Cori L. Daines
Pulmonary aspiration is defined as the passage of foreign material or fluid into the lungs during inspiration. Pathologic aspiration events can be divided into 2 main categories: acute and chronic. Acute events include large-volume aspiration of gastric contents, hydrocarbon aspiration, near-drowning, and foreign body aspiration. Chronic events include recurrent, small-volume aspiration of saliva, food, upper airway secretions, or gastroesophageal reflux. Large-volume aspiration events are usually witnessed, but recurrent small-volume aspirations are often silent and more difficult to diagnose and manage. It is important to recognize the risk factors to properly diagnose aspiration (Table 511-1).
ACUTE ASPIRATION
ASPIRATION OF FOREIGN BODIES
Airway foreign body aspiration is an important cause of respiratory distress in children, especially those under 3 years of age. Food is the most common foreign body found in the airways of toddlers, while nonfood items are more common in older children and adolescents.4 Presenting symptoms include cough, wheeze, shortness of breath, and fever, sometimes temporally associated with a witnessed episode of choking. The object should be removed with rigid bronchoscopy, which maintains control of the airway and facilitates ventilation. Although fiberoptic bronchoscopy can examine more distal areas of lung, the inability to ventilate and maintain airway patency with a flexible fiberoptic broncho-scope renders this procedure inadequate for foreign body removal. Complications, especially if the object has been present for a long time, may include pneumonia, abscess formation, bronchiectasis, or granulation tissue in the airway. The details of foreign body aspiration diagnosis, pathogenesis, and management are discussed in detail in Chapter 506.
NEAR-DROWNING
Near-drowning is estimated to occur 3 to 10 times more commonly than drowning, and pulmonary sequelae are common.6 Most children with near-drowning aspirate water into their lungs,7 leading to pulmonary edema, pneumonia, and sepsis. Most survivors have normal pulmonary function testing in follow up. The details of near-drowning pathogenesis, management, and outcomes are discussed in Chapter 117.
HYDROCARBON ASPIRATION
Aspiration of hydrocarbons, including solvents, paints, paint removers, turpentine, and petroleum distillates, remains a significant accidental problem, especially in young children (see also Chapter 120). The physiologic effects are dependent on the properties of the hydrocarbon and can consist of central nervous system depression, gastrointestinal irritation with edema or ulceration, cardiac arrhythmias or cardiomyopathy, and pneumonitis. The hydrocarbons with the highest potential of causing aspiration injury are those with low viscosity, low surface tension, and higher volatility. Chest radiograph findings may be present as early as 20 minutes or as late as 24 hours after aspiration. Clinical findings consist of tachypnea, retractions, cough, grunting, and fever.14 It is important to observe children for at least 6 to 8 hours after a suspected aspiration, to follow serial chest radiographs, and to admit any child with respiratory symptoms or abnormal chest films for observation. There is a risk for secondary aspiration with emesis of material with hydrocarbons, so inducing emesis in these children should be avoided.15 Management is supportive as well as treatment of complications as indicated. Most children recover without significant complications, although death does still occur.
LARGE-VOLUME ASPIRATION
PATHOPHYSIOLOGY
The critical volume of aspirate seems to be 0.8 mL/kg to cause pneumonitis,17 although acidic or caustic materials can cause damage with less volume than more neutral fluids. This pneumonitis consists of desquamation of the epithelium of the bronchi, bronchioles, and alveoli; edema; and hemorrhage. Repair of the epithelium may require 2 to 3 weeks, but scarring, chronic inflammation with lymphocytes, and even bronchiolitis obliterans may occur.18
Table 511-1. Risk Factors for Aspiration
|
Depressed consciousness |
|
General anesthesia or sedation |
|
Medication |
|
Drug intoxication |
|
Seizure |
|
Head trauma |
|
Mechanical |
|
Nasogastric or orogastric tube |
|
Endotracheal tube |
|
Tracheostomy tube |
|
T-tube |
|
Anatomical |
|
Craniofacial syndromes (CHARGE, Möbius, West, CHAOS, Pfeiffer, etc.) |
|
Cleft palate |
|
Micrognathia |
|
Macroglossia |
|
Laryngomalacia |
|
Laryngeal web |
|
Laryngeal cleft |
|
Vocal cord paralysis |
|
Subglottic or tracheal stenosis |
|
Tracheoesophageal fistula |
|
Tracheobronchomalacia |
|
Achalasia |
|
Esophageal web or stricture |
|
Eosinophilic esophagitis |
|
Gastroesophageal reflux |
|
Collagen vascular diseases |
|
Tumors, masses (compressing airway) |
|
Neuromuscular |
|
Prematurity with immature swallow |
|
Cerebral palsy |
|
Developmental delay |
|
Chromosomal abnormalities |
|
Hydrocephalus |
|
Increased intracranial pressure |
|
Arnold-Chiari malformation |
|
Muscular dystrophy |
|
Spinal muscular atrophy |
|
Myotonic dystrophy |
|
Myasthenia gravis |
|
Guillain-Barre syndrome |
|
Werdnig-Hoffmann disease |
|
Respiratory distress |
CLINICAL MANIFESTATIONS AND DIAGNOSIS
Without a witnessed event, the clinical symptoms on presentation vary depending on the quantity of aspirate and the nature of the aspirate. The symptoms that should raise concern are abrupt dyspnea, fever, cyanosis, hypoxemia and diffuse crackles. Diagnosis is made on the basis of typical symptoms, physical examination, and radiographic findings in an at-risk individual.
TREATMENT
Once the aspiration event has occurred, the airway epithelial damage is present, like a burn. There is no way to neutralize the acid to prevent injury.18 If the material aspirated was particulate, flexible or rigid bronchoscopy may be useful to remove the particulate matter; otherwise, the management is largely supportive. Supplemental oxygen for hypoxemia, mechanical ventilation for respiratory failure, and intravenous fluids to support vascular volume are all indicated. Generally, steroids are not recommended.27 Empiric antibiotic use is common, but antibiotics are not helpful unless treating a superimposed bacterial infection. Supplemental chest percussion and postural drainage may be useful if there is atelectasis or pneumonia.
COMPLICATIONS AND OUTCOMES
The most common complication is that of bacterial suprainfection. This complication is seen more frequently in individuals with a predisposing risk factor (Table 511-2). Clinically, some children have increased or new fever, worsening respiratory symptoms with cough, wheeze, crackles or respiratory distress, increased leukocytosis, or new findings on chest radiograph. Initial treatment should be with penicillin, ampicillin, and antibiotics geared toward anaerobes. If the aspiration pneumonia has occurred in an individual with significant underlying medical problems, additional treatment with second- or third-generation cephalosporins may be warranted. Mortality rates are about 5% despite best clinical management.
PREVENTION
Prevention revolves around managing the known risk factors. Treatment of gingivitis or tooth decay should occur promptly. In hospitalized patients, endotracheal tubes or enteral feeding tubes should be removed as soon as medically feasible. Maintaining low gastric volumes may help prevent gastroesophageal reflux (GER). Balancing risks and benefits of gastric acid suppression is important because acid suppression may lead to bacterial overgrowth in gastric contents.
Table 511-2. Risk Factors for Superimposed Bacterial Infections in Aspiration
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Pneumonitis |
|
Periodontal disease |
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Tooth decay |
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Gastric outlet or intestinal obstruction |
|
Prolonged hospitalization |
|
Endotracheal intubation |
|
Enteral tube feeding |
|
Immunosuppression |
|
Chronic gastric acid suppressive therapy |
CHRONIC RECURRENT SMALL-VOLUME ASPIRATION
Recurrent or chronic pulmonary aspiration (CPA) describes the recurrent passage of food, gastric contents, or saliva into the airway, resulting in symptoms such as cough, wheeze, choking, pneumonia, or lung damage.35-40 CPA may occur only sporadically in some children, when other stressors, such as upper respiratory tract infections, are also present. Often, more than 1 mechanism of CPA is present, complicating diagnosis and management. It is often difficult to determine if CPA is causing lung disease. The 3 main mechanisms of CPA are (1) swallowing dysfunction resulting in the direct aspiration of food, (2) GER and aspiration, and (3) failure to protect the airway from oral secretions, resulting in the aspiration of saliva and oral contents.
ASPIRATION DUE TO SWALLOWING DYSFUNCTION
Normal swallowing is a complex activity that involves a multitude of voluntary and involuntary actions. Any abnormality in the complex sequence of events can result in aspiration. Swallowing dysfunction occurs most frequently in individuals with neurologic disorders or any of the predisposing factors listed in Table 511-1, but it should be considered in any child with suspicious symptoms.
