What is Mendelson's Syndrome?
Mendelson's syndrome is a chemical pneumonitis caused by pulmonary aspiration of acidic gastric contents, resulting in acute lung injury without bacterial infection. 1
Pathophysiology
The syndrome was first described by Mendelson in 1946 in obstetric patients and represents acid aspiration syndrome rather than bacterial pneumonia 1. The condition develops through three distinct pathological phases 2:
- Initial injury phase: Direct chemical cauterization and necrosis of bronchial and alveolar epithelium, with complement activation 2, 3
- Exsudative phase: Development of alveolar edema, impaired surfactant synthesis, and formation of hyaline membranes rich in immunoglobulin M 2, 3
- Proliferative phase: Intraalveolar and interstitial fibrosis processes 2, 3
Both gastric hydrochloric acid and pepsin are causative agents, with gastric pH and volume determining severity of pneumonitis 1, 3.
Clinical Presentation
The classic triad consists of:
The condition manifests as acute respiratory distress syndrome (ARDS) with diffuse alveolar filling pattern on imaging 2, 5. Patients can deteriorate rapidly within hours, requiring mechanical ventilation 6, 7.
Key Clinical Distinctions
Mendelson's syndrome is sterile chemical pneumonitis, not bacterial aspiration pneumonia 6. However, it can be complicated by secondary bacterial infection 7. Bronchoscopy characteristically reveals burn lesions along the airway 6.
Incidence and Outcomes
The actual incidence of pulmonary aspiration is low (1 in 7,000), with morbidity at 1 in 1,700 and mortality at 1 in 100,000 1. Even in Mendelson's original series of 66 cases, no deaths occurred from pneumonitis itself—the only two deaths resulted from upper airway obstruction by solid food particles 1.
Prevention Context
The fear of Mendelson's syndrome historically drove excessive preoperative fasting practices, though prolonged fasting is now recognized as unnecessary and detrimental to patient well-being 1. Modern evidence supports clear fluids until 2 hours before surgery in adults without increasing aspiration risk 1.