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Pneumonia, Aspiration
Article Last Updated: Sep 29, 2006
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Anita B Varkey, MD, Consulting Staff, Division of General Medicine and Primary Care, John H Stroger Jr Hospital of Cook County; Assistant Professor, Department of Medicine, Rush Medical College
Anita B Varkey is a member of the following medical societies: American College of Physicians and Society of General Internal Medicine
Coauthor(s):
Basil Varkey, MD, FCCP, Professor, Department of Internal Medicine, Division of Pulmonary and Critical Care, Froedtert Memorial Lutheran Hospital, Medical College of Wisconsin
Editors: Laurie Robin Grier, MD, Medical Director of MICU, Associate Professor of Medicine, Section of Pulmonary and Critical Care Medicine, Louisiana State University Health Science Center at Shreveport; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Robert S Crausman, MD, MMS, Chief Administrative Officer, Rhode Island Board of Medical Licensure and Discipline, Rhode Island Department of Health; Associate Professor, Department of Medicine, Brown University School of Medicine; Timothy D Rice, MD, Associate Professor, Departments of Internal Medicine and Pediatrics and Adolescent Medicine, Saint Louis University School of Medicine; Zab Mosenifar, MD, Director, Division of Pulmonary and Critical Care Medicine, Director, Women's Guild Pulmonary Disease Institute, Executive Vice Chair, Department of Medicine, Cedars Sinai Medical Center; Professor of Medicine, David Geffen School of Medicine at UCLA
Author and Editor Disclosure
Synonyms and related keywords:
aspiration pneumonia, Mendelson syndrome, chemical pneumonitis, anaerobic bacterial pneumonia, chemical pneumonia, CP, aspiration of gastric acid, bacterial pneumonia, BP, aspiration of bacteria from oral and pharyngeal areas, exogenous lipoid pneumonia, aspiration of oil, aspiration of a foreign body, acute respiratory emergency, parenchymal inflammatory reaction, community-acquired pneumonia, CAP, nosocomial pneumonia, acute respiratory distress syndrome, ARDS
Background
Aspiration, ie, the act of taking foreign material into the lungs, 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. Three types of material cause 3 different pneumonic syndromes. Aspiration of gastric acid causes chemical pneumonia (CP). Aspiration of bacteria from oral and pharyngeal areas causes bacterial pneumonia (BP). Aspiration of oil, eg, mineral oil or vegetable oil, causes exogenous lipoid pneumonia, a rare form of pneumonia. In addition, aspiration of a foreign body may cause an acute respiratory emergency and, in some cases, may predispose the patient to bacterial pneumonia.
Aspiration pneumonia, according to common usage, includes both CP and BP, although the pathophysiology, clinical presentation, treatment, and complications of CP and BP are different.
Pathophysiology
Aspiration, particularly during sleep, is a common event in healthy individuals. No disease ensues 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 3 important determinants of aspiration pneumonia.
CP, also known as Mendelson syndrome, is due to the parenchymal inflammatory reaction caused by a large volume of gastric contents independent of infection. 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 CP. The initial chemical burn is followed by an inflammatory cellular reaction fueled by the release of potent cytokines, particularly tumor necrosis factor–alpha and interleukin-8.
BP caused by aspiration can occur in the community or in the hospital (ie, nosocomial). In both situations anaerobic organisms alone or in combination with aerobic and/or microaerophilic organisms play an important role. Nosocomial BP caused by aspiration is common, and the major pathogens involved are hospital-acquired flora through oropharyngeal colonization (eg, enteric gram-negative bacteria, staphylococci).
In anaerobic pneumonia, the pathogenesis is related to the large volume of aspirated anaerobes (eg, as in persons with periodontal disease) and to host factors (eg, as in alcoholism) that suppress cough, mucociliary clearance, and phagocytic efficiency. 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.
Frequency
United States
A reliable estimate of incidence of CP is not available. BP caused by aspiration is reported to cause 5-15% of community-acquired pneumonia (CAP) cases. Nosocomial BP is the second most likely cause of nosocomial infections, second only to urinary tract infection, and is the leading cause of death from hospital-acquired infections.
Mortality/Morbidity
In Mendelson's original series in 1946, Mendelson described 61 obstetric patients who aspirated gastric acid during anesthesia, all of whom had a complete clinical recovery within 24-36 hours. In subsequent studies, which have included older sicker patients, CP has a reported mortality rate of 30-62% because CP often leads to acute respiratory distress syndrome (ARDS).
- If BP is not treated early, it can lead to development of complications, including lung abscess and bronchopleural fistula.
- Nosocomial pneumonia is associated with a longer period of hospitalization and increased mortality rates.