PATHOPHYSIOLOGY AND CLINICAL MANIFESTATIONS
Typical symptoms of aspiration due to swallowing dysfunction include coughing, wheezing, choking, and gagging that is temporally related to the intake of food. It may be intermittent, occurring only at times of stress such as during upper respiratory tract infections; it may be positional, and it often changes over time with growth and development, or it may be silent. Repeated bouts of direct aspiration can lead to recurrent bronchitis or pneumonia and bronchiectasis as well as chronic hypoxia and dyspnea.
The pathophysiology of lung damage arises from the inflammatory cascade triggered by the aspiration. There is no difference in the extent of neutrophilic infiltration between acidic (from stomach acid) and neutral (direct aspiration) aspirated food.42
Diagnostic Evaluation
The approach to the evaluation and treatment of children with swallowing dysfunction is discussed in detail in Chapter 31.
ASPIRATION OF GASTROESOPHAGEAL REFLUX
GER occurs occasionally in almost everyone when food mixed with gastric contents moves in a retrograde manner from the stomach through the lower esophageal sphincter into the esophagus. It is common in infants under a year old, but it is rarely pathologically symptomatic (see also Chapter 394).
PATHOPHYSIOLOGY AND CLINICAL MANIFESTATIONS
Acid is irritating and induces inflammation in the airway.3,18 There is evidence that GER is associated with respiratory symptoms such as cough, wheeze, pneumonia, and apnea.76-78 A causal relation between GER and respiratory symptoms due to aspiration is much more difficult to prove.79-81 We know that stimulation of esophageal receptors by GER can cause reflex bronchospasm, cough, and wheeze without actual aspiration of GER.82 The challenge is to determine whether GER is pathological and if aspiration in occurring.
DIAGNOSIS
Esophageal pH or Impedance Monitoring Esophageal pH monitoring is considered the gold standard for detecting GER (Chapter 394). It detects drops in pH, indicating the presence of acid from the stomach in the esophagus. It cannot, however, detect nonacid reflux and must be performed in individuals not on acid suppressive medication.86,87
Multichannel intraluminal impedance with pH monitoring (MII-pH) is a newer technique that has certain advantages of traditional pH monitoring. It can track the movement of gas or liquid boluses, both anterograde and retrograde; detect both acid and nonacid liquid boluses; determine if the bolus is being swallowed or refluxed; and determine how high along the esophagus the bolus moves.88 Unfortunately, MII-pH is not yet widely available.
Both pH and MII-pH studies will diagnose GER, but neither study can detect aspiration.
Upper Gastrointestinal Series/Barium Esophagram This simple test detects the presence of reflux of swallowed barium. Its advantages are that it is simple, inexpensive, and quick. Unfortunately, it captures GER and aspiration only if it occurs during the study, and it cannot quantify the frequency of such events.
Flexible Bronchoscopy with Bronchoalveolar Lavage The presence of lipid-laden macrophages obtained during bronchoscopy is used most often as evidence of aspiration due to GER. Finding lipid, however, in the lower airways does not help determine whether the lipid came from GER or from direct aspiration due to swallowing dysfunction.
Gastroesophageal Scintigraphy/“Milk Scan” In this study, technetium Tc99 is mixed with a child’s milk or food and the child is allowed to eat. Serial radiologic images are then captured to detect tracer in the lungs. Unless images are obtained frequently during and after the mealtime, or if the child is fed via a gastrostomy, this test does not clearly distinguish between aspiration from swallowing and aspiration from GER. Some studies suggest that obtaining images 24 hours following the radio-label meal improves sensitivity for GERD.96-99
TREATMENT
Treatment of GERD is discussed in detail in Chapter 394. Options include medical therapy using thickened feedings or pharmaceutical agents that reduce gastric acid secretion or improve esophageal clearance; surgical therapies such as fundoplication; jejunal drip feedings to prevent GER; and finally gastroesophageal dissociation in children that are highly unlikely to achieve oral feeding. These approaches are discussed in detail in Chapter 394.
SALIVARY ASPIRATION
Aspiration of saliva is the most insidious type of aspiration. Some nocturnal aspiration of saliva can occur in healthy individuals,2 so understanding when aspiration of saliva is pathological is key to prevention of complications. Recognizing symptoms and having a high index of suspicion, especially in high-risk children (Table 511-1), will help prevent poor outcomes.
