Pediatric atresia of the lung

　　1. Etiology

　　Atresia of the lung is common in children, which can be caused by various reasons leading to the collapse or lack of air in lung tissue, resulting in the loss of normal function. It can also be divided into three categories according to its etiology:

　　1, External force compression

　　Compression of the lung substance or bronchus can have the following 4 situations:

　　（） Thoracic movement disorder: Abnormalities of nerves, muscles, and bones, such as cerebral palsy, poliomyelitis, polyneuritis, spinal muscular atrophy, myasthenia gravis, and skeletal deformities (vitamin D deficiency disease, pectus excavatum, scoliosis). Multiple neuritis is most common in Beijing.

　　(2) Diaphragmatic movement disorder: Due to phrenic nerve palsy or increased intraperitoneal pressure. It is often caused by large amounts of ascites due to various reasons.

　　(3) Limitation of lung expansion: Due to reduced intrathoracic negative pressure or increased pressure, such as pleural effusion, pneumothorax, empyema, hemothorax, chylous pleurisy, tension pneumothorax, diaphragmatic hernia, tumor, and cardiac enlargement, etc.

　　(4) External force compression of the bronchus: Due to compression by enlarged lymph nodes, tumors, vascular rings, or cysts, the bronchial lumen is blocked, and air cannot enter the lung tissue. The enlarged left atrium and pulmonary artery can compress the left main bronchus, leading to left lung atelectasis. A common case at Beijing Children's Hospital is pulmonary atelectasis caused by bronchial lymph node tuberculosis of the tumor type; there have also been 2 cases of children with high ventricular septal defects, where the left ventricular blood directly enters the pulmonary artery through the defect, causing the pulmonary artery to dilate and compress the left main bronchus, leading to complete atelectasis of the entire left lung.

　　2, Obstruction in the bronchus or bronchioles

　　The bronchial lumen can be blocked in the following situations:

　　(1) Foreign bodies: Foreign bodies blocking the bronchus or bronchioles can cause lobar or segmental atelectasis. Occasionally, foreign bodies blocking the trachea or main bronchus can cause bilateral or unilateral atelectasis.

　　(2) Bronchial lesions: Tracheobronchial softening, airway stenosis, submucosal tuberculosis, tuberculosis granuloma, diphtheria pseudomembrane extending to the trachea and bronchi, bronchiectasis, etc.

　　(3) Spasm of the bronchial wall and obstruction of the airway by thick secretions: The respiratory tract of infants is narrow and easily blocked. Inflammation of the lungs, such as pneumonia, bronchitis, whooping cough, measles, cystic fibrosis, ciliary dyskinesia, immune deficiency, chronic lung disease in newborns, and after repair of esophageal atresia, as well as in the case of bronchial asthma, the bronchial mucosa swells, smooth muscle spasms occur, and thick secretions can block the respiratory tract, causing atelectasis. Such causes are more common in winter and spring, so the incidence of atelectasis is also higher in cold seasons. Cough suppressants such as opium and atropine can reduce natural coughing and make secretions thicker, both of which can worsen obstruction, so they should not be used excessively. When the diaphragm and chest muscles are hypotonic or even paralyzed due to poliomyelitis or other causes, bronchial secretions are not easily expectorated. In the case of chest surgery, prolonged general anesthesia, deep anesthesia, or traumatic shock, due to stimulation causing bronchospasm, and since bronchial secretions are already increased, if the cough reflex is suppressed or disappears, secretions are more likely to block the airway, causing atelectasis. In the case of bronchiolitis, interstitial pneumonia, and bronchial asthma, obstruction of many small bronchi often occurs. Initially, it presents as obstructive emphysema, and later, some become completely obstructed, forming atelectasis, coexisting with emphysema. The formation of obstructive atelectasis can be elucidated based on the results of bronchoscopy.

