Aspiration Syndromes

Aspiration of material that is foreign to the lower airway produces a varied clinical spectrum ranging from an asymptomatic condition to acute life-threatening events, such as occur with massive aspiration of gastric contents or hydrocarbon products. Other chapters discuss mechanical obstruction of large- or intermediate-size airways as occurs with foreign bodies (see Chapter 414 ) and infectious complications of aspiration and recurrent microaspiration (see Chapter 426 ), such as may occur with gastroesophageal reflux (see Chapter 349.1 ) or dysphagia (see Chapter 332 ). Occult aspiration of nasopharyngeal secretions into the lower respiratory tract is a normal event in healthy people, usually without apparent clinical significance.

Gastric Contents

Aspiration of substantial amounts of gastric contents typically occurs in the context of vomiting. It is an infrequent complication of general anesthesia, gastroenteritis, or altered level of consciousness. Among 63,180 pediatric patients undergoing general anesthesia, 24 cases of aspiration occurred, but symptoms developed in only 9. Pathophysiologic consequences can vary, depending primarily on the pH and volume of the aspirate and the amount of particulate material. Increased clinical severity is noted with volumes greater than approximately 0.8 mL/kg and/or pH < 2.5. Hypoxemia, hemorrhagic pneumonitis, atelectasis, intravascular fluid shifts, and pulmonary edema all occur rapidly after massive aspiration. These occur earlier, become more severe, and last longer with acid aspiration. Most clinical changes are present within minutes to 1-2 hr after the aspiration event. In the next 24-48 hr, there is a marked increase in lung parenchymal neutrophil infiltrations, mucosal sloughing, and alveolar consolidation that often correlates with increasing infiltrates on chest radiographs. These changes tend to occur significantly later and are more prolonged after aspiration of particulate material. Although infection usually does not have a role in initial lung injury after aspiration of gastric contents, aspiration may impair pulmonary defenses, predisposing the patient to secondary bacterial pneumonia. In the patient who has shown clinical improvement but then demonstrates clinical worsening, especially with fever and leukocytosis, secondary bacterial pneumonia should be suspected.

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