To what extent is the role of irv in ards?

Inverse ratio. This mode of ventilation is not used in all ards. It's efficacy is used with hopes to improve oxygenation, allowing the presence of oxygen longer for the flowing blood to pick up, mimics the new rapid collapse of the lung (expiratory phase) due to stiffness. Remember there are risks involved, and these are all temporizing measures waiting for all treatments esp antibiotics to take effect well.