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Aspiration is defined as the inhalation of either oropharyngeal or gastric contents into the lower airways, that is, the act of taking foreign material into the lungs. This can cause a number of syndromes determined by the quantity and nature of the aspirated material, the frequency of aspiration, a...

Aspiration is defined as the inhalation of either oropharyngeal or gastric contents into the lower airways, that is, the act of taking foreign material into the lungs. This can cause a number of syndromes determined by the quantity and nature of the aspirated material, the frequency of aspiration, and the host factors that predispose the patient to aspiration and modify the response. There are four types of aspiration syndromes. Aspiration of gastric acid causes a chemical pneumonitis which has also been called Mendelson syndrome. Aspiration of bacteria from oral and pharyngeal areas causes aspiration pneumonia. Aspiration of oil (eg, mineral oil or vegetable oil) causes exogenous lipoid pneumonia, an unusual form of pneumonia. Aspiration of a foreign body may cause an acute respiratory emergency and, in some cases, may predispose the patient to bacterial pneumonia. The pathophysiology, clinical presentation, treatment, and complications of each of these entities are different. This article concentrates on chemical pneumonitis and aspiration pneumonia. Aspiration pneumonia is caused by bacteria that normally reside in the oral and nasal pharynx. Historically, aspiration pneumonia referred to an infection caused by less virulent bacteria, primarily oral pharyngeal anaerobes, after a large volume aspiration event. It is now recognized that many common community-acquired and hospital- acquired pneumonias result from small-volume aspiration of more virulent pathogens from the oral cavity or nasopharynx, such as Streptococcus pneumoniae,Haemophilus influenza, Staphylococcus aureus, and gram-negative bacteria. Pathophysiology of Aspiration Pneumonia In aspiration pneumonia, an infiltrate develops in a patient at increased risk of oropharyngeal aspiration. This occurs when a patient inhales material from the oropharynx that is colonized by upper airway flora. The risk of aspiration is indirectly related to the level of consciousness of the patient (ie, decreasing Glasgow Coma Scale [GCS; see the Glasgow Coma Scale calculator] score is related with increased risk of aspiration). Aspiration of small amounts of material from the buccal cavity, particularly during sleep, is not an uncommon event. No disease ensues in healthy persons, because the aspirated material is cleared by mucociliary action and alveolar macrophages. The nature of the aspirated material, volume of the aspirated material, and state of the host defenses are three important determinants of the extent and severity of aspiration pneumonia. Chemical pneumonitis Chemical pneumonitis, also known as aspiration pneumonitis and Mendelson syndrome, is due to the parenchymal inflammatory reaction caused by a large volume of gastric contents independent of infection. In fact, aspiration of a massive amount of gastric contents can produce acute respiratory distress within one hour. This disease occurs in people with altered levels of consciousness resulting from seizures, cerebrovascular accident (CVA), central nervous system (CNS) mass lesions, drug intoxication or overdose, and head trauma. The acidity of gastric contents results in chemical burns to the tracheobronchial tree involved in the aspiration. If the pH of the aspirated fluid is less than 2.5 and the volume of aspirate is greater than 0.3 mL/kg of body weight (20-25 mL in adults), it has a greater potential for causing chemical pneumonitis. The initial chemical burn is followed by an inflammatory cellular reaction fueled by the release of potent cytokines, particularly tumor necrosis factor (TNF)–alpha and interleukin (IL)–8. Aspiration pneumonia Aspiration pneumonia most commonly occurs in individuals with chronically impaired airway defense mechanisms, such as gag reflex, coughing, ciliary movement, and immune mechanisms, all of which aid in removing infectious material from the lower airways. Aspiration pneumonia can occur in the community or in a hospital or health care facility (ie, nosocomial). In both situations, anaerobic organisms alone or in combination with aerobic and/or microaerophilic organisms play a role in the infection. In anaerobic pneumonia, the pathogenesis is related to the large volume of aspirated anaerobes (eg, as in persons with poor dentition, poor oral care, and periodontal disease) and to host factors (eg, as in alcoholism) that suppress cough, mucociliary clearance, and phagocytic efficiency, both of which increase the bacterial burden of oropharyngeal secretions. Nosocomial bacterial pneumonia caused by aspiration is common, and the major pathogens involved are hospital-acquired florae through oropharyngeal colonization (eg, enteric gram-negative bacteria, staphylococci). Selection and colonization of gram-negative organisms in the oropharynx, sedation, and intubation of the patient's airways are important pathogenetic factors in nosocomial pneumonia. Because of the relative sterility of normal gastric contents, bacteria do not play an important role in the early stages of the disease. This does not hold true in patients with gastroparesis or small-bowel