　　3. Non-obstructive atelectasis

　　In addition to the above two types, in recent years, there has been increasing attention to non-obstructive atelectasis, the main reason for which is:

　　(1) Deficiency of surfactant: Surfactant is produced by type II alveolar epithelial cells and is a phospholipoprotein complex, with dipalmitoyl lecithin being the main component. Surfactant lines the inner surface of the alveoli and has the function of reducing the surface tension at the gas-liquid interface of the alveoli, stabilizing the alveoli to prevent atelectasis. If surfactant is deficient, the surface tension of the alveoli increases, the recoil force of the alveoli increases, and the alveoli collapse, causing many areas of microatelectasis. Deficiency of surfactant can be seen in: ① Immature lung development in premature infants. ② Bronchopneumonia, especially viral pneumonia, which leads to a decrease in surfactant production. ③ Initial stages of trauma, shock, and other conditions that cause excessive ventilation, rapidly consuming surfactant. ④ Inhalation of toxic gases or pulmonary edema, which can destroy and denature surfactant. The normal surface tension of the lung is 6 dyn/cm², while in the case of surfactant deficiency, the surface tension of infants with respiratory distress syndrome can reach 23 dyn/cm².

　　(2) Another type of non-obstructive atelectasis may be related to the neuromuscular structure of the terminal airways of the lung: Many scholars have confirmed that there is a muscle elastin fiber, which is a combination of smooth muscle and elastic fibers, from the airways to the alveolar ducts and alveolar sacs, and it is controlled by the autonomic nervous system. During severe pain such as rib fractures and surgery, or when the bronchus is strongly stimulated, such as during bronchial angiography, the contraction of the muscle elastin fiber can cause atelectasis, especially in large areas of lung collapse.

　　(3) Shallow breathing: This can be seen in patients after surgery and administration of morphine, as well as in patients in a coma or in a state of extreme weakness. When the pressure within the lungs decreases to a level insufficient to resist local surface tension, it can gradually lead to the closure of alveoli and atelectasis. Encouraging deep breathing in postoperative patients can prevent the closure of alveoli, or can allow the alveoli that have closed due to shallow breathing to reopen. In summary, atelectasis is more common in children, and its causes include bronchiolitis, bronchitis, asthma, bronchial lymph node tuberculosis, polyneuritis, bronchial foreign bodies, and more after surgery. In addition, it can also be seen in aspiration pneumonia, bronchiectasis, intracranial hemorrhage, endocardial elastosis, congenital heart disease, tumors, and other conditions.

　　2. Pathogenesis

　　1. Bronchial obstruction

　　It first causes obstructive emphysema, leading to gas accumulation in the alveoli, which is gradually absorbed by the blood and results in alveolar collapse. The extent of collapse is affected by the development of Kohn holes between alveoli and the communication tract between bronchioles and alveoli, Lambert's tubes. Therefore, the younger the child, the more common atelectasis, and the larger the scope. The blood perfusion in the atelectatic area has little impact, so the ventilation/perfusion ratio changes, resulting in right-to-left shunting and varying degrees of hypoxemia. Obstruction causes secretions to accumulate and stagnate in the tracheal lumen, promoting bacterial proliferation. Accumulation of secretions in the alveoli, and sometimes the volume of the atelectatic segment is larger than normal, this condition is called 'drowned lung'. Secretions are absorbed within 36 hours, and the segment shrinks. Compensatory hyperinflation of alveoli or emphysema appears around the atelectasis.

　　2. Non-obstructive atelectasis

　　It is seen in reduced pulmonary ventilation, spasm of alveolar smooth muscle elastic fibers, and deficiency of surface tension active substances in alveoli.

　　Compensatory hyperinflation of alveoli may occur, and in severe cases, emphysema may form. If atelectasis persists for a long time, it is easy to develop secondary infection on the basis of atelectasis, causing bronchial damage and retention of inflammatory secretions. Over time, bronchiectasis, lung abscess, or pulmonary fibrosis may occur. Pulmonary fibrosis refers to the lung interstitial tissue composed of collagen, elastin, and glycoproteins. When fibroblasts are damaged chemically or physically, they secrete collagen to repair the lung interstitial tissue, thereby causing pulmonary fibrosis; that is, the result of human repair after lung injury.

　　1. Symptoms and signs

　　Due to different etiologies and the size of the area, the manifestations are also different. The following describes the atelectasis of different ranges separately.

　　1. Unilateral or bilateral lung atelectasis

　　It often occurs due to various reasons, such as paresis of the chest muscles, diaphragm, disappearance of the cough reflex, and obstruction of bronchial secretions, resulting in unilateral or bilateral lung atelectasis. The onset is very acute, and breathing is extremely difficult. Older children can report chest pain and palpitations, and may have high fever, tachycardia, and cyanosis. In patients who have undergone surgery, it often occurs within 24 hours after surgery. The following are obvious chest signs:

　　(1) The chest wall on the same side is flatter, and respiratory movement is restricted

　　(2) The trachea and apex beat deviate towards the affected side

　　(3) There is slight dullness on percussion, but it can be obscured by the rising stomach on the left side

　　(4) Weak or absent vocal resonance and breath sounds

　　(5) Elevation of the diaphragm.

　　2. Lobar atelectasis

　　The onset is slower, and respiratory distress is less common. The signs are similar to unilateral atelectasis of the lung, but the degree is lighter and can vary with the atelectatic lung lobe. When the upper lobe is atelectatic, the trachea shifts to the affected side without the heart moving, and the dullness on percussion is limited to the anterior chest; when the lower lobe is atelectatic, the trachea does not shift and the heart moves to the affected side, and the dullness on percussion is located near the spine on the back; when the middle lobe is atelectatic, the signs are fewer and difficult to detect, often not obvious on percussion due to compensatory emphysema in the adjacent area.

　　3. Segmental atelectasis

　　Clinical symptoms are rare and not easily noticeable. Atelectasis can occur in any lobe or segment of the lung, but it is most rare in the left upper lobe. Only when there is congenital heart disease, the dilated left pulmonary artery can compress the left upper lobe bronchus, causing atelectasis of the left upper lobe. The most common site of pediatric atelectasis is the lower lobes of both lungs and the middle lobe of the right lung; atelectasis is more common in the left lower lobe and right middle lobe during lower respiratory tract infection; enlarged lymph nodes due to tuberculosis often cause atelectasis in the right upper and middle lobes; 'middle lobe syndrome' (middlelobesyndrome) refers to atelectasis of the middle lobe caused by tuberculosis, inflammation, asthma, or tumor, which is long-lasting, recurrently infected, and can eventually develop into bronchiectasis.

　　2. Pulmonary function test

　　It can be seen that there is a decrease in pulmonary functional capacity, a decrease in lung compliance, an abnormal ventilation/perfusion ratio, varying degrees of arteriovenous shunting, and hypoxemia.

　　3. X-ray examination

　　The X-ray characteristics are uniform and dense shadows, occupying one side of the chest, a lobe or segment of the lung, with no structure in the shadow, disappearance of pulmonary vessels, and reduction in lobe volume. When there is atelectasis on one side or a large area, the intercostal space can become narrower, the thoracic cavity can become smaller, and the position of the shadow varies with the location of atelectasis in different lobes of the lung. The lower lobe atelectasis appears as a triangular shadow in the anteroposterior chest film, located between the spine and diaphragm, and close to the posterior chest wall in the lateral film. If it is upper lobe atelectasis, both the anteroposterior and lateral shadows are wedge-shaped, with the tip pointing downwards and towards the hilum. If it is atelectasis of the right middle lobe, the anteroposterior shadow is triangular, with the base at the right edge of the heart shadow and the tip pointing laterally; the lateral shadow is wedge-shaped, with the base near the anterior chest wall, above the diaphragm, with the tip pointing backwards and upwards. In infancy, except for compensatory emphysema, other compensatory phenomena such as displacement of the trachea and heart and elevation of the diaphragm may not appear temporarily and may only occur after a long duration of atelectasis. However, due to insufficient surfactant, microatelectasis often presents as a ground-glass shadow, and the X-ray manifestations are indistinguishable from those of lobar pneumonia.

　　4. Course of the disease

　　Obstructive atelectasis can be transient or persistent. The atelectasis caused by mucus plug or mucosal edema due to pneumonia, bronchiolitis, asthma, and bronchitis has a short duration and can easily disappear after inflammation and swelling are removed. When tuberculosis or unremoved foreign bodies are present, atelectasis can be persistent, and bilateral or large-area atelectasis often leads to rapid death. Immediate bronchoscopy to remove the obstructive material and artificial respiration rescue are required to survive.

