The term aspiration encompasses a variety of respiratory syndromes, and many medical conditions can predispose to aspiration. Foreign body inhalation and the aspiration of infectious or noninfectious oropharyngeal secretions and gastric contents are scenarios that may lead to the development of pulmonary symptoms. An accurate and timely diagnosis of an acute or chronic aspiration syndrome requires a careful history and physical examination, because highly sensitive and specific diagnostic tests are lacking.
When aspiration leads to acute injury to the airways and lung parenchyma, two specific types of aspiration syndrome can be identified: aspiration pneumonitis and aspiration pneumonia. These aspiration syndromes are distinct entities, but considerable overlap exists. Attempts to distinguish between them may be important, because the appropriate evaluation, management, treatment, and prevention strategies differ.
Aspiration pneumonitis occurs after gastric contents, which are typically acidic, are inhaled into the lower respiratory tract. A prompt and intense inflammatory reaction, or pneumonitis, ensues, but bacterial infection is not a significant part of this immediate reaction. Aspiration pneumonia occurs after inhalation of nasal or oropharyngeal secretions, which contain colonizing bacteria, into the lower airways. The infectious process that develops accounts for the clinical features of aspiration pneumonia. The key to either diagnosis is identifying those patients at risk for aspiration.
Even healthy adults and children may aspirate small amounts of oropharyngeal contents during sleep; however, pulmonary host defense mechanisms usually prevent the development of infection and mitigate the inflammatory response.1 There is a relatively low burden of virulent organisms colonizing the mouth and the naso- and oropharynx in healthy children; thus, aspiration of small amounts of normal flora rarely culminates in a clinically significant pulmonary infection.2 Additionally, there are protective mechanisms at all levels of the respiratory system; these include the anatomic design of the airway, functional gag and cough reflexes, the mucociliary clearance system, and the innate antibacterial and anti-inflammatory properties of surfactant and airway surface liquid (Table 142-1).3,4 Impairment of any of these protective barriers places a child at risk for the development of an aspiration syndrome.
TABLE 142-1Major Airway Defenses ||Download (.pdf) TABLE 142-1 Major Airway Defenses
|Type of Defense ||Mechanism |
|Upper airways ||Mechanical trapping of bacteria in nasal passages and larynx, and frequent branching of upper bronchial tree |
|Mucociliary transport ||Prevents most particulate matter in inspired air from reaching lung parenchyma |
|Cough reflex ||Aspiration of large amounts of oropharyngeal material, including flora of the upper respiratory tract, may be prevented by cough and laryngeal reflexes |
|Local immunoglobulin ||Immunoglobulin (primarily IgA), complement, and glycoproteins such as fibronectin in airway secretions prevent colonization of the oropharynx by virulent organisms such as Streptococcus pneumoniae, Pseudomonas aeruginosa, and Klebsiella pneumoniae, which can readily cause lower respiratory tract infection after scant aspiration of oropharyngeal contents |
|Humoral and cellular defenses of ...|