The aim of the present randomized controlled study was therefore designed to compare ASV with PSV in the weaning of COPD patients. In the current study the ASV and PSV groups were demographically comparable at the time of randomization. Factors that could affect weaning, such as respiratory parameters and severity of patients illness assessed by APACHE II score were studied in each group. The main finding of this study was that, the weaning process of COPD patients by ASV was associated with a shorter weaning duration. This was in concordance with Linton et al., who conducted weaning trials using the ASV mode and demonstrated the economy of automated weaning without the need for respiratory therapists or continuous attendance by intensivists or respiratory therapist [24].