obstruction or in those using antacids (proton pump inhibitors [PPIs], histamine 2-receptor antagonists). Regardless of the bacterial load of the inoculum, bacterial superinfection may occur after the initial chemical injury. Causative microorganisms Initial bacteriologic studies into the causative organisms revealed the anaerobic species to be the predominant pathogens in community-acquired aspiration pneumonia. However, subsequent studies revealed that Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Enterobacteriaceae are the most common organisms. In fact, in two studies of patients with acute, witnessed aspiration with protective specimen brush sampling and anaerobic culturing, no anaerobes were isolated. [8, 9] Moreover, hospital-acquired aspiration pneumonia is often caused by gram-negative organisms including Pseudomonas aeruginosa, particularly in intubated patients. While previous studies have suggested multidrug-resistant organisms, such as methicillin-resistant S aureus (MRSA), were more commonly found in those with healthcare-associated pneumonia (HCAP) versus community-acquired aspiration pneumonia (CAP), a 2014 meta-analysis of 24 studies found that patients previously classified as having HCAP (including nursing home– associated pneumonia) are not more likely to have multidrug-resistant infections than patients classified as having CAP. [11, 12] These studies demonstrated a limited role of anaerobic pathogens in both the community and nosocomial variants of the disease. Epidemiology of Aspiration Pneumonia A reliable estimate of incidence of chemical pneumonitis is not available. Few studies have been designed that distinguish between aspiration pneumonia and aspiration pneumonitis. Several studies suggest that 5-15% of the 4.5 million cases of community-acquired pneumonia (CAP) result from aspiration pneumonia. A retrospective review found that the 30-day mortality rate from aspiration pneumonia is 21% overall and slightly higher in healthcare- associated aspiration pneumonia (29.7%). Nosocomial bacterial pneumonia is the second most likely cause of nosocomial infections, second only to urinary tract infection, and it is the leading cause of death from hospital-acquired infections. Approximately 10% of patients who are hospitalized after drug overdoses will have an aspiration pneumonitis. Nosocomial bacterial pneumonia caused by aspiration is much more frequent in adults than in children, and males are more commonly affected than females. Predisposing factors (see Predisposing Conditions for Aspiration Pneumonia) are more common among elderly people. Thus, this population is more prone to develop aspiration pneumonia. Comparative studies of bacterial pneumonia in patients from the community with those in a continuing care facility have demonstrated a 3-fold increase of this disease in residents of the continuing care facilities (the majority of them had neurologic disease with dysphagia). Presentation of Aspiration Pneumonia The clinical presentation of both aspiration pneumonia and pneumonitis ranges from mildly ill and ambulating to critically ill, with signs and symptoms of septic shock and/or respiratory failure. Host factors and chronic conditions that result in a decreased ability to protect one's airway include a previous cerebrovascular accident (CVA), a history of esophageal diseases including achalasia or esophageal web, being a nursing home patient, and being chronically fed by feeding tube (nasogastric [NG] tube or gastric tube). Physical examination findings vary depending on the severity of the disease, presence of complications, and host factors. Patients with aspiration pneumonitis secondary to seizure, head trauma, or drug overdose should be inspected for signs related to these processes. In addition to exhibiting signs associated with the underlying disease that led to their aspiration, patients with aspiration pneumonia or pneumonitis may demonstrate the following:  Fever or hypothermia  Tachypnea  Tachycardia  Decreased breath sounds  Dullness to percussion over areas of consolidation  Rales  Egophony and pectoriloquy  Decreased breath sounds  Pleural friction rub  Altered mental status  Hypoxemia  Hypotension (in septic shock) Chemical pneumonitis Patients with chemical pneumonitis may present with an acute onset or abrupt development of symptoms within a few minutes to two hours of the aspiration event, as well as respiratory distress and rapid breathing, audible wheezing, and cough with pink or frothy sputum. Findings on physical examination may include tachypnea, tachycardia, fever, rales, wheezing, and possibly cyanosis. Bacterial aspiration pneumonia The presentation of bacterial aspiration pneumonia is similar to that of community-acquired pneumonia (CAP) and may include nonspecific symptoms including headache, nausea/vomiting, anorexia, and weight loss. The onset of illness may be subacute or insidious, with the symptoms manifesting in days to weeks when anaerobic organisms are the pathogens. The patient may also describe the following:  Cough with purulent sputum  Fever or chills   Malaise, myalgias  Rigors may be present or absent  Shortness of breath, dyspnea on exertion  Pleuritic chest pain  Putrid expectoration (a clue to anaerobic bacterial pneumonia) In hospital acquired aspiration pneumonia, the symptoms of cough and shortness of breath of may be more acute in onset than in CAP when aerobic