Answer to patient : Almost half of healthy adults routinely aspirate small volumes of oral or stomach contents (see questions 4 and 5 below) during sleep. Several important conditions and risk factors predispose patients to aspiration. Patients at risk can be divided into the young adult population versus a more elderly and dependent population.

It is perhaps easier to think of elderly patients in terms of those residing in the community versus those residing in nursing homes. In general increasing age is an independent risk factor for aspiration. With age, the body becomes frail, loses coordination, and may develop weaknesses such as outpouchings in the upper digestive tract that can “hide” or sequester food and later cause regurgitation (vomiting) of food leading to aspiration. Older patients also have a higher risk for having acid reflux disease (heartburn) that is associated with an increased risk for aspiration.

Another important group of patients at risk for aspiration pneumonia are patients on long-term acid-suppressive medications (such as omeprazole, zantac). These medications work to suppress the acidic contents of the stomach in an attempt to prevent injury when acidic stomach contents reflux—however they also allow harmful bacteria to flourish within the stomach environment. Without stomach acid, these bacteria are more readily able to cause pneumonia after aspiration takes place.

(1–2-min evidence-based reading for clinician): Epidemiology, genetics and pathophysiology, diagnostic test results, treatment options, etc.

Some degree of aspiration is inevitable—and even “normal.” As described in detail later in this chapter, almost half of healthy normal adults aspirate routinely during the night. However, several structural and functional abnormalities in the aerodigestive tract place certain populations at a higher risk for aspiration.

For elderly patients living in the community, a risk for aspiration may stem partly from the physical age-related changes that take place in the human body. Structural abnormalities such as cervical osteophytes (bony outgrowths of the vertebra indenting the oropharyngeal tract) [8], Zenker’s diverticula (pharyngeal outpouching representing weakened muscular spots) [9], and esophageal strictures and webs [10] can lead to misdirection of the food bolus and hence aspiration. Gastroesophageal reflux disease (GERD) is also more common in the elderly and increasing age correlates with the severity of GERD and its complications (erosive esophagitis, Barrett’s esophagus) [6, 11].

To demonstrate this increased risk, Kikuchi et al. studied 14 otherwise healthy elderly patients (averaging 77 years) hospitalized with community-acquired pneumonia and compared their aspiration events with age-matched controls without pneumonia. They concluded that elderly patients hospitalized with community-acquired pneumonia were seven times more likely to have aspirated than their age-matched controls (71 vs. 10%) [12]. Other studies too have correlated increasing age (independent of neurological disease) with a higher incidence of impaired oropharyngeal deglutition [13]. Based on these observations, one may argue that age (and associated physiological changes in the body) alone is a risk for aspiration [14].

Institutionalized elderly patients are a different story. They are reported to suffer from poor oral hygiene and care [15, 16] and harbor serious pathogens (Enterobacteriaceae, Pseudomonas aeruginosa, and Staphylococcus aureus) in their oral cavity [6]. In a study on the dental health of patients living in 55 residential homes in the United Kingdom, large numbers of patients were found to have an increased incidence of oral ulcers, glossitis, and coronal and root caries [16]. Consequently, improving oral care is shown to reduce the incidence of pneumonia by almost one and a half times in such groups [17].

The institutionalized elderly are also more likely to suffer from neurological complaints or use of medications that impair swallowing. An interesting study of 1946 patients found that 10% of patients with community-acquired pneumonia and 30% of patients with continuing-care facility (CCF)-associated pneumonia were due to aspiration [18]. Amongst the CCF-pneumonia group, as many as 72.4% of patients had dysphagia secondary to a neurological disease (i.e., stroke, dementia, multiple sclerosis, mental retardation, brain tumors, movement, Parkinson’s disease, and Alzheimer’s disease) that posed a risk for their aspiration. In addition many of the CCF patients were taking centrally acting medications that could cause sedating or xerogenic (drying) effects reducing salivary flow [18]. Depending on the methods used, up to 78% of patients who have had a stroke exhibit dysphagia and may aspirate at least in the acute phase after a CVA [19].

For adults with community-acquired pneumonia it appears that factors that lead to an altered or a decreased level of consciousness (i.e., alcohol use, 12.9%; drug overdose, 21.3%; or hepatic encephalopathy 7.7%) are the main risk factors leading to aspiration [18, 20].

