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.

The association between gastroesophageal reflux (GER) and the development of chronic respiratory symptoms or even aspiration pneumonia is not entirely understood. These disorders coexist, and the influence of this common gastrointestinal condition on respiratory function as well as the influence of respiratory conditions on GER, continues to be explored. Some literature suggests that reflux of gastric contents into the esophagus, as measured by pH probe, is associated with respiratory symptoms in children.⁵ Chronic microaspiration may explain some chronic respiratory symptoms.^6,7 Further, certain respiratory conditions, including asthma, may worsen the severity of GER.^7,8 Conversely, between 50% and 80% of children with chronic respiratory disease have some degree of GER. In addition to asthma, GER commonly accompanies cystic fibrosis and bronchopulmonary dysplasia.^7,9,10 Other chronic medical conditions that are associated with an increased risk of aspiration syndromes are also associated with GER (Table 142-2).⁷

Although there is clearly a relationship among GER, recurrent aspiration, and respiratory disease, the specific interactions have not been fully elucidated.^7,10 Nevertheless, acute and chronic respiratory disease related to aspiration accounts for much of the morbidity and mortality in children with impaired gastric motility and swallowing disorders as well as in children with anatomic abnormalities of the aerodigestive tract, including tracheoesophageal fistula.^3,7

ASPIRATION PNEUMONITIS

Mendelson first described the clinical manifestations of the aspiration of gastric contents into the lower respiratory tract in 1946 in a patient who developed pneumonitis after receiving general anesthesia for an obstetric procedure.¹¹ Any condition that depresses a child’s level of consciousness and impairs airway reflexes predisposes to aspiration. This risk factor includes exposure to alcohol, sedatives, paralytic agents, and other anesthetic agents.^12,13 Loss of airway protective reflexes may also occur in children with central nervous system disorders (see Table 142-2).^14,15 Infants and children with dysphagia and even respiratory distress are at increased risk of aspiration as well.

Aspiration pneumonitis may occur after a witnessed episode of vomiting in a patient at risk. In such instances, a sudden change in respiratory status is often noted. However, aspiration pneumonitis may also present in a subacute fashion. It may exacerbate a preexisting condition such as cerebral palsy, or it may complicate a concurrent condition such as tachypnea in an infant with bronchiolitis. Aspiration pneumonitis should also be considered when there is a change in the respiratory status of a patient who is predisposed to aspiration (Figure 142-1).¹⁰

Chemical injury to the lung may occur as a result of the inhalation of gastric acids, which are usually sterile due to their low pH.^6,9 However, children receiving acid-suppressing or acid-blocking therapy (e.g. antacids, proton pump inhibitors) as well as children fed through gastrostomy or nasogastric tubes, often have an elevated gastric pH with consequent bacterial colonization of the stomach.^9,16 Lung damage is related to the acidity of the aspirate, with a more pronounced inflammatory response occurring at lower levels of pH.⁶ Additionally, aspirates containing large amounts of particulate food matter increase the inflammatory response. With aspiration of acidic gastric contents, the fluid may be sterile, so bacterial infection is not a significant part of the early process.

Aspiration pneumonitis may also occur in children who have ingested mineral oil (Figure 142-2) or hydrocarbons, which can cause severe respiratory compromise. The inhalation may occur during the ingestion or during the regurgitation that often follows. The risk of aspiration and the severity of the lung injury are related to the viscosity (volatility) of the ingested hydrocarbon; higher-viscosity liquids (e.g. oils), which are less volatile, are less dangerous than lower-viscosity liquids (e.g. furniture polishes), which have greater volatility.

ASPIRATION PNEUMONIA

Aspiration pneumonia is an infectious process resulting from the inhalation of oropharyngeal secretions that are colonized by pathogenic bacteria. In contrast to aspiration pneumonitis, bacterial colonization and infection of the lower respiratory tract commonly occur. Children with dysphagia and impaired gastric motility as well as those with poor dental hygiene, are at risk for aspiration pneumonia, as are those with underlying neurologic and neuromuscular disorders.^5,7,17,18 GER may predispose to the development of aspiration pneumonia; however, in a neurologically normal child, intact airway defenses such as the gag and cough reflexes usually prevent this complication.^7,19 Enteral feeding through gastrostomy and nasogastric tubes also increases the likelihood of aspiration pneumonia.^16,20 Patients with aspiration pneumonia may have either an acute or a gradual onset of symptoms, and the aspiration event is often unwitnessed.