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Positive Pressure Ventilators, Negative Pressure Ventilators

A respirator is a means to provide needed oxygen to a patient, to infuse medication directly into the lungs, or to provide the power to breathe to someone who is unable to do so on his own. A respirator may be needed following a serious trauma that interferes with the individual's breathing or for a person who has contracted a disease such as poliomyelitis that has affected the nerves that control respiration. Also, a respirator often breathes for an individual who has had surgery because the muscle relaxants that are given for the procedure may render the respiratory muscles inactive.

Respirators come in many forms. A simple tube that discharges oxygen into the nose is the simplest. This device does not breathe for the patient, but enriches his air intake with oxygen.

Other respirators are mechanical ventilators that force air into the patient's lungs or expand his chest to allow air to move into the lungs. The primary indications that an individual needs artificial ventilation are inadequate breathing on the part of the patient; that is, apnea (no breathing) or hypoventilation (lowered rate of breathing), either of which results in lowered blood oxygen (hypoxemia) levels, the second indication. These patients will have inadequate lung expansion so too little air is moved in and out, respiratory muscle fatigue, unstable respiratory drive, or they work excessively at breathing. A patient with a closed head injury may need respiratory assistance to raise the pH of the blood to an alkaline level, which helps to prevent the brain from swelling.

Persons who have chronic obstructive pulmonary disease or emphysema, either of which will become worse over time, eventually will require mechanical ventilation. Because theirs is a chronic disease process that is incurable, however, physicians hold off the assisted ventilation as long as possible. Once on the assistance device the patient will need to use it for the rest of his life.

Thus, mechanical ventilation is applied to adjust alveolar ventilation to a level that is as normal as possible for each patient, to improve oxygenation, to reduce the work of breathing, and to provide prophylactic ventilation to patients who have had surgery.

Respirators may be either positive pressure or negative pressure types. Positive pressure ventilators force air into the lungs, negative pressure machines expand the chest to suck air into the lungs.

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