Breathing is a spontaneous body function that exchanges carbon dioxide for oxygen. Oxygen enters the blood stream and moves to all parts of the body. When spontaneous breathing is interrupted due to injury or illness, mechanical ventilation can be used to restore this process.
There are two forms of mechanical ventilation, positive pressure and negative pressure. Positive pressure forces air into the lungs which is expelled, or exhaled, naturally when the air pressure turned off. Negative pressure creates a vacuum which forces air into the lungs. When the vacuum is stopped, exhalation occurs.
Positive pressure is the most common form of ventilation. Air pushed into the lungs is delivered by intubation. Intubation is the process of feeding a sterile tube through the nose or mouth and into the esophagus.
When a patient is intubated, a sedative will be delivered through intravenous (IV) therapy. Sedatives are used to stop patients from fighting the ventilator, which could cause damage to the lungs. Sedation may also lessen the pain and irritation of the throat or nasal passage associated with intubation.
Negative pressure is the oldest form of mechanical ventilation. The iron lung, a huge machine that stretches from the neck to the lower abdomen, was the first used in 1929 to treat breathing problems. The negative pressure used to stimulate breathing expands the abdomen which can cut off blood circulation to the lower body. Regular movement of the legs is required to stop blood from pooling in the extremities.
Iron lungs are rarely used today due to machine size and inability of the patient to move. Negative pressure, however can be a lifesaving form of ventilation. The Biphasic Cuirass is a modern form of the iron lung used in patients who cannot or should not be intubated. The cuirass machine works with the same negative pressure as the iron lung, but is much smaller and lighter.
Mechanical ventilation is meant to be a short term treatment. Injury to the airway, lungs, and pneumonia are risks associated with forced breathing. Patients are often weaned off artificial respiration slowly by using spontaneous breathing trials to judge whether the lungs will work properly without ventilation.
If needed, mechanical ventilation can continue for years with proper medical care. Patients using the iron lung in the 1940s commonly stayed in the machine for one or more years. The longer a patient uses artificial respiration, however, the harder it will be for the body to regain spontaneous breathing.