Age
Nosocomial BP caused by aspiration is much more frequent in adults than in children. Predisposing factors (see Causes) are more common among elderly people; therefore, this population is more prone to develop aspiration pneumonia.
History
- Chemical pneumonitis
- Acute onset
- Abrupt development of symptoms within a few minutes to 2 hours of the aspiration event
- Respiratory distress and rapid breathing
- Audible wheezing
- Cough with pink or frothy sputum
- Bacterial pneumonia
- Subacute or insidious onset: Symptoms occur in a matter of days when aerobic organisms are the pathogens and in days to weeks when anaerobic organisms are the pathogens.
- Cough with purulent sputum
- Absence of rigors
- Putrid odor of sputum (a clue to anaerobic bacterial pneumonia)
- Weight loss
Physical
- Chemical pneumonia
- Tachypnea
- Tachycardia
- Fever
- Rales
- Wheezing
- Cyanosis (possibly)
- Bacterial pneumonia
- Periodontal disease (primarily noted as gingivitis)
- Bad breath
- Clubbing of fingers (possibly)
- Fever
- Bronchial breath sounds and rales over a consolidated posterior area
Causes
Almost all patients who develop aspiration pneumonia have one or more of the predisposing conditions listed below. While all the listed conditions predispose the patient to chemical pneumonia (CP), conditions that alter consciousness and periodontal disease specifically predispose the patient to bacterial pneumonia (BP).
- Conditions associated with altered or reduced consciousness
- Alcoholism
- Drug overdose
- Seizures
- Stroke
- Head trauma
- General anesthesia
- Esophageal conditions
- Dysphagia
- Esophageal strictures
- Esophageal neoplasm
- Esophageal diverticula
- Tracheoesophageal fistula
- Gastroesophageal reflux disease
- Neurologic disorders
- Multiple sclerosis
- Dementia
- Parkinson disease
- Myasthenia gravis
- Pseudobulbar palsy
- Mechanical conditions
- Nasogastric tube
- Endotracheal intubation
- Tracheostomy
- Upper gastrointestinal endoscopy
- Bronchoscopy
- Gastrostomy or postpyloric feeding tubes
- Other types of conditions
- Protracted vomiting
- Prolonged recumbency
- General deconditioning and debility
- Critical illness
Acute Respiratory Distress Syndrome
Lung Abscess
Tuberculosis
Other Problems to be Considered
Necrotizing pneumonia
Bronchopleural fistula
Lung carcinoma
Mycoses
Lab Studies
- Arterial blood gas demonstrates acute hypoxemia in patients with chemical pneumonia (CP) and normal-to-low partial pressure of carbon dioxide with respiratory alkalosis.
- CBC count may reveal an elevated WBC count, increased neutrophils, anemia, and thrombocytosis in patients with bacterial pneumonia (BP) caused by anaerobic bacteria.
- Elevated WBC count and increased neutrophils may be present in patients with CP.
- Sputum Gram stain and microscopy reveal a multitude of bacteria (eg, cocci, bacilli, coccobacillary forms, spirochetes, fusiforms) in patients with BP caused by anaerobic bacteria. Findings on sputum culture may not isolate organisms because the major pathogens are anaerobes.
- In nosocomial BP, sputum culture may be helpful in detecting gram-negative bacteria.
Imaging Studies
- Chest radiographic findings in patients with CP are characterized by the presence of infiltrates, predominantly the alveolar type, in one or both lower lobes or diffuse simulation of the appearance of pulmonary edema. Volume loss in any lobar area suggests obstruction (eg, by aspirated food particles or other foreign bodies) in the bronchus.
- Chest radiographic findings in patients with anaerobic BP typically demonstrate an infiltrate with or without cavitation in one of the dependent segments of the lungs (ie, posterior segments of the upper lobes, superior segments of the lower lobes). Lucency within the infiltrate suggests a necrotizing pneumonia. Air-fluid level within a circumscribed infiltrate (density) indicates a lung abscess or a bronchopleural fistula. Costophrenic angle blunting and the presence of a meniscus are signs of a para-pneumonic pleural effusion.
- Ultrasonography is helpful when confirming and locating pleural effusion.
- CT scan of the chest is not needed in all cases. CT scan is helpful in detecting necrosis within infiltrates, cavities, and loculated pleural effusions. CT scan provides a better definition of the affected areas and is used to differentiate pulmonary abnormalities from pleural abnormalities.
Procedures
- Bronchoscopy is indicated in patients with CP only when aspiration of a foreign body or food material is suspected.
- Transtracheal aspiration (TTA) is useful in obtaining a sputum specimen for anaerobic culture because it bypasses the mouth flora. However, this procedure has now been supplanted by bronchoscopy and use of a protected catheter to retrieve pathogens in BP.
