The primary goal of ventilator support is the maintenance of adequate, but not necessarily normal, gas exchange, which must be achieved with minimal lung injury and the lowest possible degree of hemodynamic impairment, while avoiding injury to distant organs such as the brain. Modes of MV are described by the relationships between the various types of breaths and by the variables that can occur during the inspiratory phase of ventilation. There are two basic modes of ventilation: ventilation limited by a pressure target and ventilation limited to the delivery of a specified volume.