Aspiration Pneumonia and Lung Abscess



Aspiration pneumonia may be due to inhalation of gastric juice or oropharyngeal contents, foreign body aspiration, and the spontaneous intrabron-chial drainage of purulent material from a dis­eased lung to the contralateral healthy lung. Im­pairment of the airway’s protective mechanisms, especially cough and glottic closure, is the major predisposing factor and is most often seen in pa­tients with neurological disorders or acute loss of consciousness, especially in the presence of poor dentition. Pulmonary injury includes chemical pneumonitis, necrotizing pneumonia, lung ab­scess, and empyema. Anaerobic bacteria are the major pathogens in community-acquired aspira­tion pneumonia, while aerobic organisms such as S. aureus, S. pyogenes, and various GNB are less commonly responsible but predominate in hos­pitalized patients. Onset of disease is insidious, beginning as an acute pneumonic process with the development of an abscess or empyema after one to two weeks. Dependent areas of the lung are par­ticularly involved. The sputum and discharges are usually putrid and foul-smelling, but this is not invariable. Diagnosis of bacterial etiology should not be based on sputum examination because of the frequency of contamination by upper airway organisms. If a specific bacteriological diagnosis is desired, invasive techniques such as transtra­cheal aspiration, transthoracic aspiration, or bron­choscopy are required. Since S. aureus and GNB are so easily recovered from mixed culture sam­ples, their absence in a purulent specimen usually excludes their presence in the lower respiratory tract. The converse cannot be said, however, and their growth should not be taken as an indication of their involvement. Treatment is usually em­pirical and consists of penicillin G, which is ef­fective even against organisms such as B. /ragilis that display in vitro resistance. Clindamycin is a reasonable alternative agent. Surgical resection of the abscess cavity or decortication of the pleural peel is rarely required.