Using the term “aspiration” without clearly defining the clinical aspiration syndrome you are concerned with

Believing that aspiration pneumonia is solely a disease of swallowing difficulty and food aspiration

Believing that aspiration pneumonia is a disease of gastroesophageal reflux disease

Pursuing drainage of a lung abscess

Treating a drained empyema with prolonged antibiotics (> 14 days)

Failing to treat a lung abscess with prolonged antibiotics until (often > 30 days) radiographic improvement and/or resolution of necrosis

Narrowing antibiotic coverage of an empyema based on the growth of a dominant pathogen (eg, MRSA) when commensurate infection with oral anaerobes is routine (oral anaerobes should always remain covered)

Believing aspiration only occurs in dependent lung zones

Aspiration is defined as the inhalation of anything (besides a gas) past the vocal cords into the lower airway

The reflexes of the oropharynx, glottis, and epiglottis are designed to prevent aspiration; therefore aspiration often occurs at times of central sedation when these reflexes are blunted (eg, sleep, sedation)

There are six major types of aspiration events ( Table 11.1 )

Microaspiration of oral contents occurs nightly in individuals, followed by cough and little else

All typical pneumonias occur when individuals experience a microaspiration event (oral contents) at a time when they are also asymptomatically carrying a pathogenic organism in their oral pharynx (eg, Streptococcus pneumoniae )

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  Often occurs in the setting of impaired host defenses (eg, postviral period, sleep deprivation, stress)

  
  
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  This is unlike many atypical pneumonias , which are inhaled (eg, tuberculosis [TB], legionella, fungal)

Food aspiration occurs in patients with impaired swallowing and leads to food impaction with associated postobstructive pneumonia, lung abscess, and/or empyema

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  Impacted food may have to be mechanically removed via bronchoscopy, in addition to treatment with antibiotics covering oral anaerobes

Gastric aspiration occurs when patients are sedated and experience a large volume emesis of gastric contents/secretions

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  Causes instantaneous chemical injury (pneumonitis) with varying degrees of food-particle impaction, depending on how recently the patient ate

  
  
  
  
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    Bronchoscopy is only useful for removing large particulate matter

    
    
    
    
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      Lavage right after gastric aspiration does not mitigate the instantaneous alveolar chemical injury seen with gastric aspiration

    
    

  
  
  
  
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  may progress to ARDS

  
  
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  To minimize risk, patients are made nil per os (NPO) for several hours before sedation

Gastroesophageal reflux disease with recurrent nocturnal aspiration may lead to basilar fibrotic changes (misconstrued or concerning for pulmonary fibrosis)

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  Gastric aspiration is often clinically silent and may need a pH probe study to confirm

  
  
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  Interventions include acid suppression, elevation of the head of the bed, and promotility agents (ie, metoclopramide)

Spectrum of lung infections caused by macro aspiration of bacteria-rich oral secretions, often occurring during sedated sleep

Causes four distinct clinical/radiographic syndromes (existing on a spectrum)

• 1.
  

  Aspiration pneumonia ( Fig. 11.1 )

  
  
  
  
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    Subacute presentation (eg, days of coughing with low-grade fevers), nontoxic appearing, and an often normal or only slight elevated white blood cell (WBC) count

    
    
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    Chest x-ray film typically shows patchy, basilar, nodular, and round opacities, often with an effusion

    
    
    
    
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      May have small areas of necrosis

    
    
    
    
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    Sputum Gram stain and culture typically show polymorphonuclear leukocytes (PMNs) and “normal oral flora” only (eg, culture negative)

  
  

  
  

  
  

  

  
  

  
  

  Posterioranterior (PA) and lateral chest x-ray films of a patient who was recently started on narcotics because of a wrist fracture and presented with a week of low-grade fevers and productive coughing. The frontal view shows nodular, patchy opacities in the left lower lobe. The lateral film shows a dominant round lesion and a blunted costophrenic angle (CPA) suggesting effusion.

  
  
  
  
• 2.
  

  Lung abscess (cavitary [necrotizing] parenchymal lung lesion with an air-fluid level)

  
  
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  Empyema (complicated parapneumonic effusion)

  
  
  
  
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    Often with air and pus in the pleural space (ie, hydropneumothorax)

    
    
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    May only have small areas of parenchymal consolidation/pneumonia (dominant feature/process is the effusion)

  
  
  
  
• 4.
  

  Accumulation/spillage into areas of preexisting parenchymal abnormality appearing as “pseudonecrosis”

Associated with poor oral hygiene, central sedation (alcohol or sedatives), and sleep

Fever and productive cough are not typical presenting features of lung abscess and empyema

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  Spectrum of chief complaints associated with radiographic presentation ( Fig. 11.2 ):

  
  
  
  
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    Asymptomatic : seen with spillage of oral contents into areas of preexisting parenchymal abnormality

    
    
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    Malaise : weight loss, fatigue, and night sweats are seen with lung abscess

    
    
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    Chest pain : seen with early empyema presentation (as the infection penetrates the pleural cavity)

    
    
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    Shortness of breath : seen with late empyema presentation (as the effusion causes whole lung atelectasis)

  
  

  
  

  
  

  

  
  

  
  

  (A)Chest x-ray obtained for preoperative clearance in an asymptomatic individual. The film suggests a right apical nodular cavitary process. This opacity actually represents a preexisting emphysematous area with superimposed oral aspiration (a.k.a. pseudonecrosis). (B) Chest x-ray with a large, dense, well-circumscribed, round opacity with necrosis evidenced by an air-fluid level (straight line in the cavity) demonstrating the classic appearance of a lung abscess. The patient presented with a chief complaint of weight loss (no pulmonary complaints and normal white blood cell count) and was admitted with the diagnosis of “failure to thrive” before the chest x-ray resulted. (C) Chest x-ray of a patient who presented with sudden onset severe left-sided chest pain (woke him from sleep). He denied cough or fevers. The film shows a patchy left lower lobe consolidation with an effusion; constellation most commonly representing pneumonia and parapneumonic effusion. Chest pain in this scenario (pleural in origin) likely represents pleural spread of infection. (D) Chest x-ray of an individual presenting with shortness of breath, demonstrating a large right-sided hydropneumothorax. This constellation of findings occurring spontaneously (ie, not after a thoracentesis) is seen when both a pleural effusion and a BF fistula are present (the amount of air is too much to be attributed to gas-forming organisms) and is most commonly seen in empyema. The patient required urgent chest tube placement to prevent “tension physiology”

  
  

Clinical radiographic disconnect is common, often with a muted clinical presentation:

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  Imaging looks terrible patient looks good

  
  
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  Normal or slightly elevated WBC count and afebrile

  
  
  
  
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    Late empyema (as in Fig. 11.1 ) typically has abscess-level WBC count (eg, 20,000–30,000)

  
  

Differential diagnosis (things that cause necrotic pulmonary masses):

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  Lung cancer , especially squamous cell carcinoma, given its proclivity for necrosis

  
  
  
  
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    Establishing growth characteristics with previous imaging is invaluable for distinguishing oral anaerobic lung infection (disease of weeks to months) from non-small-cell lung cancer (disease of years) ( Fig. 11.3 )

    
    

    
    

    
    

    

    
    

    
    

    (A) A chest computed tomography (CT) scan with a large left upper lobe lung abscess. A baseline CT scan of the patient’s chest obtained 4 months prior is without abnormality. These growth characteristics are almost incompatible with malignancy. (B) A chest CT scan with a large left lower lobe cavitary mass. A CT scan of the chest 2 years prior shows a spiculated lung nodule. A thick-walled cavity evolving from a spiculated nodule over 2 years represents the natural history of squamous cell carcinoma. Given that lung abscess and lung cancer may have identical clinical radiographic presentations, growth characteristics (if previous imaging is available) are critical.

    
    

  
  
  
  
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  Typical necrotizing pneumonia (eg, staph or aerobic GNR) ( Fig. 11.4 )

  
  
  
  
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    Has classic pneumonia presentation (acute onset fever, high WBC count, and dramatic productive cough), unlike oral anaerobic lung infection

  
  

  
  

  
  

  

  
  

  
  

  Lung cavitation occurring with acute fever, cough, and leukocytosis suggests typical necrotizing bacterial pneumonia and should prompt empiric antibiotic coverage aimed at Staphylococcus and Klebsiella (and other Gram-negative rods [GNRs]). Acute presentations with high fever and dramatic cough are not common with oral anaerobic lung infection.

  
  
  
  
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  Reactivation tuberculosis (TB)

  
  
  
  
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    TB always needs to be considered with cavitary nodular lung disease especially in individuals with sub-acute cough, wt loss and or night sweats

    
    
    
    
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      History (TB exposure/purified protein derivative [PPD]) and imaging (fibronodular opacity in the apical posterior segments) may significantly heighten or lessen the concern for TB

      
      
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      Low threshold for respiratory isolation, sputum examination for acid-fast bacilli (AFB), and quantiferon testing

    
    

  
  
  
  
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  Pseudonecrosis

  
  
  
  
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    Occurs when aspirated oral contents and subsequent anaerobic infected material accumulate in areas of preexisting parenchymal abnormality (eg, emphysema), leading to the appearance of a necrotic pneumonia (ie, a consolidation with lots of holes and small air-fluid levels)

    
    
    
    
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      Actually preexisting emphysematous holes

      
      
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      Typically asymptomatic

    
    
    
    
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    Diagnosis hinges on the presence of old imaging demonstrating that the areas appearing as necrosis on the current film actually represent preexisting holes

    
    
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    Differential diagnosis (DDx): Includes entities that cause asymptomatic, dense consolidations in patients with parenchymal lung disease:

    
    
    
    
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      Chronic necrotizing aspergillosis, reactivation TB, lung cancer, and cryptogenic organizing pneumonia (COP)

    
    
    
    
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    Treatment is he same as it is for lung abscess (ie, oral anaerobic coverage until radiographic resolution)

  
  
  
  
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  c–ANCA vasculitis (rare)

  
  
  
  
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    Associated pathology (eg, sinus disease, glomerulonephritis, mononeuritis multiplex) raises suspicion

  
  
  
  
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  Necrotizing sarcoidosis (rare)

  
  
  
  
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    Multiple lesions, no response to antibiotics