Pathophysiology of Community Acquired Pneumonia

Pneumonia is a severe infection of the lung that can be caused by a contagious agent such as bacteria, fungus, virus or parasites (Franco, 2017, p. 621). These transmittable agents reach the lungs through various methods, such as inhalation, breathing or hematogenous spread from other infections in the body (Lewis et al., 2017, p. 500).

Pneumonia can be categorized as community-acquired pneumonia (CAP) or hospital-acquired pneumonia (HAP). To be classified as CAP, the individual with pneumonia should not have been hospitalized or lived in a long-term care center within the last two weeks.

As for HAP, the individual contracts pneumonia within two days after hospitalization, non-intubation, and the symptoms were not present upon admission (Lewis et al., 2017, p. 501).

The types of microbes causing CAP are mainly bacterial, but around five to ten percent of the cases are caused by viruses. The most common bacterium causing CAP is Streptococcus pneumoniae, a gram-positive bacterium (Franco, 2017, p. 624). CAP can also be caused by a fungal infection, and according to the Centers for Disease Control and Prevention (CDC), CAP caused by fungi is increasing in the southwestern USA, like California or Arizona. The disease is named Coccidioidomycosis, also known as valley fever.

Despite the type of pneumonia and the different organisms causing it, the disease process is almost the same. When the infectious agent penetrates the lungs, it provokes an inflammatory response from the body. During the inflammation, blood flow and vascular permeability increase. This increase stimulates the neutrophils, a type of white blood cell that engulfs the organisms. As more and more neutrophils are attracted to the inflammation site, it induces edema in the respiratory tract, and the fluid from the capillaries and tissues shifts to the alveoli. Alveoli filled with fluid cannot perform their gas exchange function properly. This condition causes a ventilation-perfusion mismatch (V/Q mismatch), leading to hypoxia, a condition of low oxygen level at the cellular level (Lewis et al., 2017, p. 502). The stage in which the lungs are inflamed and filled with fluid is called congestion. The next stage of pneumonia is consolidation, where neutrophils, red blood cells, and fibrin (exudates) fill the alveoli. Additionally, in the subsequent phase of consolidation, the fluid with red blood cells, fibrin, and lung cells in the lungs creates a solid mass (Franco, 2017, p. 623).

Symptoms of pneumonia linked to bacterial or fungal infection include cough (either productive or nonproductive), fever, exhaustion, pleuritic chest pain, shortness of breath, crackles on lung sounds, tachycardia, tachypnea and dyspnea (Lewis et al., 2017, p. 502). RS's complaints of shortness of breath, cough, and chest pain when she arrived at ASVH emergency room are suggestive of pneumonia symptoms.

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