PATHOPHYSIOLOGY AND CLINICAL MANIFESTATIONS
The clinical symptoms of aspiration of oral secretions include choking and gagging as well as chronic or intermittent cough and wheeze and recurrent pneumonia. Additionally, these children often have sialorrhea with drooling and pooling of saliva in the mouth. They often have overt choking on their saliva and may improve when positioned so saliva runs out of the mouth. Many of these children are developmentally delayed, although cranial nerve palsies, vocal cord paralysis, laryngoesophageal cleft, and craniofacial abnormalities also lead to inability to handle saliva appropriately. In these children, their swallowing is severely dysfunctional, not allowing them to swallow saliva appropriately, and their laryngeal sensation is abnormal, not allowing them to protect their airway adequately.120 Saliva contains bacteria and yeast that are potentially pathological to the lungs if aspirated in large enough quantities or frequently. Recurrent pneumonia or even pulmonary abscesses are possible.31
DIAGNOSIS
In children with suspected aspiration and either treated or absent GER, who are being fed parenterally, these diagnostic tests are essential. In children with potentially confounding causes of aspiration, these tests may be necessary or should be performed concomitantly with others to rule out other forms of aspiration.
Radionuclide Salivagram/“Spit Scan” This test is often considered the gold standard for detection of salivary aspiration. Similar to gastroesophageal scintigraphy, this test involves using a small amount of oral radiotracer.121,122Subsequent detection in the lower airways or lungs can diagnose aspiration of the oral secretions.
Studies have shown positive salivagrams in 26% to 28% of children suspected of aspirating oral secretion. However, many children who might, at least intermittently, aspirate their saliva are missed with this test.
FEES with Sensory Testing (FEEST) FEES allows direct visualization of the larynx with observation of swallowing. Pooling of secretions and penetration or aspiration of oral secretions can be seen with a small amount of oral dye added. Sensory testing involves graduated puffs of air delivered to the larynx to determine the threshold necessary to induce protective laryngeal reflexes and can help distinguish those at risk for aspiration.
TREATMENT
The first line of therapy for aspiration of saliva is pharmacological to reduce salivary flow. Some studies have evaluated behavioral modification to control drooling, with positive results, but none of these actually decrease salivary flow.131,132 Salivary flow reduction can be accomplished by anticholinergics. Glycopyrrolate administered orally at a dose of 0.04 to 0.1 mg/kg/dose will reduce saliva but glycopyrrolate is also associated with anticholinergic side effects. Using antihistamines such as cetirizine for drooling has had anecdotal success. Scopolamine patches tend to be more successful than antihistamines, with few side effects.136,137 Because treatment is usually accomplished with a patch, titration can be difficult. Generally, a single patch is applied every 72 hours, although partial patches have also been tried. No studies have shown that medical treatment actually prevents aspiration or resultant lung damage even though it reduces salivary flow.
Botulinum toxin injection into the salivary glands can paralyze the glands and reduce saliva production. Repeat therapy as required since the toxin wears off; no long-term studies of efficacy of repeated doses have been done. There has not been any study of the impact of botulinum toxin injection on aspiration or lung disease.
Surgical options include ligation of salivary ducts or removal of certain salivary glands. This therapy can serve to permanently decrease salivary flow. Ligation of the ducts of the parotid and submandibular glands or excision of the submandibular glands and ligation of the parotid ducts has been used with good success in children.141-144 Two studies have also shown a reduction in hospitalizations and lower respiratory tract infections in children who have undergone the procedures.141,143
Another option is insertion of a tracheostomy tube. This alone cannot prevent aspiration. It does allow for suctioning of aspirated saliva to hopefully prevent pneumonia. If a child is placed on positive pressure ventilation, aspiration may be less likely because of the positive pressure in the lower airway impeding passive influx of saliva.
The definitive treatment for salivary aspiration is physical separation of the upper airway from the lower airway.147-150 This is accomplished by a separation of the larynx from the trachea with the trachea diverted to a permanent stoma. This surgery will prevent aspiration of saliva, but it will prevent phonation. It should be considered in children with intractable aspiration who are experiencing progressive lung damage or life-threatening pneumonias.
RADIOGRAPHIC DIAGNOSIS OF RECURRENT ASPIRATION
Radiographic testing is not diagnostic of recurrent pulmonary aspiration and cannot distinguish among the types of aspiration. It can, however, give evidence of pulmonary inflammation or damage and help us to assess the pulmonary impact of the aspiration.