Other risk factors in the community affecting all ages include the aggressive use of acid-suppressive medications (such as proton pump inhibitors (PPIs) and H2 receptor blockers). Approximately 40–70% of medical inpatients receive acid-suppressive medications and as many as 50% are new prescriptions. PPIs are linked with an almost 1.5–1.89 times higher risk for community-acquired pneumonia [21, 22]. In a large hospital-based epidemiological cohort, use of PPIs was associated with 30% increased odds of hospital-acquired pneumonia (HAP) in non-ventilated patients and this risk was highest within the first few days to a week of PPI use [23]. Acid suppression allows survival of bacterial pathogens (that would normally be killed in acidic contents). Reflux and further aspiration events allow these pathogenic bacteria to find their way into the lungs and cause infection.

This risk from acid suppression has also been demonstrated in critically ill, mechanically ventilated patients. In a randomized controlled trial, patients were assigned to use of sucralfate, antacid, or H2 receptor blocker use. The group with sucralfate use was demonstrated to have significantly lower rates of gastric colonization and late-onset pneumonia (4 days later) when compared to the antacid and H2 blocker groups [24]. These data support the hypothesis that suppression of gastric pH leads to higher rates of gastric bacterial colonization and higher rates of hospital-acquired pneumonia [25] and current guidelines recommend against use of stress ulcer prophylaxis in patients without a clear indication for their use [26].

Answer to patient : As described earlier, small-volume aspiration takes place routinely in almost half of healthy normal adults. About 15% of patients in the community setting develop pneumonia as a result of aspiration and aspiration pneumonia is associated with worse survival than other community-acquired pneumonias .

Larger volume aspiration pneumonia is also the second most common reason for nursing home patients to require admission to a hospital and is the leading cause of death in this group of patients. Aspiration complicates 1 of every 3000 cases of general anesthesia and continues to be not only a significant financial burden on health care costs but also associated with high rates of death.

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Aspiration is very common and can occur in both health and disease. The incidence depends on the methods used to detect aspiration, with some sensitive techniques detecting clinically insignificant “microaspirations ” while others (e.g., swallow studies) identifying larger boluses of material passing the vocal cords (see question 4 for details). Huxley et al. studied aspiration in 20 normal and 10 patients with depressed consciousness by injecting indium¹³¹ chloride (radioactive tracer) via a catheter directed into their nasopharynx. Radioactive tracer uptake was seen on post-sleep lung scans (as evidence of nocturnal aspiration) in 45% (9 out of 20) of healthy subjects and 7 out of 10 (70%) patients with depressed consciousness during sleep [20].

In a similar experiment, Gleeson et al. also studied aspiration events in ten healthy adults using radioactive tracer uptake in lungs and sleep patterns using sleep polysomnography over two separate nights [27]. Radioactive tracer solution was instilled in the nasopharynx of all subjects during nocturnal sleep. Although no particular sleep behavior (time spent in bed, sleep efficiency, supine sleep time, etc.) was associated with a higher risk, it was demonstrated that 5 of 10 (50%) healthy subjects silently aspirate on at least one of every two nights while asleep.

However, as described earlier, certain populations are much more likely to aspirate and suffer from clinical consequences of this aspiration.

Epidemiological studies indicate that approximately 5–15% of all community-acquired pneumonia is secondary to aspiration [6]. Aspiration pneumonia has a significantly higher 30-day mortality (21%) when compared to community-acquired pneumonia and patients are more likely to be admitted to the intensive care unit (ICU) and require mechanical ventilation [28].

Aspiration pneumonia has been reported to be the second most frequent principal diagnosis amongst Medicare patients [29]. Amongst nursing home residents aspiration pneumonia is the second most common infection (21%) after urinary tract infections, has an annual incidence of new cases between 18 and 48%, and has a higher mortality rate than that of any other nosocomial infection [30].

Aspiration is also well recognized as a complication of general anesthesia occurring in 1 of every 2000–3000 cases in adults [31]. Anesthetic agents can suppress airway protective reflexes and predispose patients to aspiration. Aspiration pneumonia accounts for as many as 10–30% of all deaths associated with anesthesia [6, 32].

It comes as no surprise that “aspiration pneumonia” is considered by some to be an epidemic. Admission rates and health care costs for patients with the diagnosis have risen rapidly. Aspiration pneumonia is associated with longer hospital stays (mean increase of 9 days), increased total hospital charges (mean increase of $22,000), higher ICU admission rates (odds ratio 4.0), and a higher in-hospital mortality (OR; 7.6) [30, 33].

