hypercapnic ARF (PaCO2 (mmHg) and/or pH <7,30)