ATELECTASIS

incomplete expansion of the lungs in the newborn infant or a loss of ability to inflate the lungs, either partially or fully, because of specific respiratory disorders. There are three major types of atelectasis: congenital, compression, and obstructive atelectasis. Congenital atelectasis is seen in stillborn infants who never breathe and in children living only a few days with breathing difficulties; their lungs show areas in which the alveoli, or air sacs, are not expanded with air. These children usually suffer from a disorder called absorption atelectasis, in which the surface tension inside the alveolus is altered so that air continuously escapes through the walls, leaving the alveoli perpetually collapsed. Children with hyaline membrane disease, a disease of newborn infants associated with a failure to develop surface-active agents in the lungs, experience atelectasis from blockage of the small ducts leading to the alveoli. When a duct is blocked, the trapped air left in the alveolus is slowly absorbed by the bloodstream until the alveolus finally collapses. When a sufficiently large area is obstructed in this manner, respiratory functions cease. Compression atelectasis is caused by an external pressure on the lungs that drives the air out. Collapse is complete if the force is uniform or is partial when the force is localized. Local pressure can result from tumour growths, an enlarged heart, or elevation of the diaphragm. The ducts and bronchi leading to the alveoli are squeezed together by the pressure upon them, and air trapped in the alveoli is slowly absorbed by the blood. Obstructive atelectasis may be caused by foreign objects lodged in one of the major bronchial passageways. It may also occur as a complication of abdominal surgery. The air passageways in the lungs normally secrete a mucous substance to trap dust, soot, and bacterial cells, which frequently enter with inhaled air. When a person undergoes surgery, the anesthetic stimulates an increase in bronchial secretions. Generally, if these secretions become too abundant they can be pushed out of the bronchi by coughing or strong exhalation of air. After abdominal surgery, the breathing generally becomes more shallow because of the sharp pain induced by the breathing movements, and the muscles beneath the lungs may be weakened. Mucus plugs can result that cause atelectasis. Massive collapse of the lungs may occur a few hours to a few days after the operation. The symptoms in extreme atelectasis include laboured and painful breathing, a bluish tint to the skin, absence of respiratory movement on the side involved, displacement of the heart toward the affected side, and consolidation of the lungs into a smaller mass. If a lung remains collapsed for a long period, the respiratory tissue is replaced by fibrous scar tissue, and respiratory function cannot be restored. The treatment is directed toward removal of any obstruction, control of the infection, removal of accumulated fluids, and reestablishment of the lost pressure.