Published on Sep 19, 2022 and last reviewed on Feb 28, 2023 - 6 min read
Aspiration can cause various lung complications. This article illustrates the causes and management of aspiration pneumonitis and pneumonia.
Aspiration pneumonitis and pneumonia are infections of the lung caused by inhaling irritants or toxic substances, usually gastric contents, into the lungs. It can cause lung inflammation (chemical pneumonitis), infection (bacterial pneumonia), or airway obstruction. Drowning may also cause inflammation.
What Are the Risk Factors of Aspiration?
The risk factors include:
Impaired swallowing conditions.
Respiratory devices and procedures during treatment.
Gastrointestinal devices and procedures.
Aspiration pneumonia is caused by bacteria that reside in the oral and nasal pharynx. It can occur in community-based or nosocomial (hospital-acquired). In both community or hospital-acquired, anaerobic alone or in combination with aerobic or microaerophilic organisms are involved in causing infections.
Earlier studies revealed that aspiration pneumonia was referred to as infection caused by less virulent bacteria, oropharyngeal anaerobes, after a large volume aspiration event.
Recently, many common hospital-acquired and community-acquired pneumonia results from small volume aspiration of more virulent pathogens from the oral cavity such as Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae, and gram-negative bacteria.
Aspiration pneumonia most commonly occurs in patients with impaired airway mechanisms, such as gag reflex, ciliary movement, coughing, and immune mechanisms.
There are three types of aspiration syndrome classified based on the frequency of aspiration, quantity and nature of aspirated material, and the host factors that predispose to aspiration. These include:
Aspiration of Bacteria- From the oropharyngeal area causes aspiration pneumonia.
Aspiration of Oil- Causes exogenous lipoid pneumonia.
Aspiration of Foreign Bodies- Causes acute respiratory emergencies and may cause bacterial pneumonia.
What Is Acute Aspiration Pneumonia?
Acute aspiration pneumonia occurs when ingested particles, either solid or liquid, accidentally get into the airways and lungs, resulting in inflammation. The body’s normal defense mechanisms (sneezing and coughing) can clear out these tiny particles before getting ingested into the lungs. Due to impaired defense mechanisms or larger aspirated particles, aspiration pneumonia may develop.
The risk factors of acute aspiration pneumonia include-
Loss of consciousness.
Laparoscopic gastric banding.
Structural abnormalities of pharynx and esophagus.
In elderly people.
The risk of aspiration is indirectly proportional to the level of consciousness of the patient (decreased Glasgow coma scale is related to an increased risk of aspiration). In anaerobic bacterial pneumonia, the pathogenesis is related to a large volume of aspirated anaerobes and to host factors that suppress cough, phagocytic efficiency, and mucociliary clearance.
Chemical pneumonitis is also called aspiration pneumonitis or Mendelson syndrome. It is due to the parenchymal inflammatory reaction caused by aspirating large volumes of gastric contents independent of infection.
Various substances are directly toxic to the lungs or stimulate an inflammatory response when aspirated; gastric acid is one of the most common aspirated chemical substances.
If the pH of the aspirated fluid is less than 2.5 and the volume is greater than 0.3 mL per kilogram (KG) of body weight, then it is more likely to cause chemical pneumonitis.
The acidity of gastric contents results in chemical burns to the tracheobronchial tree involved in the aspiration.
After the onset of the initial chemical burn, it is followed by an inflammatory cellular reaction induced by the release of tumor necrosis factor (TNF) - alpha and interleukin (IL - 8).
Other substances include petroleum products (such as petroleum jelly) or laxative oils (paraffin and castor oils). Gasoline and kerosene, when aspirated, also cause chemical pneumonitis.
Among gastric contents such as gastric acid, food, and other ingested materials, gastric acid is more injurious in quantity. Gastric acid irritates and causes a chemical burn of the airways and lungs which results in alveolar hemorrhage, edema, atelectasis (partial or complete collapse of the lung), and bronchoconstriction (narrowing of airways). This condition may resolve spontaneously or may progress to acute respiratory distress syndrome (a condition in which the fluid collects in the air sacs of the lungs).
