Expert: John Locke - 5/6/2009

Question
A mechanical ventilator breathes for a paralyzed person. During inhalation the machine forces air under the pressure into the lungs. During exhalation, the pressure drops and air moves out of the lungs. How does this machine compare with natural breathing?

Answer
Thanks for using AllExperts. Mechanical ventilation simulates, but cannot replace, normal ventilation by the lungs; there are a number of problems with long-term mechanical ventilation that relate to the physics and mechanics of the ventilators. As such, ventilation is usually started only when absolutely necessary and stopped as soon as possible.

First, ventilated patients are susceptible to a variety of respiratory infections. The ventilator bypasses the normal respiratory mechanisms for screening out inhaled pathogens and delivers air directly into the lungs, increasing the risk of pneumonia. This can be controlled for somewhat by the use of filters but it cannot be completely replaced.

In normal ventilation, the fullness of the lungs acts as a check on inspiration, but this is not present when the patient is on a ventilator. As a result, if pressures are not carefully controlled for, pneumothorax (collapsed lung) can result. Even without pneumothorax, lung alveoli can be damaged by high ventilator pressures over time.

The process of inserting or removing the endotracheal tube required for mechanical ventilation can result in damage to the airway, including the vocal cords. I know an individual who has permanent voice damage due to his being intubated. This is a definite risk of intubation if performed roughly.

I'd be happy to answer additional questions if you have them.