The study will be a prospective observational study and 64 patients with ARDS will be recruited . Written informed consent will be taken prior to inclusion of study. Study will be conducted in Medical ICU (C2 ICU) of AIIMS. Based on medical history and physical examination, radiology, biochemical and microbiological investigations etiology of ARDS will be decided.Sample will be taken at te eime of admission for estimation of inflammatory markers hsCRP,IL-1.IL-6,TNF ,Procalcitonin.From the available variables APACHE II, Sequential organ failure assessment score (SOFA), Simplified acute physiological score (SAPS)II and 3 will be calculated to assess the severity of ARDS.All patients will be given mechanical ventilation using the protocol followed by the ARDS Network low-tidal volume ventilation strategy.The data will be registered on ICU admission and there after every 24 hr. Day 0 will be defined as the interval from the time of ICU admission to 8:00 am the next day .Every day data will be recorded at a fixed time at 9 am. It will include Tidal volume Vt (ml/kg),respiratory rate/min, Minute ventilation(l/min),FiO2,PaO2/FiO2,Inspiratory flow(I:E), Ppeak (cm of H2O),Static respiratory compliance(ml/cm of water).Plateau pressure (Pplat), Peak end expiratory pressure (PEEP).Patient will be monitored throughout the course of illness and the outcome of ARDS will be assessed.