Mechanical ventilation in the term used for assisted ventilation where oxygen is supplied to the lungs by means of artificial ways. It is done in cases when the person is unable to breath on his own. Complications are prone to occur at any point of mechanical ventilation. The ventilator associated lung injuries are as follows: 1. Barotrauma: Refers to the rupture of the pulmonary alveoli due to pressure changes along with entry of air into the surrounding alveoli (pneumothorax) or into mediastinum (pneumomediastinum). It can also result in subcutaneous emphysema. 2. Volutrauma: Overdistention of lung tissue or alveoli that damages the alveolar capillary membrane and leads to poor gas exchange. 3. Biotrauma: Damage to lung tissue as a result of activation of intense inflammatory response. 4. Atelectrauma: Refers to repeated collapse of lung alveoli during expiratory phase and expansion during inspiration that leads to alveolar damage. 5. Oxygen toxicity: High oxygen levels cause damage to lungs by various oxidative stress mechanisms.