Aspiration may be presented with symptoms or without any symptoms. The clinical and radiographic features depend on the aspirated volume, pH, and duration. The most common symptoms are:
Cough - that produces sputum (thick or discolored mucus).
Fever or hypothermia.
Shortness of breath (dyspnea).
Decreased breath sounds.
Dullness to percussion.
Egophony (auscultatory finding due to change in the quality of the voice).
Pleural friction rub.
Hypoxemia (low levels of oxygen).
Hypotension (particularly in septic shock cases).
Altered mental status.
Patients with chemical pneumonitis develop acute onset or abrupt development of symptoms within a few minutes to two hours of aspiration event.
Cough with frothy pink sputum.
Tachypnea (increased or rapid breathing).
Tachycardia (increased heart rate).
Rales - Clicking, rattling, bubbling sound in the lungs.
The onset of illness may be subacute or insidious.
Pleuritic chest pain.
Putrid expectoration (foul-smelling sputum).
Fever or chills.
Cough with purulent sputum.
Rigors may be present or absent.
Arterial Blood Gas and Mixed Venous Gas Analysis:
It is used to access oxygenation and pH status. The results evaluate acute hypoxemia in patients with chemical pneumonitis and normal to the low partial pressure of carbon dioxide. A lactate level is used as an early identifier of sepsis or septic shock.
The mixed venous gas measurement indicates septic shock. Decreased mixed venous oxygen saturation is used as a marker for septic shock.
Basic Metabolic Panel:
Serum electrolyte, creatinine levels, and blood urea nitrogen (BUN) levels are used to assess fluid status in significant fluid loss patients presenting with fever, vomiting, or diarrhea. In addition, serum blood urea nitrogen and creatinine levels are used to assess renal function in septic shock patients.
Complete Blood Cell Count With Differential:
An elevated white blood cell count and increased neutrophils are present in patients with chemical pneumonitis. The complete blood cell count demonstrates elevated white blood cell count, increased neutrophils, and thrombocytosis in patients with bacterial pneumonia.
It is used as a baseline screening of bacteremia. In uncomplicated pneumonia, the yield is low and is not necessary for initial management.
It depended on the position of the patient when the aspiration occurred. Patients who aspirate while standing have bilateral lower lung lobe infiltrates. Patients lying in the left lateral decubitus position have left-sided infiltrates. The right upper lobe is involved in the alcoholics who aspirate in the prone position.
It is indicated in patients with chemical pneumonitis only when aspiration of a foreign body or food material is suspected. This is useful in ruling out the presence of an obstructing neoplasm in anaerobic bacterial pneumonia with lung abscess. However, it is not useful in cases of community-acquired aspiration pneumonia.
It is a diagnostic and therapeutic procedure in which fluid or air is removed from between the visceral and parietal pleura. Analysis can determine the underlying cause of the pleural effusion and relief of symptoms.
Antibiotics are recommended for aspiration pneumonia in the following conditions:
If pneumonia fails to resolve within 48 hours.
In patients with small bowel obstruction.
Patients on antacids due to the possibility of gastric colonization with microorganisms.
Ceftriaxone with Azithromycin, Moxifloxacin, and Levofloxacin is recommended.
Telavancin is indicated for hospital-acquired pneumonia.
Piperacillin, Tazobactam or Imipenem, and Cilastatin plus vancomycin are recommended for patients with a toxic appearance or community-acquired pneumonia.
Ceftaroline is used as an alternative to vancomycin for the treatment of community-acquired pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA).
For chemical pneumonitis patients, maintenance of airways, clearance of secretions with tracheal suctioning, oxygen supplementation, and mechanical ventilation, if necessary. If the patient is unable to maintain adequate oxygenation, positive end-expiratory pressure should be considered.
Based on the complications, underlying disease, and the patient's health status, the prognosis of chemical pneumonitis and bacterial aspiration pneumonia can be determined. Patients recovered from chemical pneumonitis generally do not require additional care, except in measures to prevent further aspiration episodes. Proper diagnosis and timely management can help in alleviating the cause and severity of the illness.
Last reviewed at:
28 Feb 2023 - 6 min read
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