Aspiration is defined as the inhalation of either oropharyngeal or gastric
contents into the lower airways. Inhalation of these contents can lead to
aspiration pneumonia and aspiration pneumonitis. Although these two entities
are managed differently, they are often interchangeably referred to as
aspiration pneumonia.Aspiration pneumonitis represents chemical damage to the
tracheobronchial tree caused by acute, often witnessed, inhalation of
regurgitated gastric contents in patients with an acute change in mental
status. Aspiration pneumonia results from chronic, usually unwitnessed,
inhalation of small amounts of oropharyngeal contents leading to an infectious
process. Aspiration pneumonitis
represents an acute, chemical lung injury resulting from the inhalation of
gastric contents. This disease occurs in people with altered levels of
consciousness resulting from seizures, CVA, CNS mass lesions, drug intoxication
or overdose, and head trauma. The risk of aspiration is indirectly related to
the level of consciousness of the patient (ie, decreasing GCS is related with
increased risk of aspiration). The extent and severity of this disease is
directly related to the volume and acidity of the fluid aspirated. Aspiration
of a massive amount of gastric contents, also know as Mendelson syndrome, can
produce acute respiratory distress within 1 hour. The acidity of gastric
contents results in chemical burns to the tracheobronchial tree involved in the
aspiration. Because of the relative sterility of normal gastric contents,
bacteria do not play an important role in the early stages of the disease. This
does not hold true in patients with gastroparesis or small-bowel obstruction or
in those using antacids (PPI, H2-receptor antagonists). Regardless of the
bacterial load of the inoculum, bacterial superinfection may occur after the
initial chemical injury.Aspiration pneumonia is defined as the development of
an infiltrate in a patient at increased risk of oropharyngeal aspiration. It
occurs when a patient inhales material from the oropharynx that is colonized by
upper airway flora. Initial bacteriologic studies into the causative organisms
revealed the anaerobic species to be the predominant pathogens in
community-acquired aspiration pneumonia. However, subsequent studies revealed
that Streptococcus pneumoniae, Staphylococcus
aureus, Haemophilus influenzae, and Enterobacteriaceae are the most
common organisms. Hospital-acquired aspiration pneumonia, on the other hand, is
often caused by gram-negative organisms including Pseudomonas
aeruginosa, particularly in intubated patients. These studies
demonstrated a limited role of anaerobic pathogens in both the community and
nosocomial variants of the disease.This syndrome most commonly occurs in
individuals with chronically impaired airway defense mechanisms. This includes
gag reflex, coughing, ciliary movement, and immune mechanisms, all of which aid
in removing infectious material from the lower airways. Other risk factors
include poor dentition and poor oral care, which both increase the bacterial
burden of oropharyngeal secretions. Clinicians must thus surmise this diagnosis
when a patient presents with risk factors and radiographic evidence of an infiltrate
suggestive of aspiration pneumonia. The location of the infiltrate on chest
radiograph depends on the position of the patient when the aspiration occurred.