Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders

Pneumonia

Pneumonia is an acute infection of the lung parenchyma that commonly impairs gas exchange. The prognosis is generally good for people who have normal lungs and adequate host defenses before the onset of pneumonia.

Pneumonia is commonly classified according to location: bronchopneumonia involves distal airways and alveoli; lobular pneumonia, part of a lobe; lobar pneumonia, an entire lobe. It can also be classified according to the causative agent, such as gram negative or gram positive, viral, bacterial, or the specific organ responsible such as pneumococcal pneumonia. Nosocomial pneumonia occurs during hospitalization for another condition.

Age Alert

Older patients and very young patients are at greater risk for pneumonia.

Causes

Primary

·         Inhalation or aspiration of a pathogen, including pneumococcal, viral, and mycoplasmal pneumonia

Secondary

·         After initial damage from a noxious chemical or other insult (superinfection)

·         Hematogenous spread of bacteria from a distant focus

Pathophysiology

In bacterial pneumonia, an infection initially triggers alveolar inflammation and edema. This produces an area of low ventilation with normal perfusion. Capillaries become engorged with blood, causing stasis. As the alveolocapillary membrane breaks down, alveoli fill with blood and exudate, resulting in atelectasis.

In viral pneumonia, the virus first attacks bronchiolar epithelial cells. This causes interstitial inflammation and desquamation. The virus also invades bronchial mucous glands and goblet cells. It then spreads to the alveoli, which fill with blood and fluid. In advanced infection, a hyaline membrane may form.

In aspiration pneumonia, inhalation of gastric juices or hydrocarbons triggers inflammatory changes and inactivates surfactant over a large area. Decreased surfactant leads to alveolar collapse. Acidic gastric juices may damage the airways and alveoli. Particles containing aspirated gastric juices may obstruct the airways and reduce airflow, leading to secondary bacterial pneumonia.

Signs and symptoms

·         Coughing

·         Sputum production

·         Pleuritic chest pain

·         Shaking chills

·         Fever

·         Wide range of physical signs, from diffuse, fine crackles to signs of localized or extensive consolidation and pleural effusion

·         Dyspnea

·         Tachypnea

·         Malaise

·         Decreased breath sounds

Diagnostic test results

·         Chest X-rays identify infiltrates that confirm the diagnosis.

·         Sputum specimen, Gram stain, and culture and sensitivity tests differentiate the type of infection.

·         White blood cell (WBC) count indicates leukocytosis in bacterial pneumonia, and a normal or low WBC count in viral or mycoplasmal pneumonia.

·         Blood cultures reflect bacteremia and are used to determine the causative organism.

·         Arterial blood gas levels vary, depending on the severity of pneumonia and the underlying lung state.

·         Bronchoscopy or transtracheal aspiration allows the collection of material for culture.

·         Pulse oximetry shows a reduced oxygen saturation level.

Treatment

·         Antimicrobial therapy (varies with causative agent)

·         Humidified oxygen therapy

·         Mechanical ventilation

·         High-calorie diet and adequate fluid intake

·         Bed rest

·         Analgesics

·         Positive end-expiratory pressure to facilitate adequate oxygenation in patients on mechanical ventilation for severe pneumonia

P.101

TYPES OF PNEUMONIA

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