　　Mainly for the prevention of respiratory tract infection and the aspiration of foreign bodies. One of the effective methods to prevent upper respiratory tract infection in children is to enhance the immunity of the respiratory tract and strengthen the resistance of children to pathogens. The following measures can be taken: advocate breastfeeding. Breast milk is the most ideal natural food for infants, containing various nutrients. Breast milk contains a large amount of immunoglobulins, immune cells, lysozyme, lactoferrin, and other substances that help enhance the anti-infection ability of infants. Especially the colostrum secreted in the first few days after childbirth, which is rich in antibodies and trace elements, especially SIGA, is helpful in preventing respiratory and gastrointestinal infections.

　　1. X-ray examination

　　The X-ray chest film shows a uniform dense shadow, occupying one side of the chest or a lobe or lung segment. The shadow has no structure, the lung markings disappear and the volume of the lung lobe decreases. In the early stage of 'suffocated lung', the chest film shows the extension of the interlobar fissure, with visible increased volume of segments or lung lobes, and the pleural line changes from the normal straight line to convex; 36 hours later, the atelectasis area collapses, the interlobar fissure becomes concave, and the most typical is the atelectasis of the right middle lobe, which collapses into a uniform dense band, easily misdiagnosed as pleural thickening. Unilateral atelectasis of the lung is caused by complete obstruction of the main bronchus on one side, with the lung field on the affected side showing a uniform dense shadow, accompanied by collapse of the thoracic cage, narrowing of the intercostal spaces, shift of the trachea, mediastinum, and heart to the affected side, elevation of the diaphragm, and compensatory emphysema in the opposite lung, large lobe atelectasis caused by complete obstruction of the lobar bronchus, with shrinkage of the lung lobe volume and a dense uniform shadow, the interlobar fissure shows concentric displacement. When the right upper lobe is atelectatic, the anterior-posterior chest film shows increased density of the right upper lobe, the lateral fissure shifts upwards outside, the volume of the upper lobe shrinks into a fan shape, and the slightly contracted upper lobe fissure appears as a concave-underside arc. The significantly contracted upper lobe can be manifested as a triangular dense shadow located adjacent to the mediastinum with the tip pointing towards the hilum and the base at the apex of the lung. The mid-lower lung fields show obvious upward and scattered lung markings, with the hilum elevated. The mid-lower lobes develop compensatory emphysema, and the trachea can shift to the right. The left upper lobe, as it includes the lingula, is thicker at the top and thinner at the bottom. When atelectatic, the posterior-anterior film shows a blurred shadow in the middle zone of the left upper and middle lung fields, with higher density at the top and lighter at the bottom, without clear boundaries. The trachea shifts to the left, and the lateral film shows the oblique fissure shifting forward. The lower lobe shows compensatory emphysema, and its dorsal segment can expand upwards to the level of the second thoracic vertebra. When the right middle lobe is atelectatic, the anterior-posterior film shows a patchy blurred shadow below the right hilum, with the tip pointing towards the lung field and the base narrowing at the hilum. The lateral view shows a strip or a long triangular shadow tilting downwards from the hilum. When both lower lobes are atelectatic, their X-ray manifestations are similar, showing a triangular dense shadow with the tip pointing upwards and the base downwards in the inner side of both lower lung fields, with the hilum shadow shifting downwards. The upper and middle lobes have compensatory emphysema, with lung markings shifting downwards and becoming scattered. The right lower lobe atelectasis is more obvious than the left, and the left lower lobe atelectasis may not be visible due to the overlap of the heart shadow. In oblique or overexposed X-ray films, the atelectasis of the lower lobe often shows the oblique fissure shifting downwards and backwards, with reduced translucency in the lower lobe area. Large lobe atelectasis often complicates with varying degrees of secondary phenomena, such as narrowing of the intercostal spaces on the same side, elevation of the diaphragm on the same side when the lower lobe collapses, upward shift of the hilum when the upper lobe is atelectatic, and downward shift when the lower lobe is atelectatic (under normal circumstances, the hilum on the left side is slightly higher than that on the right). The mediastinum and heart contours shift towards the affected side. The mediastinal structure in infancy has elasticity, especially evident. In children and adults, atelectasis of the upper lobe may cause the trachea to shift towards the affected side, but the normal trachea in infants is longer and bends to the right, so if tracheal shift is seen alone, it has little diagnostic significance in infancy. The healthy part of the lung on the affected side and the compensatory emphysema in the opposite lung enhance the translucency. It is common for the opposite lung to herniate through the upper part of the mediastinum to the affected side. The anterior-posterior film of segmental atelectasis generally shows a wedge-shaped dense shadow, with the tip pointing towards the hilum and the base outward. Subsegmental atelectasis is patchy, with the X-ray showing a horizontal strip.Located above the dome of the diaphragm, visible in both anteroposterior and lateral positions. During asthma attacks, many segmental atelectasis appear, presenting as diffuse streaky shadows, easily mistaken for pneumonia. After asthma is controlled within 1 to 2 days, the shadow disappears on re-examination. Circular disk-shaped atelectasis is uncommon, being spiral-shaped, with X-ray showing circular, oval, angular, or comma-shaped shadows, often occurring at the base of the lung, secondary to pleural effusion or therapeutic pneumothorax, hence often accompanied by pleural thickening, blunting of the costodiaphragmatic angle, collapse of the hemithorax, or pleural calcification. It needs to be differentiated from malignant tumors. Transparent membrane disease presents with typical reticular granules, indicating overexpansion of small airways and air spaces. If it appears as a uniform non-transparent area, it indicates the expansion of atelectatic areas.

