Aspiration pneumonia

Aspiration pneumonia
Name	Aspiration pneumonia
Synonyms	Anaerobic pneumonia
Field	Pulmonology, Infectious disease (medical specialty)
Symptoms	Fever, cough, dyspnea
Complications	Lung abscess, Empyema, Acute respiratory distress syndrome
Risks	Dysphagia, Gastroesophageal reflux disease, Altered mental status
Diagnosis	Chest radiograph, Sputum culture, Computed tomography
Treatment	Antibiotic therapy, Oxygen therapy, Respiratory therapy
Medication	Clindamycin, Piperacillin/tazobactam
Prognosis	Variable, higher mortality in elderly

Aspiration pneumonia is a type of lung infection resulting from the inhalation of oropharyngeal or gastric contents into the lower respiratory tract. It is distinct from chemical pneumonitis, which is an inflammatory reaction to sterile aspirated material. This condition is a common and serious complication in patients with impaired swallowing mechanisms or consciousness, often leading to significant morbidity and mortality, particularly among hospitalized and elderly populations.

Definition and overview

Aspiration pneumonia is formally defined as an infectious process caused by the inhalation of pathogenic bacteria from the oropharynx or stomach. It is a major subset of pneumonia and is frequently encountered in clinical settings such as hospitals, nursing homes, and intensive care units. The Centers for Disease Control and Prevention and the Infectious Diseases Society of America provide guidelines for its diagnosis and management. Key differentiators from other pneumonias include the specific circumstances of aspiration and the often polymicrobial, anaerobic nature of the infection, involving organisms like Peptostreptococcus and Bacteroides.

Causes and risk factors

The primary cause is the entry of contaminated secretions or substances past the laryngeal protective reflexes. Major risk factors are conditions that compromise the gag reflex or level of consciousness, including stroke, seizure disorders, general anesthesia, and excessive alcohol or drug use. Neurological diseases such as Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis are strongly associated. Structural abnormalities like Zenker's diverticulum or a history of esophageal cancer surgery also increase risk. Medications, particularly sedatives and antipsychotics, and conditions like diabetes mellitus and dental caries further predispose individuals.

Pathophysiology

The pathophysiology begins when aspirated material, laden with bacteria from the gingival crevice or gastric acid, bypasses the defenses of the upper airway. This leads to inoculation of the lung parenchyma, most commonly in the dependent bronchopulmonary segments such as the right lower lobe. An initial chemical injury from gastric acid can damage the alveolar-capillary membrane, facilitating bacterial invasion. The ensuing inflammatory response involves neutrophils and cytokines, leading to consolidation and the clinical syndrome of pneumonia. Anaerobic bacteria thrive in the necrotic tissue, potentially leading to complications like necrotizing pneumonia.

Clinical presentation and diagnosis

Patients often present with symptoms such as fever, productive cough with foul-smelling sputum, pleuritic chest pain, and tachypnea. Physical exam may reveal crackles or egophony on auscultation. Diagnosis relies on a combination of clinical history suggesting aspiration, imaging, and microbiologic studies. A chest X-ray typically shows infiltrates in characteristic locations. Advanced imaging with CT scan of the chest may reveal cavitation or pleural effusion. Sputum Gram stain and culture, and sometimes bronchoscopy with bronchoalveolar lavage, are used to identify causative organisms, though treatment is often empiric based on guidelines from the American Thoracic Society.

Treatment and management

Initial management involves securing the airway and providing supplemental oxygen. The cornerstone of treatment is prompt administration of empiric antibiotics effective against oral anaerobes and Gram-negative bacilli. Common regimens include clindamycin, ampicillin-sulbactam, or a carbapenem. Supportive care includes chest physiotherapy and postural drainage. In severe cases, management in an intensive care unit with mechanical ventilation may be necessary. Treatment duration is typically longer than for community-acquired pneumonia, and therapy may be adjusted based on culture results from institutions like the Mayo Clinic or Cleveland Clinic.

Prevention and prognosis

Prevention strategies focus on mitigating risk factors, including careful management of sedation during procedures, elevation of the head of the bed, and assessment by a speech-language pathologist for dysphagia. For high-risk patients, interventions like proton-pump inhibitors or enteral feeding via percutaneous endoscopic gastrostomy may be considered. Prognosis varies widely; mortality is significant, especially among the elderly, those in long-term care facilities, or patients with severe comorbidities like congestive heart failure. Outcomes are generally worse than for typical bacterial pneumonia, with higher rates of recurrence and complications such as empyema requiring thoracentesis.

Category:Pulmonology Category:Infectious diseases