How Early Mobilization Impacts on Diaphragm Thickness in Critically Ill Children

Inclusion Criteria: * subjects \> 6 months and \< 12 years of age； * subjects been intubated and mechanically ventilated for \< 24 hours at the time of screening; * the Glasgow Coma Scale (GCS) on admission of Pediatric Intensive Care Unit (PICU) is greater than 3 Exclusion Criteria: * cardiopulmonary arrest; * history of diaphragmatic paralysis or neuromuscular disease; * neuromuscular blockade; * expectation to be liberated from ventilator in \< 24 hours * history of mechanical ventilation in the last 6 months * presence of tracheostomy * high cervical spine injury * status convulsion * thoracic trauma when ultrasonic examination cannot be performed