　　2. Pulmonary function test

　　Visible reduction in lung volume, decreased lung compliance, abnormal ventilation/perfusion ratio, varying degrees of arteriovenous shunting, hypoxemia, and so on.

　　3. CT scan

　　Chest CT scan shows atelectasis of lung segments.

　　4. Fiberoptic bronchoscopy examination

　　It can clearly identify the blocked site, can perform cytological and histological examination, can perform bacterial quantitative culture and drug sensitivity analysis, can perform local medication, and has diagnostic and therapeutic significance.

　　1. It is recommended to eat more foods that enhance immunity, such as mushrooms, monkey head mushrooms, straw mushrooms, black fungus, silver ear, choy sum, lily, etc.

　　2. The principle should be to invigorate the lungs and kidneys, invigorate the vital energy and asthma, and tonify the kidneys to absorb Qi. It is recommended to eat foods with the effects of invigorating lung Qi, consolidating kidney Qi, and nourishing essence.

　　3. It is recommended to eat sea pine nuts, jujube, peach, chestnut, peanut, silver ear, royal jelly, dangshen, taizishen, beef, milk, sesame, bird's nest, pork lung, etc. frequently.

　　1. Treatment

　　For patients with special etiology, etiological therapy should be performed, such as removing foreign bodies, applying antibiotics and antituberculosis treatment, etc. Generally, nebulized inhalation is used to absorb tracheal secretions, and the position of the child should be changed frequently, or the back patting method should be used to make the secretions easy to be excreted outward. Symptomatic treatment can use bronchodilators, anti-inflammatory drugs, and expectorant asthma drugs. Oxygen should be provided when there is difficulty breathing. If there is still infection in the atelectatic lung, antibacterial drugs should be used, generally starting with intramuscular penicillin, and changing to other antibacterial drugs if ineffective. If necessary, bronchial lavage and secretion aspiration should be performed.

　　2. Prognosis

　　Bronchiolitis, bronchopneumonia, asthma with atelectasis, mainly occur in the extreme stage of the disease. After the original disease is cured, atelectasis will disappear. In the case of pancreatic cystic fibrosis, due to the bronchus being filled with mucus-like substances, it is often necessary to use mucus solubilizers or bronchoscopy, mechanical sputum aspiration, and the lumen can be unobstructed. The younger the age of the child who inhales foreign objects, the more likely they are to develop atelectasis. The peanuts or beans inhaled can swell and increase in size, making them difficult to remove. X-ray films do not show shadows, making it easy to miss the diagnosis, and secondary infection may occur later. Atelectasis caused by whooping cough, adenovirus pneumonia, tuberculosis, and other diseases can lead to permanent fibrosis and bronchiectasis. The prognosis depends on the etiology of the atelectasis, the duration of atelectasis, whether there is a concurrent infection, the age of the child, whether the obstruction can be cleared in time, whether the large lung collapse causes pulmonary dysfunction and treatment is ineffective, whether the inhaled foreign body is not discovered and secondary infection occurs, cystic fibrosis, or severe congenital heart disease patients with atelectasis, the prognosis is poor.