Answer to patient : Some aspiration has no signs or symptoms, and thus is called “silent.” When present, symptoms of aspiration can range from subtle, unexplained coughing that persists over several weeks to wheezing similar to that seen in asthma. Choking may be obvious when a patient eating suddenly develops breathing difficulty and distress for no other clear reason. Aspiration may occur in small amounts ( microaspiration ) and go unwitnessed or be obvious when a patient actively vomits and inhales contents into his/her lungs ( macroaspiration ).

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Aspiration may be asymptomatic (silent or unwitnessed) or symptomatic (micro- or macroaspiration). Microaspiration refers to aspiration of small amounts of gastric contents or oropharyngeal secretions (usually <1 mL). Macroaspiration , on the other hand, refers to the visible aspiration of large amounts of bowel or gastric contents [7]. Signs of acute aspiration include sudden choking, shortness of breath, or chest pain while eating. Most adults, however, are likely to have subtle symptoms—such as a chronic unexplained cough or wheezing.

A diagnosis of aspiration pneumonia requires a high index of suspicion and can be challenging.

Historically bedside evaluation of swallowing has evolved from the care of patients suffering from stroke and resultant dysphagia [19].

A direct observation of swallowing; special attention to certain indicators of altered swallowing such as decreased consciousness, dysarthria, coughing, or choking while eating; and presence of a weak and delayed cough in response to aspiration can alert the physician to a potential problem. However, bedside evaluations are insensitive [6, 34]. In a study by Smithard et al., bedside clinical assessment had a sensitivity of only 47–70% (depending on who performed the assessment) and missed approximately 30–53% aspirators [34]. Such patients are likely to silently aspirate (without any overt signs of distress) and evaluation of ineffective swallowing for these patients must be combined with objective instrumental tests.

A modified barium swallow study (MBSS) or video fluoroscopic swallow (VFS) is a noninvasive test that reviews the oral, pharyngeal, and cervical esophageal stages of swallowing while the patient is upright and swallowing varying consistencies of barium-coated or water-soluble contrast mediums. This test is performed by speech therapists in conjunction with radiologists who acquire a video of swallowing to help elucidate a physiological reason for dysfunctional swallowing. This test has been traditionally considered a gold standard for diagnosing dysphagia .

A barium swallow is conducted by the radiologist while the patient is upright or, less commonly, supine. The esophageal phase of swallowing is observed for any structural or motility etiologies as a causation of aspiration.

FEES (or flexible endoscopic evaluation of swallowing ) was first described in 1988 by Langmore et al. [35]. This modality can be performed by a trained speech therapist and involves viewing the oropharyngeal and laryngeal phases of swallowing via a nasally inserted laryngoscope. A FEES has several parts to it. First a preliminary assessment of anatomy is conducted and the movement of structures inside the mouth in response to secretions, etc. is observed. The second part includes observing the patient to swallow meals of varying consistencies and bolus sizes of liquids and solids. This allows the examiner to try several different combinations of consistencies and volumes and different strategies to determine which is handled best by an individual patient. Laryngeal penetration (appearance of contrast in the laryngeal vestibule) and aspiration (food below the vocal cords) can be identified using this technique. The esophageal phase cannot be assessed using this technique. This test is portable and can easily be conducted in the patient’s home environment with family/caregiver participation [14].

Lastly, esophagogastroduodenoscopy (EGD) is an invasive test that can be performed by a gastroenterologist and can help identify mucosal and other structural abnormalities along the esophageal tract.

Studies evaluating the consistency of results using FEES versus video fluoroscopy (VFS/modified barium swallow (MBSS) suggest a great degree of agreement between the two tests. A study on 21 patients by Langmore et al. [36] evaluating four features (aspiration, penetration, spillage, and residue) concluded that FEES agreed with the results of video fluoroscopy in 90% of cases (sensitivity 0.88, specificity 0.5, positive predictive value 0.69, negative predictive value 0.63). In general both tests complement one another and are considered “therapeutic” in that they allow a greater patient feedback during the test and real-time modification of behavioral strategy and bolus type—in order to achieve the most effective, safest swallowing. FEES may be considered superior for patients with severe dysphagia who have not had any oral intake for several weeks [14].

