Pneumonia (Bacterial, Nonbacterial)

Photomicrograph of pneumonia– An acute infection and inflammation of the bronchioles, alveolar spaces, and interstitial tissue of the lung parenchyma.

Causes and Incidence

Pneumonia is caused by bacteria, viruses, fungi, or parasites. Predisposing factors include viral respiratory infections, alcoholism, smoking, age extremes, debility, dysphagia, altered consciousness, therapies that depress the immune system, and underlying disease states such as heart failure, chronic obstructive pulmonary disease, or immunosuppressive disorders. Individuals in hospitals for other disorders are also at high risk. Each year in the United States, more than 2 million people are found to have pneumonia and more than 50,000 of those individuals die, making pneumonia the sixth leading cause of death in the United States. In developing countries pneumonia is either the first or second leading cause of death. The most common types, which are bacterial, are Pneumococcus, Staphylococcus, Streptococcus, Klebsiella, and Haemophi-lus pneumonia.

Disease Process

Organisms reach the lung through aspiration, aerosolization, or hematogenous spread. This usually occurs through droplet inhalation or by aspiration of fluids in the oropharynx. Pneumonia results if a series of host defense mechanisms fails to keep the respiratory tree free of infection. Upper airway mechanisms such as nasal filtration may be bypassed, the normal flora altered, IgA secretion impaired, or the glottis depressed. Lower airway mechanisms such as coughing, cilia mucus, and mucociliary transport may be altered or impaired. Macrophages or cell-mediated immunity may be impaired, and immunoglobins, complement, or surfactant may be deficient in the alveoli.

The pathophysiology varies by etiologic agent. Bacterial pneumonia is marked by an intraalveolar suppurative exudate with consolidation. Mycoplasmal and viral pneumonias produce interstitial inflammation with infiltrate in the alveolar walls; there is no accompanying exudate or consolidation. Pneumococcal and streptococcal pneumonia have four distinct stages: (1) congestion, characterized by serous exudate, vascular engorgement, and rapid proliferation of the pathogen; (2) red hepatization, when RBCs, fibrin, and polymorphonuclear cells fill the alveoli; (3) gray hepatization, when leukocytes and fibrin pack the alveoli; and (4) resolution, marked by lysis and resorption of exudate by macrophages.

Viral pneumonia begins with an inflammatory response in the bronchi, which damages the ciliated epithelium. The lungs become congested and may be hemorrhagic. Intracellular viral inclusions form with many viruses. In aspiration pneumonia, the bacteria is aspirated with food or liquid. If the pH of the aspirated substance is below 2.5, atelectasis, pulmonary edema, and hemorrhage occur, followed by tissue necrosis and the formation of exudate.

Symptoms

Bacterial
Abrupt onset with shaking chills, cough, dyspnea, sputum production (often rust or salmon colored), pleurisy; nausea, vomiting, malaise, and myalgia also may be present

Viral
Headache, fever, myalgia, cough with mucopurulent sputum

Mycoplasmal
Malaise, sore throat, dry cough with rapid progression to productive cough with mucoid, purulent, and blood-streaked sputum

Fungal
(See Pneumocystis carinii Pneumonia)

Aspiration
Dyspnea, cyanosis, hypotension, tachycardia

Potential Complications

Septic shock, lung abscess, respiratory failure, bacteremia, endocarditis, pericarditis, and meningitis are possible complications.

Diagnostic Tests

Sputum examination
Must be obtained from lower respiratory tract–positive for pathogen

WBC count
Leukocytosis; neutrophilia in mycoplasmal or viral infection

Radiology
Consolidation in bacterial infection; bronchopneumatic type infiltrate in viral infection; clear in early mycoplasmal infection; atelectasis in aspiration pneumonia

Pulmonary function
Decreased lung volumes and compliance; increased airway resistance

Treatments

Surgery
Thoracentesis with chest tube if empyema or collapse occurs; tracheostomy if needed for patent airway.

Drugs
Antiinfective drugs (broad spectrum or specific to pathogen); analgesics for pain; prophylaxis with influenza vaccine and pneumococcal pneumonia vaccine in high-risk individuals.

General
Rest; humidification with nebulizer to loosen secretions; oxygen if PaO2 is below 60 mm Hg; coughing and deepbreathing exercises; adequate hydration to liquefy secretions; suctioning with copious secretions or compromised consciousness; mechanical ventilation for respiratory failure; adequate nutritional support with supplemental feedings or total parenteral nutrition if needed; monitoring of blood gases and general respiratory status.