Mechanical ventilation restores breathing when spontaneous breathing is stopped due to injury or disease. There are two forms: positive pressure and negative pressure. Positive pressure is the most common and is delivered by intubation. Negative pressure can be life-saving and is used in patients who cannot or should not be intubated. Mechanical ventilation is a short-term treatment and patients are weaned off slowly. Prolonged use can make it harder for the body to recover spontaneous breathing.
Breathing is a spontaneous function of the body that exchanges carbon dioxide for oxygen. Oxygen enters the bloodstream and travels to all parts of the body. When spontaneous breathing is stopped due to injury or disease, mechanical ventilation can be used to restore this process.
There are two forms of mechanical ventilation, positive pressure and negative pressure. Positive pressure pushes air into the lungs which is expelled, or exhaled, naturally when the air pressure is turned off. Negative pressure creates a vacuum that pushes air into the lungs. When the vacuum is broken, exhalation occurs.
Positive pressure is the most common form of ventilation. The 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, they will be given a sedative via intravenous (IV) therapy. Sedatives are used to keep patients from fighting the ventilator, which could cause lung damage. Sedation can also reduce pain and irritation in 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 first used in 1929 to treat respiratory problems. The negative pressure used to stimulate breathing expands the abdomen which can cut off blood circulation to the lower body. Smooth leg movement is needed to keep blood from pooling in the extremities.
Iron lungs are rarely used today due to the size of the machine and the patient’s inability to move. Negative pressure, however, can be a life-saving form of ventilation. The biphasic shell is a modern form of iron lung used in patients who cannot or should not be intubated. The armor machine runs on 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 airways, lungs, and pneumonia are risks associated with forced breathing. Patients are often weaned off rescue breathing slowly using tests of spontaneous breathing to judge whether the lungs will function properly without ventilation.
If necessary, mechanical ventilation can continue for years with adequate medical care. Patients using the Iron Lung in the 1940s usually stayed in the machine for one or more years. However, the longer a patient uses rescue breathing, the harder it is for the body to recover spontaneous breathing.
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