The objective is to compare the impact of early mobilization and routine care on diaphragm thickness in critically ill children

Mechanical ventilation is a life-supporting therapy that intrinsically induces diaphragm rest. Consequently, mechanical ventilation induces time-dependent diaphragm weakness in animals and in critically ill patients, and is referred to as ventilator-induced diaphragm dysfunction (VIDD).

In most cases with VIDD, the decrease in diaphragm thickness can be detected by bedside Ultrasonography. The onset of diaphragm atrophy in the intensive care unit could be very rapid (fewer than 5 days). Vivier E. defined muscle atrophy as greater than or equal to a 10% decrease in muscle thickness on day 5 compared to day 1. It's found that diaphragm atrophy occured in 17/35 (48%). However, There is always some cases presented an increase in diaphragm thickness. Goligher EC. reported that approximately 20% of mechanically ventilated patients exhibit an increase in diaphragm thickness. In our previous study, there were about 46.7%(14/30) of ventilated children had increased diaphragmatic thickness. It's supposed that the thickening might associated with the diaphragm injury during mechanical ventilation.

Early mobilization may enhance the weaning of ventilated children, so the investigators hypothesize that the percentile of cases with increase diaphragmatic thickness will decline by early mobilization. To investigate this hypothesis, investigators are conducting a randomized trial examining the effects of early mobilization versus routine care on changing tendency of diaphragm thickness.

Enrolled children requiring mechanical ventilation will be randomized to either early mobilization group or routine care group. Diaphragm thickness will be measured by ultrasound on day1, day3, day5 and day7 after intubation and subsequently diaphragm thickness changing tendency will be calculated in each arm. The operator acquiring ultrasound images will be blinded to the care mode that the subject was randomized to. Subjects in the study will follow standard ICU sedation awakening trials and spontaneous breathing trials. The medical team in charge of the subject will determine when the subject is safe to receive early mobilization according to the standard established along with the rehabilitation team.

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

outcomes assessor and statistical analyst will be masked to randomization results