Critically ill patients with acute respiratory failure are usually exposed to high intensity mechanical ventilation making them prone to ventilation induced lung injury. Ventilator/ventilation-induced lung injuries (VILI) result from the interaction between the ventilator delivers to the lung parenchyma and way of accepting by lung parenchyma. The ventilator-generated causes of VILI include the pressures, volume, flow, and respiratory rate. On the basis of basic thermodynamic principles, energy transfer rate (mechanical power) from ventilator to the lung tissue attributed to lung injury. If we consider the ventilatory setting, it is quite clear that tidal volume, pressures and flow are all components of the energy load, which, expressed per unit of time, is the mechanical power. Finding the correlation between mechanical power and VILI is important because Mechanical power include all the variable that have implicated in lung injury that is driving pressure, respiratory rate, tidal volume. So, in this observational study, we will review the clinical profile of the patients, calculate mechanical power and will observe the ICU mortality as primary clinical outcome of this study and the number of ventilator-free days (defined as the number of days from successful weaning to day 28, with patients who died before weaning being deemed to have no ventilator-free days), length of ICU stay and length of hospital stay will be measured as secondary outcomes. Duration of the study will be 18 months.