Aspiration Pneumonia and Pneumonitis

Definition

Aspiration pneumonia is a condition where foreign material enters the lower airways thereby causing inflammation of the lung. It can result in chemical damage of the lung tissue or a lung infection. The term aspiration pneumonia is usually reserved for a lung infection, mainly bacterial, where the bacteria carried into the lung is through aspirated material.

Aspiration pneumonitis, or chemical pneumonitis, is the term for chemical injury and inflammation of the lung tissue without an infection. However, an infection may set in days later. The term aspiration pneumonia is broadly used for both chemical injury and infection of the lung tissue. The condition can lead to complications such as a lung abscess, acute respiratory distress, pulmonary fibrosis and even death.

Incidence

Pneumonia is not an uncommon lung condition. It is often associated with viral and bacterial infections. However, recent studies have revealed that a significant number of cases of bacterial pneumonia is a consequence of aspiration. The prevalence is substantially higher in hospitalized patients (nosocomial), especially those on a ventilator, who are in a coma or have neurological conditions.

Pathophysiology

The airways are lined with respiratory epithelium that is specialized for its function. It ensures that air entering the lungs is filtered out of dust and microbes. These particles are trapped within the mucus secreted by the respiratory epithelium and tiny hair-like projections known as cilia push the mucus out of the airways. When there is a high concentration of irritants in the airway, pulmonary irritant receptors in the airway lining elicits the cough reflex which quickly pushes out any foreign material. In this manner the airway is quickly flushed out.

Contents within the mouth, throat and nose usually pass down into the esophagus (food pipe) and then into the stomach if it is not expelled into the environment. This includes substances that are inhaled, ingested or the natural secretions within the mouth and nose. Sometimes, however, these substances and secretions “leak” into the airways. Similarly, the stomach contents (digestive enzymes + acid + partially digested food) may also rise up in the esophagus and enter the airways. It can eventually “drip” into the lower airways and reach the lungs.

As stated, the cough reflex is meant to protect the airways and lungs from the entry of these foreign material. In some people this cough reflex is impaired and the foreign material is able to enter the furthest parts of the bronchial tree to reach the lung tissue. It may cause direct chemical irritation or may carry microbes deep into the lungs where an infection sets in. Broadly this condition is referred to as aspiration pneumonia but this term does not clearly identify whether an infection is present or not and the mechanism of the lung injury.

Types

Broadly aspiration pneumonia is seen in three forms due to three different types of foreign material.

  1. Bacterial pneumonia when bacteria in the foreign material is able to enter the lungs and establish an infection.
  2. Chemical pneumonitis where toxic substances, like stomach acid, enters the airways and damages the lung tissue.
  3. Exogenous lipoid pneumonia where mineral or vegetable oils.

Symptoms

Generalized respiratory symptoms may be present to varying degrees in aspiration pneumonia.

  • Productive cough
  • Shortness of breath
  • Fever (sometimes)
  • Chest pain

Patients with aspiration pneumonia may also exhibit with the following signs :

  • Rapid breathing (tachypnea)
  • Rapid heart rate (tachycardia)
  • Abnormal breathing soundsĀ  (rales, wheezing, whispering pectroriloquy and bronchial breathing)
  • Low body temperature (hypothermia) if fever is not present.
  • Pink-colored to red sputum (hemoptysis)
  • Bluish tinge of the lips, fingers and/or toes (cyanosis)

Causes

Aspiration pneumonia is unlikely to arise in a healthy person who is conscious and has properly functioning gag and cough reflexes. In most instances, aspiration pneumonia is seen as a complication of some underlying conditions where normal airway clearance is compromised.

In chemical pneumonitis, the entry of gastric acid into the airways and finally to the lung tissue causes severe chemical burns. If a large volume of gastric acid reaches the lungs, it can cause extensive damage and even lead to acute respiratory distress within a short period of time, sometimes within hours. Bacterial pneumonia associated with aspiration develops over a few days and is more likely to arise if the amount of bacteria (inoculation dose) is large, the patient’s immune system is suppressed and there is underlying lung damage. The entry of oils and fatty substance into the lung causes inflammation followed by fibrotic scarring of the lung tissue.

Risk factors

Aspiration pneumonia is more likely to occur with one or more of the following risk factors and predisposing conditions.

  • Alcoholism.
  • Dementia.
  • Elderly patients with dysphagia, even without other diseases.
  • Epilepsy.
  • Coma.
  • Critical illnesses and debilitated patients.
  • Gastroesophageal reflux disease (GERD).
  • Iatrogenic – anesthesia (general), bronchoscopy, endoscopy (upper gastrointestinal), intubation (nasogastric or endotracheal). tracheostomy.
  • Neurological disorders like multiple sclerosis, myasthenia gravis and Parkinson’s disease.
  • Overdose – prescription drugs like sedatives or illicit drugs.
  • Stroke.
  • Traumatic head injury.
  • Vomiting that is severe and prolonged.

Bacteria

There are a number of different bacteria that can cause pneumonia and may reach the lung due to aspiration. The more common bacteria involved in aincludes :

  • Enterobacteriaceae species
  • Haemophilus influenzae
  • Pseudomonas aeruginosa
  • Staphylococcus aureus
  • Streptococcus pneumoniae

Diagnosis

The symptoms above, when seen in a patient with the risk factors, should warrant further diagnostic investigations to confirm a diagnosis of aspiration pneumonia. A chest x-ray may be sufficient to diagnose aspiration pneumonia but a sputum culture and various blood tests should also be conducted for further assessment. A sputum culture will definitively identify the causative bacteria while lood tests can confirm the presence of an infection, detect the spread of the bacteria, blood oxygen and and pH levels. Various other diagnostic investigations may also be conducted to diagnose the type of aspiration and assess the condition.

Treatment

The patient should firstly be stabilized by maintaining the integrity of the airway, breathing and circulation (ABC). Suctioning may be able to remove any aspirate in the mouth, throat or even the trachea. Oxygen supplementation along with IV fluids and electrolytes may also be necessary depending on the patient’s status. Intubation and mechanical ventilation may also be necessary.

Bacterial pneumonia should be treated with antibiotics. Clindamycin is the antibiotic of choice. Alternatively amoxicillin and metronidazole may be used. The antibiotics may initially be administered intravenously and then oral antibiotics continued once symptoms of aspiration pneumonia resolves. Patients with a lung abscess may need to continue the antibiotics for prolonged periods of time.

Chemical pneumonitis may not require any specific treatment measures beyond stabilizing the patient, suctioning the upper respiratory traction, intubation and ventilation. Antibiotics are often prescribed as a preventative measure but has not been shown to be necessary in every case of chemical pneumonitis. Corticosteroids that were often used for pneumonitis in the past but is not advisable as a routine measure.

References :

www.merckmanuals.com/professional/pulmonary_disorders/pneumonia/aspiration_pneumonitis_and_pneumonia.html

emedicine.medscape.com/article/296198-overview

www.patient.co.uk/doctor/Aspiration-Pneumonia.htm