Acute and chronic laryngeal and tracheal stenosis - Causes and pathogenesis

Causes of acute and chronic stenosis of the larynx and trachea

Among the etiological factors are infectious-allergic, iatrogenic, neurogenic, traumatic, idiopathic, compression (compression of the laryngeal tracheal structures from the outside). The causes of acute laryngeal stenosis may be:

• acute inflammatory processes of the larynx or exacerbation of chronic ones (edematous, infiltrative, phlegmonous or abscessing laryngitis, exacerbation of chronic edematous-polyposis laryngitis);
• mechanical, thermal and chemical injuries to the larynx;
• congenital pathology of the larynx;
• foreign body of the larynx;
• acute infectious diseases (diphtheria, scarlet fever, measles, typhus, malaria, etc.):
• allergic reaction with the development of laryngeal edema;
• other diseases (tuberculosis, syphilis, systemic diseases).

The causes of chronic stenosis of the larynx and trachea can be:

• long-term artificial ventilation and tracheostomy;
• thyroid gland operations with damage to the recurrent nerves and the development of bilateral laryngeal paralysis as a result of disruption of its innervation (of peripheral and central origin);
• mechanical trauma to the larynx and chest;
• purulent-inflammatory diseases complicated by perichondritis of the larynx and trachea.

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Pathogenesis of acute and chronic stenosis of the larynx and trachea

The pathogenesis of acute and chronic cicatricial stenosis of the upper respiratory tract depends on the etiologic factor. Damage to the mucous membrane, especially in combination with trauma to the muscles and cartilages of the trachea, leads to infection of its wall and the development of a purulent-inflammatory process in it. At different stages of stenosis formation, the main factors determining pathological manifestations are considered to be the development of hypoxia (oxygen starvation) and hypercapnia (excess carbon dioxide in the blood). The accumulation of CO2 causes excitation of the respiratory and vasomotor centers. Against the background of acute hypoxia, symptoms of CNS damage develop: fear, motor agitation, tremor, impaired cardiac and vegetative activity. These changes are reversible with timely treatment. If the cause of stenosis is difficult to eliminate, then at the end of the acute period, from which the patient is removed using a tracheostomy, the disease takes a long chronic course.

The pathogenesis of chronic stenosis of the larynx and trachea depends on the intensity of the damaging factor, the time of its impact and the area of distribution. Paralytic stenosis of the larynx is caused by impaired mobility of its elements. The causes of these conditions may be laryngeal paralysis of various etiologies, ankylosis of the periarytenoid joints, leading to a median or paramedian position of the vocal folds.

Post-intubation changes in the larynx and trachea occur as a result of trauma during the insertion of the tube and its pressure on the mucous membrane of the larynx and trachea during artificial ventilation of the lungs, failure to comply with the technique of intubation, tracheostomy. Among other factors influencing the development of complications, the duration of intubation, the size, shape and material of the tube, its displacement in the lumen of the larynx are noted. The following mechanism of development of the cicatricial process is described: the damaging factor causes the formation of a defect in the mucous membrane and cartilages of the larynx and trachea, a secondary infection joins in, which provokes chronic inflammation spreading to the mucous membrane, perichondrium and cartilaginous skeleton of the upper respiratory tract. This leads to the formation of coarse cicatricial tissue and cicatricial deformation of the lumen of the larynx and trachea. The process is extended in time and lasts from several weeks to 3-4 months. Inflammation of the cartilaginous tissue is an obligatory component in the development of chronic stenosis.

The pathogenesis of post-intubation cicatricial stenosis of the larynx and trachea is based on ischemia of the mucous membrane of the larynx and trachea in the pressure zone of the intubation tube.

The reasons for the development of the cicatricial-stenotic process may be:

• trauma to the mucous membrane of the larynx and trachea during intubation;
• pressure of the inflatable cuff on the mucous membrane of the respiratory tract;
• shape and size of the intubation tube:
• the material it is made of;
• composition of the microflora of the lower respiratory tract (including bacterial inflammation):
• tracheostomy with damage to the cricoid cartilage, Bjerck tracheostomy:
• atypical lower tracheostomy;
• bacterial inflammation of the tracheostomy area;
• duration of intubation.
• medial surface of the arytenoid cartilage, cricoarytenoid joint, vocal processes:
• posterior part of the glottis and interarytenoid region;
• the inner surface of the cricoid cartilage in the subchondral region;
• tracheostomy area:
• place of fixation of the inflatable cuff in the cervical or thoracic part of the trachea:
• level of the distal part of the endotracheal tube.

Impaired mucociliary clearance leads to secretory stasis and promotes infection, leading to perichondritis, chondritis, and then to necrosis spreading to the cricoid cartilage, cricoarytenoid joint, and cartilaginous structures of the upper trachea. Three periods can be clearly traced in the dynamics of the wound process:

• melting of necrotic tissue and cleansing of the defect through inflammation;
• proliferation of connective tissue elements with the formation of granulation tissue that repairs the damage:
• fibrosis of granulation tissue with scar formation and epithelialization of the latter.

The general condition of the patient, concomitant diseases, traumatic brain injuries, diabetes mellitus, and the patient’s age are of great importance in the pathogenesis of stenosis.

Stenosis of the upper respiratory tract, both acute and chronic, leads to the development of respiratory failure of the obstructive type of varying severity. In this case, the normal gas composition of the blood is not maintained, or is ensured by the inclusion of compensatory mechanisms, which leads to a decrease in the functional capabilities of the body. With prolonged hypoxia, the body adapts to new conditions through organ restructuring (changes in the lungs, cerebral circulation and intracranial pressure, expansion of the heart cavities, disruption of the blood coagulation system, etc.). These changes can be called stenotic disease.

As a result of the cicatricial process against the background of chronic inflammation, structural and functional damage to the larynx and trachea of varying degrees of severity develops, which leads to persistent disability of patients.