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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.
Mechanical ventilation is one of the many things that brings forward the question of when life ends. If you've got someone hooked up to a ventilator, and it breathes for them, but they are brain dead, are they really still alive? How brain dead do they need to be? Who has the right to make that call?
I don't really have the answers, but those are questions that doctors are having to struggle with at the moment. While mechanical ventilation has been around for decades, other therapies have caught up to the point where you could maintain a brain dead patient for a lifetime. But whether or not you should be doing this is not a question that is easy to answer.
@bythewell - It really is terrible that there are still isolated pockets of polio in the world, but I don't think there is much danger of the epidemics that used to occur, at least in the Western world.
For one thing, polio is spread through poor hygiene. Most people are much better at washing their hands than they used to be. For another, we do have the knowledge of how to make vaccine even if we don't have stockpiled reserves at the moment.
Unfortunately, it is still a threat to developing nations, and the people it could hurt will probably not be able to afford mechanical ventilation if they need it. More likely, one night they will just stop breathing altogether.
I was actually just discussing with a few friends of mine the news that polio is starting to make a come back. Polio was the main reason that iron lungs were necessary back in the 40's, because children would be stricken with the disease and become unable to breath by themselves.
We had almost completely eradicated polio, the way we got rid of small pox, but it seems that there are a few villages in various places that are refusing the vaccine for whatever reason.
Unfortunately, it's difficult to prove to people who have had no education in science what a vaccine can do for you.
I just hope the iron lung doesn't have to make a comeback any time soon.