- Bronchoscopy is useful when ruling out the presence of an obstructing neoplasm in anaerobic BP with lung abscess.
- Pulmonary artery catheter placement may be needed to differentiate cardiac from noncardiac pulmonary edema caused by CP and for appropriate fluid management.
- Mechanical ventilation is needed in severe cases of CP that cause ARDS.
Medical Care
- Chemical pneumonia: Treatment should include maintenance of airways and clearance of secretions with tracheal suctioning, oxygen supplementation, mechanical ventilation if the patient is unable to maintain adequate oxygenation, early use of positive end-expiratory pressure (PEEP), and administration of intravenous fluids. Routine use of corticosteroids is not indicated. Early prophylactic use of antibiotics is controversial because no evidence indicates that bacterial infection plays a role in the initial events. Bacterial pneumonia (BP) that may occur later (eg, days after the aspiration event) as a complication of chemical pneumonia (CP) should be treated with appropriate antibiotics.
- Bacterial pneumonia: Antibiotics are the mainstay of treatment. The choice of antibiotics and duration of treatment depend on the suspected or proven causative organisms. Most commonly in community-acquired BP, the causative organisms are indigenous oral flora. These are predominantly anaerobes (eg, Bacteroides species, Fusobacterium species, Peptostreptococcus species) and streptococci. In nosocomial BP (ie, aspiration in the hospital), in addition to the usual oral flora pathogens such as Staphylococcus aureus, Escherichia coli, Klebsiella species, Enterobacter species, and Pseudomonas species may be involved.
Surgical Care
No role for surgical care exists, except in cases with complications.
Consultations
- Pulmonologist - For bronchoscopy when obstruction is suspected in patients with CP or in ruling out a neoplasm in BP cases
- Intensivist (critical care) - For severe CP if hypoxemia is severe and ventilatory support is anticipated
- Thoracic surgeon - For anaerobic BP with complications, eg, closed tube drainage of an empyema, open tube drainage, and decortication
Diet
In patients with stroke or other risk factors for aspiration, a comprehensive swallowing evaluation is recommended. A speech and language therapist can perform this bedside evaluation and, if abnormalities are found, can teach the patient compensatory strategies with soft or pureed foods.
Antibiotics are usually not necessary unless an infection develops.
Chemical pneumonia
Antibiotics are not routinely indicated for patients with CP. If pneumonia occurs days after the aspiration event, antibiotics are indicated. As noted earlier, various organisms are causative. Therefore, choosing antibiotics based on organisms cultured from sputum, tracheal aspirates, or aspirate obtained through a protected catheter by bronchoscopy rather than empirically is more appropriate. The choice of antibiotics is also dictated by the severity of the pneumonia, patient-related risk factors (eg, malnutrition, comorbid illnesses) and intervention-related factors (eg, prior use of antibiotics, corticosteroids, cytotoxic agents, endotracheal tube), and the duration of hospitalization.
As examples, dual treatment involving a carefully chosen second-generation cephalosporin or nonpseudomonal third-generation cephalosporin and clindamycin, aztreonam, or fluoroquinolones is appropriate in many cases. However, in severe pneumonia occurring many days after initiation of mechanical ventilation, the probability of resistant organisms, including Pseudomonas aeruginosa, Acinetobacter species, and methicillin-resistant S aureus is increased, and, therefore, antibiotic treatment should be broader and aggressive; the choices include ciprofloxacin, quinolones, aminoglycoside with antipseudomonal penicillin, ceftazidime, imipenem, and vancomycin.
Bacterial pneumonia
In BP, clindamycin is the antibiotic of choice. Alternatives to clindamycin include amoxicillin with clavulanate (Augmentin) and metronidazole (Flagyl). Metronidazole used alone is not recommended because of a high failure rate. Similarly, macrolides, cephalosporins, and fluoroquinolones are additional alternatives that are not recommended as first-line agents because they are not well studied.
Drug Category: Antibiotics
Antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.
| Drug Name | Clindamycin (Cleocin) |
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| Description | Available in parenteral form (ie, clindamycin phosphate) and oral form (ie, clindamycin hydrochloride). Oral clindamycin is absorbed rapidly and almost completely and is not appreciably altered by the presence of food in the stomach. Appropriate serum levels are reached and sustained for at least 6 h following an oral dose. No significant levels are attained in the cerebrospinal fluid. Also effective against aerobic and anaerobic streptococci (except enterococci). Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. |
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| Adult Dose | 600 mg IV q8h; continue treatment with 300 mg PO q6h; doses as high as 4800 mg qd have been used in life-threatening severe infections |
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| Pediatric Dose | 8-20 mg/kg/d PO as hydrochloride and 8-25 mg/kg/d as palmitate divided tid/qid
20-40 mg/kg/d IV/IM equally divided tid/qid
Use the higher dose for more severe infections |
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| Contraindications | Documented hypersensitivity; regional enteritis, ulcerative colitis, pseudomembranous colitis; hepatic impairment |
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| Interactions | Increases duration of neuromuscular blockade induced by tubocurarine and pancuronium; erythromycin may antagonize effects of clindamycin; antidiarrheals may delay absorption of clindamycin |
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| Pregnancy | B - Usually safe but benefits must outweigh the risks.
