A 60-year-old man comes to the emergency department due to several hours of right lower quadrant pain and vomiting. His oral intake has been minimal for the last 12 hours. Past medical history is notable for well-controlled hypertension. An abdominal CT scan demonstrates appendicitis, and the patient is taken to the operating room. He vomits during rapid sequence induction for intubation, requiring repeat suctioning from the mouth and trachea. The surgery is otherwise uneventful; the patient receives a total of 2 liters of intravenous crystalloids in the intra- and peri-operative period and maintains normal hemodynamics and urine output. Approximately 4 hours later, he is tachypneic and hypoxemic. Temperature is 37.2 C (99 F), blood pressure is 150/80 mm Hg, and pulse is 95/min and regular. Pulmonary examination reveals bilateral crackles. ECG is unremarkable. Arterial blood gas analysis demonstrates PO₂ of 67 mm Hg on a fraction of inspired oxygen of 90%. Chest x-ray reveals bilateral infiltrates. Which of the following is the most likely mechanism of lung injury?

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11ec25c8_d939_7143_bc81_8ddc6c586f5a_MD0003_00 This patient had a witnessed aspiration event (vomiting during intubation that required suctioning) a few hours ago and now has profound hypoxemia with bilateral infiltrates on chest x-ray. He likely has aspiration pneumonitis, an acute lung injury due to aspiration of acidic and sterile stomach contents. The gastric acid induces a chemical burn and consequent inflammatory response, usually within hours of the aspiration event. Bilateral infiltrates can sometimes be seen on chest imaging. The symptoms (and infiltrates) usually resolve rapidly (24-48 hours) with supportive management. By contrast, aspiration pneumonia (Choice B), which usually occurs in individuals with impaired level of consciousness (eg, following overdose, seizure, or anesthetic use), is caused by inhalation of pathogenic bacteria that colonize oropharyngeal secretions. A typical presentation would be that of an institutionalized elderly patient who has dysphagia and develops fever and cough days (not hours) following an (often unwitnessed) aspiration event. Treatment requires antibiotics. (Choice A) Cardiogenic pulmonary edema is less likely as this patient has no history of congestive heart failure, only received 2 liters of fluids, has had normal urine output, has a normal ECG, and had a witnessed aspiration episode. Acute respiratory distress syndrome, which can occur following both aspiration pneumonitis or aspiration pneumonia and is characterized by profound hypoxemia and diffuse bilateral pulmonary infiltrates, would cause noncardiogenic rather than cardiogenic edema. (Choice D) Negative pressure pulmonary edema occurs when a patient has upper airway obstruction (eg, laryngospasm during extubation) that results in large negative intrathoracic pressure (due to inspiration against the obstruction), causing noncardiogenic pulmonary edema. It is more common in young men or after head and neck surgery. (Choice E) Ventilator-associated pneumonia is a lung infection that typically develops after 2 days of intubation and frequently presents with fever. Educational objective: Aspiration pneumonitis is an acute lung injury secondary to a chemical burn from aspirated sterile gastric contents. In contrast, aspiration pneumonia is an infectious disease caused by aspiration of infected oropharyngeal secretions. References: Healthcare-associated Pneumonia and Aspiration Pneumonia. (http://www.ncbi.nlm.nih.gov/pubmed/25657850) Aspiration-induced lung injury. (http://www.ncbi.nlm.nih.gov/pubmed/21263315)

A 60-Year-Old Man Comes to the Emergency Department Due to Several