The findings of the current study can be summarized as follows: 1) Auto-flow ventilation versus VCV had resulted in lower CVP together with higher CI and SI. 2) Blood gas analysis had demonstrated that when using auto-flow mode compared to VCV among patients with ALI/ARDS Ph was higher, PaCO2 was lower and better oxygenation estimated through better PaO2 and oxygen saturation. 3) Respiratory parameters measured had also demonstrated lower Pplat, higher tidal volumes and improvement in respiratory system compliance when auto-flow mode was used compared to VCV 4) Finally according to weaning criteria, patients ventilated with auto-flow had demonstrated higher success rate of weaning, however mortality rate and rate of re-intubation did not differ according to mode used and that patients successfully weaned had lower duration of mechanical ventilation.