Licensed books on medicine
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Parts of the respiratory tract are the nasopharynx, larynx, trachea and bronchial tree. The vast surface of the nasal cavity (nasal concha and septum), which is covered by a well-circulated mucosa, plays a large role in warming and moistening the inhaled air. Cilia of the epithelium are responsible for the capture and movement of small foreign particles. In children, the nasal passages and the lower respiratory tract (larynx, trachea, bronchial system) are narrow. Infants are also characterized by: a short neck, a large tongue, a long U-shaped epiglottis, which can complicate the visualization of the larynx during laryngoscopy. In newborns, the head is relatively large, so intubation is easier to perform when the neck is neutral. Enlarged adenoids or tonsils can also interfere with breathing. For mammals, nasal breathing is physiological, so in newborns it is important, as far as possible, to keep the nasal passages free.
The larynx can block the lower respiratory tract (for example, when swallowing, coughing). In adults, the narrowest part of the airways is the level of the vocal cords, where any additional narrowing creates difficulties for ventilation. The laryngeal mucosa may swell due to an anaphylactic reaction or trauma during intubation, creating life-threatening respiratory problems. In children, the larynx is located at the level of Sh-IV cervical vertebrae, i.e. one vertebra higher than in adults. The bottleneck up to the age of 8-10 years is not the vocal cord zone, but the cricoid cartilage. Anatomical narrowing contributes to the fact that inflammatory swelling of the mucosa caused by various causes (epiglottitis, laryngotracheobronchitis) can lead to an inspiratory stridor with life-threatening respiratory restriction.
The length of the trachea in adults is 10-12 cm and its diameter is 11-12.5 mm. It consists of 16-20 horseshoe-shaped cartilage rings connected by a connective tissue and smooth muscle (tracheal muscle) membrane. Trachea in newborns is only 4 cm long, in 2-year-old children it is 5 cm, and in 6-year-olds it is about 6 cm in length. The diameter of the trachea of the newborn is about 6 mm, in older children - about 11 mm. In addition, the main bronchi depart from the trachea at the same angle, so both right-side and left-side endobronchial intubation can easily be performed.
The division of the bronchial tree occurs at 23 levels (orders), from the 23rd alveoli begin. The total diameter of the airways increases significantly as you move to the periphery. Bronchioles start at 10th order. Their diameter is less than 1 mm. The wall does not contain cartilage and is rich in smooth muscle fibers. The epithelium no longer contains mucus-forming cells. Above 16 orders of magnitude, bronchioles play no role in gas exchange. Their sole purpose is to transport air.
Gas transportation zone = anatomical - zone
(dead space) gas exchange space
The gas exchange zone begins with respiratory bronchioles. Smooth muscle fibers are rare here, their clusters are found in the places where the alveoli discharge. Although the bronchial system in newborns and infants is relatively wider than in adults, but in fact, in absolute terms, it is narrow. This anatomical feature causes increased airway resistance. Swelling of the mucosa or bronchospasm (for example, with asthma, bronchiolitis) leads to a further increase in airway resistance with a sharp increase in the work of breathing. Therefore, obstructive ventilatory disorders in newborns and infants can be very difficult.
Mucociliary clearance is the most important cleansing mechanism of the peripheral part of the respiratory tract. The mucous membrane of the bronchial system contains the ciliary and glandular epithelium. The mucous layer covering the cilia consists of two layers: a liquid aqueous layer (sol) surrounding the cilia (periciliary liquid layer) and a surface colloidal layer (gel), to which foreign particles and microorganisms adhere. A liquid layer (sol) is necessary for the cilia to move freely. The movements of the cilia are directed to the mouth, which makes it possible to remove foreign particles and microorganisms.
Violations in the form of viscous-mechanical dissociation occur if:
• the periciliary layer is too deep (pulmonary edema, mucolytic overdose);
• the periciliary liquid layer is too thin (dehydration, insufficient gas humidification during mechanical ventilation);
• the composition of the mucus is pathologically altered (too viscous mucus due to insufficient water content - dyskrinia, with cystic fibrosis).
When the humidity of the airways is insufficient, the transport function of the respiratory cilia quickly ceases. Toxic gases and tobacco smoke also have a suppressive effect. Mucociliary clearance is reduced by anesthetics (thiopental), b-blockers, Pseudomonas aeruginosa due to the additional ciliostatic effect. Mucociliary clearance is enhanced by b-adrenergic agents, sympathetic stimulation and theophylline. Mucociliary transport is most significantly enhanced by cough (cough clearance). After the maximum increase in pressure, with the glottis closed, its sudden opening leads to the fact that a huge air flow in the wide airways makes it possible to remove large masses of mucus.
At the age of two years, the child has approximately 300 million alveoli, their total internal surface is about 80 m2. Alveoli are composed of alveolar epithelium, epithelial basement membrane and capillary endothelium. All these layers are called the alveolocapillary membrane. It has a thickness of about 1 μm - this is the diffusion distance during gas exchange between the alveolar space and the lumen of the capillary. The alveolar epithelium begins in the alveolar passages and consists of flat epithelial cells (the first type of cells) and alveolar granulocytes (the second type of cells), which produce a surfactant and have a rounded shape. Foreign particles that reach the alveolar space are removed due to alveolar macrophagocytosis. Surfactant is a phospholipid that reduces surface tension at the border of lung tissue and air, preventing alveoli from falling off at the end of exhalation.
The compliance (compliance, extensibility) of the lungs of newborns and infants is low and slowly increases with age. Spontaneous breathing in newborns, infants, and children occurs with increased airway resistance and low lung compliance. The endotracheal tube increases airway resistance, which causes spontaneously breathing children to increase their respiratory efforts. Therefore, it is advisable for intubated children to carry out at least auxiliary ventilation. The ribs of newborns and infants are located horizontally, the intercostal muscles are not developed as well as in older children and adults. The main respiratory muscle is the diaphragm. Obstruction to diaphragmatic breathing, caused, for example, by ileus or a tumor in the abdominal cavity, quickly leads to exhaustion of the main respiratory muscle due to an increase in respiratory effort. Moreover, the chest in infants is very elastic and when forced to breathe, it easily bends, thereby reducing the effectiveness of the movements of the diaphragm. Therefore, paradoxical respiratory movements (swaying breathing) together with insufficient ventilation in children occur relatively quickly. Important indicators of the physiology of respiration of newborns, infants, children and adults are given in table. 1.1.
| Table 1.1. Physiological indicators of respiration |
| Age || Respiratory rate (in 1 min) || Tidal Volume (ml / kg) || Resistance (see water. Art. X x l / s) || Compliance (ml / cm water) |
| Newborns || 40-60 || eight || 40 || 3-5 |
| Babies || 30-60 || eight || 20-30 || 10-20 |
| Children || 25-40 || eight || 20 || 20-40 |
| Adults || 12-20 || eight || 1-2 || 70-100 |
Breathing is the gas exchange between the body and its environment. External respiration includes ventilation and gas exchange. Biological oxidation, “burning” of nutrients with oxygen to carbon dioxide and water, is called internal respiration. In general, a healthy adult's body, consuming approximately 300 ml / min. 02 simultaneously produces about 250 ml / min. CO2. Consumption 02 = 3 - 5 ml / kg / min, production CO2 = 3 ml / kg / min.
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