Aspiration Syndromes
John L. Colombo
Aspiration Syndromes
Aspiration of material that is foreign to the lower airway produces a varied clinical spectrum ranging from an asymptomatic condition to acute life-threatening events, such as occur with massive aspiration of gastric contents or hydrocarbon products. Other chapters discuss mechanical obstruction of large- or intermediate-size airways as occurs with foreign bodies (see Chapter 414 ) and infectious complications of aspiration and recurrent microaspiration (see Chapter 426 ), such as may occur with gastroesophageal reflux (see Chapter 349.1 ) or dysphagia (see Chapter 332 ). Occult aspiration of nasopharyngeal secretions into the lower respiratory tract is a normal event in healthy people, usually without apparent clinical significance.
Gastric Contents
Aspiration of substantial amounts of gastric contents typically occurs in the context of vomiting. It is an infrequent complication of general anesthesia, gastroenteritis, or altered level of consciousness. Among 63,180 pediatric patients undergoing general anesthesia, 24 cases of aspiration occurred, but symptoms developed in only 9. Pathophysiologic consequences can vary, depending primarily on the pH and volume of the aspirate and the amount of particulate material. Increased clinical severity is noted with volumes greater than approximately 0.8 mL/kg and/or pH < 2.5. Hypoxemia, hemorrhagic pneumonitis, atelectasis, intravascular fluid shifts, and pulmonary edema all occur rapidly after massive aspiration. These occur earlier, become more severe, and last longer with acid aspiration. Most clinical changes are present within minutes to 1-2 hr after the aspiration event. In the next 24-48 hr, there is a marked increase in lung parenchymal neutrophil infiltrations, mucosal sloughing, and alveolar consolidation that often correlates with increasing infiltrates on chest radiographs. These changes tend to occur significantly later and are more prolonged after aspiration of particulate material. Although infection usually does not have a role in initial lung injury after aspiration of gastric contents, aspiration may impair pulmonary defenses, predisposing the patient to secondary bacterial pneumonia. In the patient who has shown clinical improvement but then demonstrates clinical worsening, especially with fever and leukocytosis, secondary bacterial pneumonia should be suspected.
Treatment
If large-volume or highly toxic substance aspiration occurs in a patient who already has an artificial airway in place, it is important to perform immediate suctioning of the airway. If immediate suctioning cannot be performed, later suctioning or bronchoscopy is usually of limited therapeutic value except when there is suspicion of significant particulate aspiration. Attempts at acid neutralization are not warranted because acid is rapidly neutralized by the respiratory epithelium. Patients in whom large-volume or toxic aspiration is suspected should be observed, should undergo oxygenation measurement by oximetry or blood gas analysis, and should undergo a chest radiograph, even if they are asymptomatic. If the chest radiograph findings and oxygen saturation are normal, and the patient remains asymptomatic, home observation, after a period of observation in the hospital or office, is adequate. No treatment is indicated at that time, but the caregivers should be instructed to bring the child back in for medical attention should respiratory symptoms or fever develop. For patients who present with abnormal findings or in whom such findings develop during observation, oxygen therapy is given to correct hypoxemia. Endotracheal intubation and mechanical ventilation are often necessary for more severe cases. Bronchodilators may be tried, although they are usually of limited benefit. Animal studies indicate that treatment with corticosteroids does not provide benefit, unless given nearly simultaneously with the aspiration event; use of these agents may increase the risk of secondary infection. Prophylactic antibiotics are not indicated, although in the patient with limited reserve, early antibiotic coverage may be appropriate. If used, antibiotics that cover for anaerobic microbes should be considered. If the aspiration event occurs in a hospitalized or chronically ill patient, coverage of Pseudomonas , Staphylococcus aureus, and enteric Gram-negative organisms should also be considered. Various antibiotic choices have included clindamycin plus ampicillin-sulbactam or a carbapenem or a respiratory fluoroquinolone. If empiric antibiotics are given, they should be discontinued when cultures and course warrant. A mortality rate of ≤ 5% is seen if 3 or fewer lobes are involved. Unless complications develop, such as infection or barotrauma, most patients recover in 2-3 wk. Prolonged lung damage may persist, including scarring, bronchiolitis obliterans, and bronchiectasis.
Prevention
Prevention of aspiration should always be the goal when airway manipulation is necessary for intubation or other invasive procedures. Feeding with enteral tubes passed beyond the pylorus, elevating the head of the bed 30-45 degrees in mechanically ventilated patients, and oral decontamination reduce the incidence of aspiration complications in the intensive care unit. Minimizing use of sedation, monitoring for gastric residuals, and gastric acid suppression may all help prevent aspiration. However, the latter is not without some controversy. Any patient with altered consciousness, especially one who is receiving tube feedings, should be considered at high risk for aspiration. Preoperative restriction of oral fluids to otherwise normal children for 6 hr does not appear to provide benefit compared to restriction for only 2 hr in terms of risk for aspiration.
Hydrocarbon Aspiration
Aspiration and resulting pneumonitis are typically the most dangerous consequences of acute hydrocarbon ingestion (see Chapter 77 ). Although significant pneumonitis occurs in <2% of all hydrocarbon ingestions, an estimated 20 deaths occur annually from hydrocarbon aspiration in both children and adults. Some of these deaths represent suicides. Hydrocarbons with lower surface tensions (gasoline, turpentine, naphthalene) have more potential for aspiration toxicity than heavier mineral or fuel oils. Ingestion of >30 mL (approximate volume of an adult swallow) of hydrocarbon is associated with an increased risk of severe pneumonitis. Clinical findings including chest retractions, grunting, cough, and fever may occur as soon as 30 min after aspiration or may be delayed for several hours. Lung radiographic changes usually occur within 2-8 hr, peaking in 48-72 hr (Fig. 425.1 ). Pneumatoceles and pleural effusions may occur. Patients initially presenting with cough, shortness of breath, or hypoxemia are at high risk for pneumonitis. Persistent pulmonary function abnormalities can be present many years after hydrocarbon aspiration. Other organ systems, especially the liver, central nervous system, and heart, may suffer serious injury. Cardiac dysrhythmias may occur and may be exacerbated by hypoxia and acid–base or electrolyte disturbances.
Treatment
Gastric emptying is contraindicated in nearly all situations because the risk of aspiration is greater than any systemic toxicity. Treatment is generally supportive, consisting of oxygen, fluids, and ventilatory support, and rarely extracorporeal membrane oxygenation, as necessary. Exogenous surfactant administration has been described as helpful in case reports. The child who has no symptoms and normal chest radiograph findings should be observed for 6-8 hr to ensure safe discharge.
Certain hydrocarbons have more inherent systemic toxicity . The mnemonic CHAMP refers collectively to the following hydrocarbons: c amphor, h alogenated carbons, a romatic hydrocarbons, and those associated with m etals and p esticides. Patients who ingest these compounds in volumes > 30 mL, such as might occur with intentional overdose, may benefit from gastric emptying. This is still a high-risk procedure that can result in further aspiration. If a cuffed endotracheal tube can be placed without inducing vomiting, this procedure should be considered, especially in the presence of altered mental status. Treatment of each case should be considered individually, with guidance from a poison control center.
Other substances that are particularly toxic and cause significant lung injury when aspirated or inhaled include baby powder, chlorine, shellac, beryllium, and mercury vapors. Repeated exposure to low concentrations of these agents can lead to chronic lung disease, such as interstitial pneumonitis and granuloma formation. Corticosteroids may help reduce fibrosis development and improve pulmonary function, although the evidence for this benefit is limited.