Pneumonia II: Pathophysiology

Pathogens enter the respiratory tract through regular inhalation, aspiration of oropharyngeal flora, or as bloodborne organisms trapped in the pulmonary capillary bed. Once they reach the alveoli, pathogens invade cells and multiply, triggering an immune response that leads to inflammation and exudate formation. This process disrupts normal gas exchange and reduces oxygen reaching the bloodstream.

During pneumonia, white blood cells migrate to infected alveoli and multiply, causing consolidation. An exudate of cellular debris, microorganisms, and fluid fills the alveoli and bronchioles. This accumulation increases capillary permeability, allowing more fluid to leak into the alveolar spaces and leading to hypoventilation and impaired gas exchange.

The consolidation and inflammation in the alveoli hinder the exchange of oxygen and carbon dioxide. Fluid and pus accumulation disrupts normal gas exchange, reducing the quantity of oxygen that reaches the bloodstream. This impaired gas exchange leads to dyspnea, tachypnea, and hypoxia as the body compensates for insufficient oxygen delivery.

Common respiratory symptoms include a cough that may be productive with green, yellow, or rust-colored sputum, dyspnea, tachypnea, and pleuritic chest pain characterized by sharp sensations worsened by deep breaths or coughing. Crackles may be heard on auscultation, and breath sounds may be diminished over areas of consolidation.

Systemic symptoms include fever and shaking chills indicating an immune response to infection, along with fatigue, headache, diaphoresis, anorexia, and myalgia. Severe pneumonia may present with flushed cheeks and central cyanosis. Confusion or altered mental status can occur, particularly in older adults, sometimes as the sole indication of pneumonia.

The immune system can clear the infection with proper treatment, and alveolar exudate can be reabsorbed or coughed up. However, complications may occur such as abscess formation, spread of infection to the pleural cavity causing pleurisy or empyema, or bacteremia if bacteria enter the bloodstream, potentially leading to pneumonia iii complications and assessment.

The respiratory tract has defense mechanisms like mucociliary clearance and cough reflex that normally prevent pathogenic organisms from establishing infection. If these defenses are compromised or the pathogen is highly virulent, infection can occur. Understanding these mechanisms helps explain why certain patients are at higher risk for developing pneumonia.