The main job of our lungs is to get oxygen into the body and to get rid of carbon dioxide. When a patient's lungs are no longer able to do this job completely, we use a mechanical ventilator to help. Most commonly, patients are put on a mechanical ventilator when they are in respiratory failure. Respiratory failure is the situation when the patient has a low level of oxgyen in the blood, even while getting oxygen therapy or when the level of carbon dioxide rises too much in the blood. Some patients need help from a mechanical ventilator even though they still have nearly normal levels of oxygen and carbon dioxide in the bloodstream. This can be true when breathing is very uncomfortable. Sometimes patients are placed on a mechanical ventilator because of other serious injuries that require treatment, which may interfere with breathing temporarily.
In most cases, mechanical ventilators are used for patients who cannot breathe by themselves. The only other choice would be to allow the patient to die, while using respiratory medicines to maintain comfort. Mechanical ventilators do not actually fix diseases, but rather keep the patient alive while the hospital staff finds out why the patient has difficulty breathing and treats the disease that is causing the difficulty.