FIGURE 511-1. A chest radiograph from a neurologically devastated child who presented with respiratory failure, fever, and wheezing. He chronically aspirates his oral secretions, and this episode began with upper respiratory symptoms. An endotracheal tube that is too low has been placed. The patchy infiltrates are most prominent in the bases.
CHEST RADIOGRAPH
Baseline radiographs may show peribronchial thickening, atelectasis, scattered infiltrates, or hyperinflation, or bronchiectasis. Radiographs obtained during acute aspiration pneumonia are more likely to show active disease with segmental or lobar infiltrate, especially in dependent areas of the lung (Fig. 511-1).
HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF THE CHEST
High-resolution computed tomography (HRCT) scanning gives more precise information about lung damage than do plain radiographs (Fig. 511-2). These scans demonstrate the detail of bronchiectasis, “tree-in-bud” opacities, and air trapping more clearly.151-153 Findings may be present before clinical symptoms are present, so obtaining an HRCT should be considered in most children with potential CPA. Serial HRCT can follow progression or resolution of lung damage with time and interventions because it provides more detail.
TREATMENT OF ACUTE SMALL VOLUME ASPIRATION
Aspiration must be treated acutely when symptoms are present. As in large-volume aspirations, small-volume aspirations of gastric material and food, although irritating, are sterile and do not require antibiotics. The children may require supportive care, such as suctioning, oxygen, or bronchodilators, to treat bronchospasm for hours to days after the event. Close monitoring is warranted to ensure a secondary bacterial infection does not occur.
Aspiration of oral contents may, instead, result in aspiration pneumonia from aspiration of pathogenic bacteria from the upper airway. Children with true aspiration pneumonia may have fever, persistent cough, and wheeze in addition to acute respiratory distress. Treatment should be supportive, as described previously, but also should include antibiotics to cover common upper respiratory pathogens (Table 511-3).
FIGURE 511-2. High-resolution computed tomography scans in the same patient in 2002 (top) and 2003. The patient had esophageal atresia at birth treated with colonic interposition. She was a chronic aspirator of refluxed food. Tree-in-bud opacities, bronchial wall thickening, air trapping, and linear densities are all seen and most prominent in the right upper lobe. Bronchiectasis progressed from 2002 to 2003 because the child continued to aspirate.
COMPLICATIONS OF RECURRENT ASPIRATION
The long-term complications of aspiration include chronic disabling symptoms associated with airway inflammation such as chronic cough and wheeze. Recurrent pneumonias, bronchiectasis, and subsequent infection lead to pulmonary fibrosis and scarring with respiratory insufficiency. Potential complications from therapy include inadequate nutritional intake and malnutrition, intolerance to tube feeds, or worsening of GER with subsequent aspiration. Medications and surgeries also have potential complications, so no therapy should be instituted without considering the risks versus the benefits.
OUTCOMES OF RECURRENT ASPIRATION
Outcomes are dependent on the successful, early institution of therapy. If aspiration of food, liquid, and saliva is prevented, the symptoms of airway inflammation and lung damage can also be prevented. Alternatively, when aspiration is allowed to continue, the outcome is usually progressive lung damage, respiratory insufficiency and disability (chronic oxygen dependency), and occasionally death from overwhelming pneumonia.
Table 511-3. Typical Pathogens in Aspiration Pneumonitis
|
Birth–1 year |
|
Streptococcuus salivarius |
|
Staphylococcus species |
|
Neisseria species |
|
Veillonella species |
|
Actinomyces species |
|
Nocardia species |
|
Fusobacterium species |
|
Bacteroides species |
|
Corynebacterium |
|
Candida species |
|
Coliforms |
|
Over 1 year |
|
Fusobacterium species |
|
Bacteroides species |
|
Prevotella species |
|
Peptostreptococci |
|
Escherichia coli |
|
Klebsiella pneumoniae |
|
Staphylococcus aureus |
|
Institutionalized/on antibiotics |
|
Escherichia coli |
|
Proteus species |
|
Pseudomonas aeruginosa |
|
Hospitalized/with abscess |
|
Escherichia coli |
|
Klebsiella pneumonia |
|
Pseudomonas aeruginosa |
|
Yeast |
|
Fungus |