Table of Contents
Definition of Mechanical Ventilation
A method for providing assisted respiration to an individual whose lungs cannot maintain respiratory support on their own (respiratory failure). During mechanical ventilation, a machine (the ventilator) rhythmically pushes air into the lungs through an endotracheal tube or tracheostomy tube.
An endotracheal tube is a flexible plastic tube inserted through the nose or mouth into the trachea, with an inflatable cuff that holds it in place. A tracheostomy tube enters the trachea through an incision in the neck, bypassing the upper airways (including the mouth and throat). The lungs continue to do the work of oxygen-carbon dioxide exchange.
Mechanical ventilation may provide full respiratory support, in which breathing occurs only with the ventilator’s function, or partial respiratory support, in which the ventilator functions only when the person’s natural breathing is insufficient. As with normal respiration the inhalation phase of the respiratory cycle is active, with the ventilator sending air under pressure into the lungs, and the exhalation phase is passive, with the ventilator allowing the thoracic cavity’s relaxation to expel air. The ventilator typically utilizes continuous positive airway pressure (cpap), which keeps the trachea, bronchi, and bronchioles from collapsing.
There are numerous applications for, and varying levels of, mechanical ventilation. Temporary mechanical ventilation is customary after major cardiovascular or pulmonary operations and during recovery from major trauma. Other circumstances in which mechanical ventilation is a therapeutic option include
- High-level (cervical and upper thoracic) spinal cord injury that affects the nerves regulating contraction of the diaphragm and intercostal muscles (the muscles of breathing)
- Injury to the respiratory centers of the brain and brainstem
- Degenerative neurologic conditions that affect respiratory function
- Increased respiratory demands that exceed the lungs’ ability to deliver, such as in severe infections
The ventilator is primarily a mechanized bellows that fills with air (and supplemental oxygen if necessary) that inflates the lungs using positive pressure. The doctor determines the respiratory rate, air volume (amount of air the ventilator delivers), and flow pressure (pressure under which the ventilator delivers air to the person). In some situations the person does not need help with breathing but just needs an endotracheal tube or tracheostomy to protect the airway and minimize the risk of aspirating foreign matter into the lungs. In such a situation the tube may connect only to an oxygen source without a ventilator.
The Iron Lung
One of the first mechanical ventilators was nicknamed the iron lung. This device, which used a vacuum pump within a sealed chamber to cause the chest to rise, debuted during the poliomyelitis epidemics of the 1930s and 1940s. Though cumbersome (it encased the person from toes to neck), the iron lung saved countless lives.
Complications of Short-Term Mechanical Ventilation
Complications of short-term mechanical ventilation are usually minor and may include sore throat (from the endotracheal tube) and infection. Infection is a greater risk with long-term mechanical ventilation, with pneumonia being the most common.
The longer a person receives mechanical ventilation, the more difficult it becomes to wean the person to breathe independently. Long-term mechanical ventilation becomes an element of life support, which raises questions of quality of life. Doctors encourage adults to establish advance directives to help guide life-support decisions.
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