There is no evidence to prefer a given ventilatory mode to provide stable support. Assisted modes are used to controlled modes because in addition to unloading of fatigued muscles, they allow some patient control over the ventilatory pattern and reduce disuse atrophy [4]. Patients with acute exacerba- tions of chronic obstructive pulmonary disease (COPD) often require either non invasive mechanical ventilation (NIMV) or invasive mechanical ventilation (IMV) and prolonged weaning times [5,6]. Although rapid weaning is preferable, there is still debate on the best weaning procedure. Pressure support venti- lation (PSV) is a common method of weaning, but it requires close patient observation for indicators of possible failure