Randomized controlled trial for the prevention of respiratory deterioration due to silent aspiration by transpyloric tube feeding in extremely low birth weight infants

INTERVENTION: transpyloric tube feeding group gastric tube feeding group CONDITION: Extremely Low Birth Weight Infants PRIMARY OUTCOME: Chronic lung disease, additional oxygen requirement at 36weeks post conceptional age; failure criteria,respiratory deterioration and intestinal disorder SECONDARY OUTCOME: Chronic lung disease, additional oxygen requirement at 28day of life; Mean Airway Pressure on ventilator; FiO2; FSp95,FiO2 to keep SpO2>95% at rest; RAS,Room Air Saturation ; Growth and Development INCLUSION CRITERIA: birth weight less than 1000g less than 28 weeks gestation mechanical ventilation had been performed enteral feeding had been reached 50ml/kg/day parental consent