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


#### *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 pneumonitis [9].

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

**107**

**Figure 2.**

*Airway Management in Full Stomach Conditions DOI: http://dx.doi.org/10.5772/intechopen.93591*

neutrophils & complement activation [9].

3.Refractory severe course.

*3.3.3 Particle-associated aspiration*

*3.3.2 Bacterial pneumonitis*

1.Clinical and radiological improvement.

oxygen species, though the major role in the mechanism of lung injury is played by

2.Initial improvement then gradual clinical and radiological deterioration.

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].

mediastinal shift and elevated diaphragm as shown in **Figure 2** below.

*A chest radiograph (on the left) for a patient with a witnessed aspiration of food particles after neurointervention procedure under sedation, showing right upper lobe atelectasis and bilateral pulmonary edema and infiltrates. (On the right), the resolution of collapse and infiltrates after 2 days of respiratory support with invasive ventilation and Tazocin antibiotics in ICU. Picture courtesy of Dr. El Sayed E lKarta with his* 

*permission, Hamad Medical Corporation, Doha, Qatar.*

If particulate matter is present in the aspirate it can lead to variable degrees of airway obstruction. The severity of airway obstruction depends upon the size of the particle and the caliber of the airways. Aspiration of a larger particle can even lead to complete airway obstruction with subsequent sudden respiratory distress, cyanosis, and aphonia that may lead to sudden death if the obstruction is not immediately relieved. Smaller particles in the distal airways cause less severe obstruction and gradual course of respiratory symptoms as irritative cough, wheezing, dyspnea and superimposed bacterial pneumonia if the distal obstruction persists for more than 1 week. Chest X-Ray could show atelectasis or obstructive emphysema with a

The clinical course may have either of the 3 outcomes [10]:

#### *Airway Management in Full Stomach Conditions DOI: http://dx.doi.org/10.5772/intechopen.93591*

oxygen species, though the major role in the mechanism of lung injury is played by neutrophils & complement activation [9].

The clinical course may have either of the 3 outcomes [10]:

