Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs.
Some people with respiratory failure (see Respiratory Failure) need a mechanical ventilator (a machine that helps air get in and out of the lungs) to aid breathing. Mechanical ventilation can be lifesaving.
Mechanical ventilation can be delivered many ways. Usually a plastic tube is inserted through the nose or mouth into the windpipe (trachea). If people need mechanical ventilation for more than a few days, doctors may insert the tube directly into the trachea through a small incision in the front of the neck (tracheostomy). A tracheostomy is safer and more comfortable for long-term ventilation. The tube is then attached to the ventilator. Exhalation occurs passively because of the elastic recoil of the lungs. Many types of ventilators and modes of operation may be used, depending on the underlying disorder. Depending on the person’s needs, the ventilator delivers pure oxygen or a mixture of oxygen and air.
Some people do not require complete support of their breathing. These people may be treated with a tight-fitting mask placed over the nose or nose and mouth. A mixture of oxygen and air is delivered under pressure through the mask. The pressure assists the person’s own breathing efforts and prevents fatigue of the respiratory muscles. In about half of the people with respiratory failure, this technique (called bilevel positive airway pressure or continuous positive airway pressure) can avoid the need to intubate the trachea. Use of bilevel positive airway pressure at night can help people whose respiratory failure is caused by muscle weakness, because after resting at night, the respiratory muscles are able to function more effectively during the day.
Pushing air into the lungs under too much pressure or with too high a volume can overstretch the lungs and cause lung damage. Sometimes the fragile alveoli (small air sacs in the lungs) rupture, allowing air to accumulate around the lung and collapse it, a condition called pneumothorax (see Pneumothorax). To avoid these problems, doctors try to limit the volume and pressure of air delivered by the ventilator. On the other hand, too little pressure and volume may not move enough air in and out, causing the blood to become too acidic and letting the small airways and alveoli close. Doctors constantly monitor and adjust the frequency and size of breaths delivered by the ventilator and the ventilator pressure to strike a careful balance.
Although most people undergoing mechanical ventilation need extra oxygen, too much oxygen actually can damage the lungs. Doctors monitor the person’s oxygen level to ensure that just the right amount is given.
People undergoing mechanical ventilation, particularly with intubation of the trachea, may experience agitation, which can be controlled with sedating drugs, such as propofol, lorazepam, and midazolam, or opioids, such as morphine or fentanyl. These drugs can also help relieve breathlessness.
When the trachea is intubated, bacteria from the nose and mouth can easily enter the lungs and cause serious infection. These infections must be diagnosed and treated as quickly as possible.
Because people on mechanical ventilation cannot eat, nutritional support is usually provided by giving liquid supplements through a tube positioned in the stomach.