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| Precautions | Adjust dose in severe hepatic dysfunction; no adjustment is necessary in renal insufficiency; associated with severe and possibly fatal colitis; if diarrhea develops during the course of treatment, clindamycin should be stopped |
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| Drug Name | Amoxicillin/clavulanate potassium (Augmentin) |
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| Description | Combines a semisynthetic antibiotic (ie, amoxicillin) and a beta-lactamase inhibitor (ie, clavulanate potassium) and provides for an extended spectrum of coverage to include bacteria resistant to amoxicillin and other beta-lactam antibiotics. It is well absorbed from the gastrointestinal tract and can be administered without regard to the time of a meal. The half-life of oral Augmentin is 1-1.3 h. Augmentin has good tissue penetration but does not enter the cerebrospinal fluid. Drug combination treats bacteria resistant to beta-lactam antibiotics. |
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| Adult Dose | 500 mg q12h PO or 875 mg PO q12h in severe infections |
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| Pediatric Dose | <3 months: Not established
>3 months: Base dosing protocol on amoxicillin content
<40 kilograms: 20-40 mg/kg/d PO divided bid; do not use 250-mg tab until child weighs >40 kg
>40 kilograms: Administer as in adults |
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| Contraindications | Documented hypersensitivity |
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| Interactions | Probenecid decreases renal tubular secretion and may result in prolonged and high level of amoxicillin; concurrent use of allopurinol substantially increases incidence of skin rashes; coadministration with warfarin or heparin increases risk of bleeding |
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| Pregnancy | B - Usually safe but benefits must outweigh the risks.
|
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| Precautions | May cause antibiotic-associated diarrhea and because this is associated with pseudomembranous colitis, stop administration of the drug if diarrhea occurs; hepatic dysfunction manifested by rise in liver enzymes may occur; increased incidence of erythematous skin rash in patients with infectious mononucleosis who are administered ampicillin |
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Further Inpatient Care
- Patients with aspiration pneumonia, both chemical pneumonia (CP) and bacterial pneumonia (BP), need inpatient care for several reasons, including the acuity of illness, host factors, and the uncertain course and prognosis of aspiration pneumonia.
Further Outpatient Care
- Patients who recover from CP generally do not require additional outpatient care, except for adherence to measures to prevent further aspiration episodes.
- Because anaerobic bacterial infections require prolonged antibiotic treatment, outpatient treatment is necessary. Patients can be discharged from the hospital after clinical improvement and stability (eg, no fever, no leucocytosis, resolution of hypoxemia) and radiographic improvement (eg, decreased infiltrate or cavity size, no pleural effusion).
In/Out Patient Meds
- Oral antibiotic therapy (ie, clindamycin) is continued for several weeks. In treating a lung abscess, 6-8 weeks of daily antibiotic therapy may be required until the cavity has disappeared or diminished in size and has remained stable for more than 1 week.
Deterrence/Prevention
- Position patients with altered consciousness in a semirecumbent position with the head of the bed at a 30- to 45-degree angle. Use nonparticulate antacids and histamine 2 (H2) blockers to reduce gastric acidity. Use antiemetics to reduce lower esophageal sphincter pressure. Before starting enteral tube feeding, confirm the tip location radiographically. Check residual gastric volume regularly. For those on bolus tube, feeding residual should not exceed 150 mL before the next bolus feed.
- For patients with known swallowing dysfunction, helpful compensatory techniques to reduce aspiration include a soft diet reducing the bite size, keeping the chin tucked and the head turned, and repeated swallowing.
Complications
- Complications of CP
- Complications of BP
- Para-pneumonic effusion
- Empyema
- Lung abscess
- Bronchopleural fistula
Prognosis
- The prognosis of both CP and BP is dependent on underlying diseases, complications, and host status.
Patient Education
Medical/Legal Pitfalls
- Not recognizing or not weighing the risk for aspiration based on predisposing conditions
- Feeding patients at high risk for aspiration
- Resumption of feeding after intubation without assessing patient's ability to swallow and gastric motility
- Delay in diagnosis of anaerobic lung abscess because of subacute presentation
- Misdiagnosis of anaerobic lung abscess (mistaken for lung carcinoma or tuberculosis)
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Pneumonia, Aspiration excerpt Article Last Updated: Sep 29, 2006
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