Continuous Positive Airway Pressure and Oxygen Concentration on Measurement of Rapid Shallow Breathing Index

Inclusion Criteria: * intubated medical patients with mechanically ventilated more than 48 hours * clinically ready for weaning * Glasgow coma scales were at least 8 * their ventilator settings were: assist-controlled, pressure support (PS)or synchronized intermittent mandatory ventilation plus PS mode, FiO2 40% or less, positive end-expiratory pressure 5 cm H2O or less, and sensitivity setting on 1 L/min. Their arterial blood gases results were acceptable Exclusion Criteria: * having ongoing lung or neuromuscular disease and signs of increased intracranial pressure