Mendelson syndrome is an acute aspiration pneumonitis that develops as a result of acidic gastric contents entering the respiratory tract. It occurs more often as a complication of an anesthetic aid. The Mendelson syndrome clinic unfolds in a matter of hours and includes shortness of breath, fever, respiratory failure, and bacterial pneumonia. The syndrome is diagnosed on the basis of clinical, auscultative and radiological data. First aid involves aspiration of the contents from the respiratory tract, elimination of bronchospasm, transfer of the patient to a ventilator, conducting a therapeutic bronchoscopy. In the future, decongestant and antibacterial therapy is prescribed.
J95.4 Mendelson syndrome
Mendelson syndrome (aspiration pneumonitis, acid aspiration syndrome) is an acute lung injury of a non-infectious nature associated with the ingress of acidic stomach contents into the lower respiratory tract. For the first time this condition was described in 1946 by S.L. Mendelson as the most severe complication of obstetric anesthesiology, characterized by high mortality (more than 50-60%). However, due to the widespread use of general anesthesia, this iatrogenic complication may occur in other categories of surgical patients. To date, the issues of prevention and treatment of Mendelson syndrome are still relevant for clinical pulmonology, obstetrics, anesthesiology and intensive care.
Mendelson syndrome causes
The only possible cause of Mendelson syndrome is aspiration of stomach contents, the damaging effect of which is associated with high acidity of the chyme. An aggressive substrate leads to severe chemical burns and swelling of the mucous membrane of the respiratory tract, rapid destruction of the epithelium of the bronchioles and alveoli and perspiration of the transudate into the alveoli. This is accompanied by the development of non-cardiogenic pulmonary edema and respiratory distress syndrome (hypoxemic form of respiratory failure).
In some cases, together with gastric juice, undigested food particles may enter the respiratory tract, causing mechanical blockage of the bronchi of medium caliber (asphyxiated form of respiratory failure). In both cases, bronchial obstruction eventually develops.
For the appearance of the clinic of Mendelson syndrome, it is enough to get even a small volume (20-30 ml) of gastric juice with a low pH into the respiratory tract. The most severe damage is noted when a large amount of acidic contents (>0.4 ml/kg) with a pH of 5 is aspirated.
Factors predisposing to aspiration or regurgitation of stomach contents and the development of Mendelson syndrome are disorders of consciousness caused by general anesthesia, alcohol or narcotic intoxication, the effect of sedatives, TBI, coma. Most often, Mendelson syndrome occurs as a complication of emergency surgical interventions (more often abdominal operations and cesarean section), when due attention is not paid to the preparation of the gastrointestinal tract. Additional risk factors are increased intra-abdominal pressure (in pregnant women in the third trimester, obese patients, with intestinal paresis), gastrointestinal diseases (gastric ulcer and duodenal ulcer, esophagitis, gastritis, esophageal dilation, esophageal diverticulum, hernia of the esophageal orifice of the diaphragm).
Symptoms of Mendelson syndrome
The Mendelson syndrome clinic unfolds very quickly, within a few hours. Pathological changes go through three phases: acute laryngospasm and bronchiolospasm, partial relief of bronchiolospasm and an increase in acute respiratory failure.
In the first minutes after aspiration, as a result of reflex narrowing of the bronchioles, cough, expiratory dyspnea, cyanosis of the skin, tachycardia, decreased blood pressure occurs. The first phase of Mendelson syndrome is often mistaken for an attack of bronchial asthma. Various moist and whistling wheezes are heard in the lungs; there is an increase in the central nervous system, swelling of the neck veins. One of the I—III art. develops rapidly; already at the first stage, a fatal outcome from asphyxia is possible.
The second phase is marked by spontaneous partial expansion of the bronchioles and some clinical improvement. The patient’s condition temporarily stabilizes: shortness of breath decreases, pressure decreases. After about 48 hours, the third phase of Mendelson syndrome begins. During this period, the phenomena of bronchiolitis and pneumonitis rapidly increase, which causes a new deterioration of the patient’s condition and the progression of respiratory failure. Bacterial complications are added – aspiration pneumonia develops (fever, cough with sputum, leukocytosis). The fatal outcome usually comes from pulmonary edema.
For the clinical diagnosis of Mendelson syndrome, a characteristic triad of symptoms (tachypnea, tachycardia, cyanosis) is important, as well as the inability to eliminate hypoxemia even with the supply of pure oxygen (this sign indicates venous blood bypass). When monitoring the blood gas composition, there is a decrease in RaO2 to 35-45 mm Hg. The auscultative picture is characterized by the presence of multiple whistling wheezes (in the lower parts – creeping wheezes).
During bronchoscopy, edema and hyperemia of the mucous membrane are detected, the presence of aspirated fluid in the lumen of the bronchi, often with lumps of food. Lung x-ray show foci of hypoventilation, diffuse darkening of the pulmonary fields (“shock lung”). With the addition of secondary bacterial pneumonia, foci of infiltration appear.
Mendelson syndrome treatment
Emergency care should be provided to the patient immediately after establishing the fact of aspiration of gastric contents. First of all, it is necessary to immediately remove the aspirate from the oral cavity and respiratory tract using an electric pump. After that, the trachea is intubated and the patient is transferred to a ventilator in hyperventilation mode with 100% oxygen inhalation. In the future, probe emptying of the stomach and sanitization bronchoscopy are performed: sterile saline is used for bronchoalveolar lavage. Treatment of a patient with Mendelson syndrome is carried out in the ICU jointly by anesthesiologists, resuscitators and pulmonologists.
In order to eliminate bronchiolospasm, atropine, euphyllin, prednisone or dexamethasone, orciprenaline are administered. Percussion chest massage is required. To neutralize high acidity, alkaline inhalations of sodium bicarbonate solution are carried out. Infusion of electrolyte solutions, glucose, freshly frozen plasma, albumin; stimulation of diuresis is carried out. Antibiotic therapy is indicated for the prevention and treatment of aspiration pneumonia. Extubation is performed after restoration of spontaneous respiration and independent ability to maintain adequate gas exchange.
Prognosis and prevention
Deaths in the occurrence of Mendelson syndrome are observed in 60% of cases, and in obstetric practice – in more than 70% of cases. To prevent this terrible complication, before emergency operations, it is necessary to evacuate the gastric contents with a probe (except in cases where this is contraindicated – for example, with gastric bleeding). Before planned operations, it is forbidden to take food and liquids 10-12 hours before the intervention, if necessary, antacids, H2 blockers and prokinetics are prescribed. In order to avoid Mendelson syndrome, it is necessary to observe the correct algorithm of the anesthetic manual during emergency surgical interventions.
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- Bynum LJ, Pierce AK. Pulmonary aspiration of gastric contents. Am Rev Respir Dis. 1976 Dec;114(6):1129-36. – link
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