*3.3.2 Bacterial pneumonitis*

*Special Considerations in Human Airway Management*

**3.2 Pathophysiology of pulmonary aspiration**

**3.3 Types of aspiration-related pulmonary complications**

*Summary of pathophysiology of pulmonary aspiration, modified from Dal Santo et al. [8].*

1.Aspiration pneumonitis or chemical pneumonitis

*3.3.1 Aspiration pneumonitis or chemical pneumonitis*

Chemical pneumonitis, the most common type of pulmonary aspiration, was first described by Curtis Lester Mendelson in 1946 as inflammation of the lung parenchyma resulting from aspiration of sterile gastric contents. The morbidity and mortality associated with aspiration pneumonitis can be attributed to the acidity and volume of the aspirate. If the pH of the aspirate is less than 2.5 and the volume is >0.3 ml/kg (20–25 ml in adults), it can lead to fatal

The acidity of the aspirate can cause chemical injury to the tracheobronchial tree and the lung parenchyma which can trigger a series of immune responses. The direct corrosive effect of gastric acid on the alveolar-capillary epithelium peaks in 1–2 h. This is followed by an inflammatory response which peaks in 4–6 h which involves neutrophilic invasion of the alveoli and lung parenchyma. This phase is also characterized by the involvement of a spectrum of inflammatory mediators, inflammatory cells, adhesion molecules, and enzymes, including tumor necrosis factor α, interleukin-8, cyclooxygenase and lipoxygenase products, and reactive

2.Bacterial pneumonia

**Figure 1.**

pneumonitis [9].

3.Particle-associated aspiration

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A contaminated aspirate can lead to bacterial infection of the lung parenchyma, with a course of complete recovery or progress to lung abscess formation, exogenous lipoid pneumonia or chronic interstitial fibrosis. The most common pathogens are *Staphylococcus aureus*, *Pseudomonas aeruginosa*, Enterobacter species, Klebsiella species and *Escherichia coli*. The major anaerobes that have been isolated from pulmonary infections include Pepto streptococcus, Fusobacterium nucleatum, Fusobacterium necrophorum, Prevotella, Bacteroides melaninogenicus [11].