Answer to patient : Harmful effects of aspiration depend on the amount and nature of the materials aspirated. Aspiration of acidic liquid stomach contents can lead to an inflammation of the smaller airways that presents with wheezing and shortness of breath—very similar to the tell-tale signs of asthma.

Aspiration of solid contents such as solid foreign objects can lead to a blockage of one of the main or central airways leading to asphyxiation or choking. Aspiration of a foreign object is considered a medical emergency as it can lead to death. It requires urgent steps to remove the aspirated materials. Recently aspirated iron tablets or potassium pills have become a focus of attention as these are particularly corrosive (causing chemical burn) and can seriously damage the lining of the airways. If a foreign object is not promptly removed, it can lead to long-term problems of causing stenosis (narrowing) of the bronchial tubes as well as formation of fistulae (abnormal connection between the lungs and other organs) that are extremely difficult to repair and treat.

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Aspiration can result in several different clinical syndromes—and pH and volume of aspirated contents are critical determinants of the degree of lung injury [6, 37]. Both micro- and macroaspiration can result in immediate and long-term injury to the lungs.

Some acute consequences of aspiration include aspiration pneumonitis, aspiration pneumonia, and asphyxiation (or choking).

Aspiration or chemical pneumonitis (also known as Mendelson’s syndrome ) was described in 1946 while observing obstetric patients undergoing general anesthesia. Patients suffered from an acute asthma-like reaction likely from aspiration of liquid contents. By instilling 0.1 N hydrochloric acid into rabbit lungs, Mendelson elicited a pattern of lung injury similar to that seen in humans and highlighted the importance of acidic gastric contents in causing acute lung injury or pneumonitis [38]. Since then several experiments have shown that neutralizing acidic contents of aspirate can mitigate the extent of lung injury [6]. Most authors agree that a volume of more than 20–25 mL and a pH less than 2.5 are critical to causing chemical pneumonitis in adults [6, 37–39]. Studies in rats have demonstrated this to be a biphasic process. There is an initial phase of intense direct chemical burn from acidic contents causing increased capillary permeability and leakage—followed by a quiescent period over the next 2–3 h. At 4 to 6 h an aggressive neutrophilic response peaks and the release of inflammatory mediators leads to lung injury much like the adult respiratory distress syndrome (ARDS) [37].

It is important to differentiate aspiration pneumonitis from pneumonia—as the latter involves pathogenic bacteria development of a distinct radiographic infiltrate in a patient at risk for aspiration and entails antimicrobial therapy.

Table 17.1 depicts differentiating points between aspiration pneumonia and pneumonitis .

In general a bacterial infection is not thought to play a primary role early in the process of aspiration as acidic contents suppress gastric flora. During silent aspiration adults aspirate volumes in the range of 0.01–0.2 mL [27] and although this may introduce bacteria in sufficient amounts (10⁴–10⁵ organisms per milliliter) [27, 40] host defenses are usually able to combat disease. Bacterial infection (aspiration pneumonia) develops in situations where host defenses are compromised (impaired glottis closure, cough reflex, acid suppression with medications, impaired ciliary clearance, depressed humoral or cell-mediated immunity) or when a bacterial inoculum is large and deleterious enough to overwhelm defenses [6].

Aspiration of solid components (foreign-body aspiration or FBA) is more common in children and adults with advanced age. In 2014, approximately 4864 people died from choking in the United States and 2751 of them were over the age of 75 [41]. Acute aspiration of a large FB into a central airway can result in asphyxiation and even death—and requires immediate intervention to relieve obstruction. Depending on the size, type, and location of aspirated contents patients can develop serious long-term consequences such as recurrent post-obstructive pneumonias, hemoptysis, and bronchial stenosis from chronic obstruction. Pills (iron and potassium chloride tablets in particular) are being increasingly recognized for causing extensive chemical burn and inflammation in the bronchial epithelium [42, 43].

Answer to patient : Unfortunately, aspiration can harm us in both the short and the long term. The chronic, repetitive damage from inhalation of acidic stomach contents and bacteria can lead to chronic lung conditions such as bronchiectasis. Bronchiectasis refers to an abnormal enlargement (dilation) of the smaller airways that leads to a difficulty in clearing mucus and secretions. This in turn can become a nidus for infections.