organisms are the pathogens. Fever and rigors may be present. Patients brought in after witnessed large-volume vomitus and subsequent aspiration pneumonitis may have a history consistent with an acute change in mental status, which may include seizure, alcohol abuse, drug overdose, and/or head trauma. On physical examination, findings may include periodontal disease (primarily noted as gingivitis), bad breath, fever, bronchial breath sounds and rales over a consolidated posterior area. Diagnosis in Aspiration Pneumonia Clinicians must consider the diagnosis of aspiration pneumonia when a patient presents with risk factors and radiographic evidence of an infiltrate suggestive of aspiration pneumonia (see Predisposing Conditions for Aspiration Pneumonia). The location of the infiltrate on chest radiograph depends on the position of the patient when the aspiration occurred and is discussed further in the Chest Radiography section. The laboratory studies obtained should be guided by the patient’s clinical presentation (see Presentation of Aspiration Pneumonia). Patients with signs or symptoms of sepsis or septic shock require further laboratory testing than those with uncomplicated aspiration syndromes. Differentials When evaluating a patient with suspected aspiration pneumonia, other considerations include necrotizing pneumonia, bronchopleural fistula, lung carcinoma, lung abscess, mycoses, and hypersensitivity pneumonitis. In children, bronchiolitis, croup or laryngotracheobronchitis, epiglottitis, asthma, reactive airway disease, respiratory distress syndrome, and foreign bodies should be considered. In addition, assess for the following conditions:  Acute respiratory distress syndrome  Tuberculosis  Bronchitis  Chronic obstructive pulmonary disease and emphysema  Adult epiglottitis  Pneumonia, empyema and abscess   Pneumonia, Immunocompromised  Mycoplasma pneumonia  Viral pneumonia  Septic shock Prehospital Management of Aspiration Pneumonia Prehospital care should focus on stabilizing the patient's airway, breathing, and circulation. In patients found with signs of gastric aspiration (ie, vomitus) suctioning of the upper airway may remove a significant amount of aspirate or potential aspirate. Intubation should be considered in any patient who is unable to protect his or her airway. The ability of paramedics to provide this intervention depends on the level of their training. In addition, emergency medical technicians (EMTs) trained in intubation may choose to intubate patients with poor gag reflex to prevent aspiration. Other measures include the following:  Oxygen supplementation  Cardiac monitoring and pulse oximetry  Intravenous (IV) catheter placement and IV fluids, as indicated Emergency Department Management Emergency department care should start with stabilizing the patient's airway, breathing, and circulation. Oropharyngeal/tracheal suctioning may be indicated to further remove aspirate. Reassess the need for intubation on a frequent basis depending on the patient’s oxygenation, the patient's mental status, signs of increased work of breathing, or impending respiratory failure. Continue supplemental oxygenation as needed, as well as continue cardiac monitoring and pulse oximetry and provide continued supportive care with intravenous fluids and electrolyte replacement. Inpatient Management Patients with aspiration pneumonia, both chemical pneumonitis (chemical pneumonia) and bacterial pneumonia (bacterial pneumonia), need inpatient care for several reasons, including the acuity of illness, host factors, and the uncertain course and prognosis of aspiration pneumonia. Patients with severe hemodynamic compromise and/or persistent respiratory distress should be admitted to the intensive care unit (ICU). Intubated and ventilated patients must be transferred to a hospital with an ICU, as well as patients with signs or symptoms indicating severe sepsis or septic shock. Patients with stable respiratory and hemodynamic status can be managed on a general-care floor. Complications Complications of aspiration include acute respiratory failure, acute respiratory distress syndrome (ARDS), and bacterial pneumonia. Complications of bacterial pneumonia include parapneumonic effusion, empyema, lung abscess, and suprainfection. Bronchopleural fistula is also a complication. Aspiration pneumonitis can rapidly progress to respiratory failure. Consultations Consult with a pulmonologist for bronchoscopy when airway obstruction due to a foreign body is suspected in patients with chemical pneumonitis or for ruling out a neoplasm in bacterial pneumonia cases. Consult with an intensivist (critical care specialist) for severe chemical pneumonia if hypoxemia is severe and ventilatory support is anticipated. [20, 21] Consult with a thoracic surgeon for bacterial pneumonia complicated by empyema (eg, closed-tube drainage, open-tube drainage, and decortication). In general, there is no role for surgical care, except in such cases with complications. Consult with an infectious disease specialist for advice about proper antibiotic therapy. Consult with a speech and language therapist for a comprehensive swallowing evaluation in patients with stroke or other risk factors for aspiration. These therapists can perform a bedside swallowing evaluation and, if abnormalities are found, can teach the patient compensatory strategies with soft or pureed foods and thickened liquids.