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Mendelsohn syndrome
Last reviewed: 04.07.2025
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Mendelson's syndrome is aspiration of a chemically aggressive substrate with subsequent burn and development of hyperergic reaction of the respiratory tract. Development of chemical burn of the respiratory tract mucosa can be caused by the effect of acidic, enzyme-rich gastric juice.
[ What causes Mendelson syndrome?
Mendelson's syndrome can develop when even a small amount of gastric juice with a low pH (20-30 ml or less) enters the respiratory tract. The worst prognosis is observed in cases of aspiration of a large volume (> 0.4 ml/kg) of acidic contents (with a pH < 2.5). Damage to the epithelium of the trachea, bronchi, bronchioles, alveolar walls and the endothelium of pulmonary capillaries can also occur at higher pH values (> 5.9), especially if there is a parallel ingestion of bile, gastric enzymes and other biologically active substrates.
Mendelson's syndrome can develop when mineral oils, fats and other lipophilic substances enter the respiratory tract, which leads to the development of non-infectious inflammation in the lungs - "fatty pneumonia".
This term refers to alveolar infiltration that occurs when oils or fatty substances are aspirated. It may occur when oil-based oral or nasal agents are used to soften the mucous membranes of the upper respiratory tract.
The severity of the lesion is directly dependent on the acidity of the amount of aspirated gastric juice.
An acid burn leads to the development of a hyperergic reaction of the respiratory tract epithelium, increased permeability of the alveolocapillary membranes, the release of the plasma portion of the blood into the pulmonary interstitium and alveolar cavities, the development of interstitial edema and acute lung injury. There is a pronounced edema of the mucous and submucous layers of the bronchi, bronchiolospasm, bronchial obstruction, damage to the surfactant system, atelectasis of part of the lung, decreased pulmonary perfusion, opening of intrapulmonary arteriovenous shunts and direct damage to the alveoli.
The local effect of the chemically active substrate on the lung parenchyma plays an important role.
There is a release of biologically active substances, the complement systems are activated, the tumor necrosis factor, various cytokines and substances that determine leukocyte chemotaxis are released. Systemic damage to the endothelium occurs. Reflex development of laryngo- and bronchiolospasm aggravates the severity of the patient's condition and can be accompanied by severe cardiac disorders.
What are the symptoms of Mendelson syndrome?
Mendelson syndrome is characterized by an acute onset (usually immediately after aspiration).
It is the development of hypoxemia in the first 10 minutes after aspiration that serves as the most important sign.
As a rule, the patient experiences increasing anxiety, signs of respiratory distress (laryngospasm, bronchospasm, expiratory dyspnea similar to an asthmatic condition).
Mendelson syndrome is characterized by a triad of symptoms:
- tachycardia;
- tachypnea;
- cyanosis.
Reflex disorders of the cardiovascular system are observed (primarily a drop in blood pressure). At the moment of aspiration of acidic gastric contents, bronchiolospasm occurs.
Against the background of urgent medical measures, a temporary improvement in the condition occurs - a clear interval (can last several hours). But later, signs of obstructive (bronchiolitis) and restrictive (pneumonitis) disorders appear.
Cyanosis and low Sp O2 values do not decrease even with 100% oxygen administration (hypoventilation with maintained blood flow leads to venous blood shunting).
How to recognize Mendelson syndrome?
When auscultating the lungs, wheezing sounds are heard in all fields (crepitating wheezing may be heard in the lower sections). Wheezing on exhalation indicates obstruction of small-caliber bronchi.
As respiratory disorders progress, a decrease in PaO2 to 35-45 mm Hg, an increase in pulmonary vascular resistance and pulmonary artery pressure are observed. Lung compliance decreases, aerodynamic resistance of the respiratory tract increases, and acute lung injury develops.
X-ray examination reveals areas of decreased airiness and diffuse darkening of the lung tissue (the picture of "shock lung"). Often there is a diffuse spotty darkening with predominant damage, usually to the right lung, since gastric contents more often get there.
In mild cases, the process resolves in the next few days (sometimes even without special treatment). But after apparent improvement in some patients, after 2-5 days, signs of respiratory failure reappear. fever, cough, leukocytosis. That is, symptoms of secondary bacterial pneumonia with radiographic foci of infiltration appear.
Since pneumonitis can be caused by aspiration of various biologically aggressive fluids, Mendelson's syndrome (a chemical burn caused by the action of gastric juice) and aspiration pneumonitis (caused by any chemically aggressive substance) should not be considered synonymous. Figuratively speaking, any Mendelson's syndrome is essentially an aspiration pneumonitis, but not every aspiration pneumonitis can be called this disease.