Mechanical ventilation (MV) is the term for all artificial respiration procedures that use a mechanical apparatus to help or to substitute the respiratory function and that can also improve oxygenation and influence lung mechanics. Mechanical ventilation is not a therapy but a support measure that maintains the patient while an indicated structural lesion or functional disorder is corrected. Noninvasive mechanical ventilation (NIMV) is defined as external ventilatory support administered without the need for endotracheal intubation (ETI). This system has the same goals as invasive mechanical ventilation (IMV): increase or substitute the cyclic exchange of alveolar air volume produced by respiratory movements. Both therapies (NIMV and IMV), when applied to patients with respiratory failure, are aimed at achieving sufficient ventilation to maintain a proper gas exchange for the body's metabolic requirements.