The objects in sequential group who met the following criteria including those with oxygen index ( PaO2/FiO2 ) reaching 200-250 mmHg ( 1 mmHg = 0.133 kPa ) under PEEP of 8 cmH2O ( 1 cmH2O = 0.098 kPa ) , and pressure support of 12 cmH2O , and most acute infiltrating lesions having resolved on chest imaging , received noninvasive ventilation ( NIV ) immediately after extubation , and patients in control group continued to have invasive mechanical ventilation via intubation or tracheostomy with an endotracheal tube .