Pathophysiology of Community Acquired Pneumonia

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Pneumonia is acute infection of the lung, that can be caused by an infectious agent such as bacteria, fungus, virus, or parasitic (Franco, 2017, p. 621). These infectious agents reach the lungs through several ways, either through aspiration, inhalation, or hematogenous spread from other infection in the body (Lewis et al., 2017, p. 500).

Pneumonia can be classified as community-acquired pneumonia (CAP), or hospital-acquired pneumonia (HAP). To be categorized as CAP, patient that has the pneumonia should not been hospitalized or resided in long-term care facility within the last 14 days from onset. For HAP, patient has the pneumonia within 48 hours after hospitalization, non-intubated and the symptoms was not present when patient was admitted (Lewis et al., 2017, p. 501).

Types of microorganism that causing CAP are almost bacterial, but about five to ten percent of the cases are caused by virus. The most common bacteria that causing CAP is Streptococcus pneumoniae, a gram-positive bacteria (Franco, 2017, p. 624). CAP also can be caused by fungal infection, and according to Central for Disease Control and Prevention (CDC), CAP that caused by fungus is on the rise in southwestern United States, like California or Arizona. The disease is named Coccidioidomycosis, or more well known as valley fever.

Despites of pneumonia types and different organism that causing it, the disease process is almost the same. After the infectious agent infiltrate the lungs, it triggers inflammatory reaction from the body. During the inflammation, the blood flow and the vascular permeability are increase. This increasement activates the neutrophils, type of white blood cells that engulf the microorganism. Since more and more neutrophils attracted to inflammation site, it causes edema in the airway and the fluid from the capillaries and the tissue goes to the alveoli. Alveoli that has fluid in it cannot do its job to exchange gas properly. This condition causes ventilation – perfusion mismatch (V/Q mismatch), leading to hypoxia, low oxygen level on tissue level (Lewis et al., 2017, p. 502). The condition which the alveoli is inflamed and filled with fluid is called congestion. The next progression of pneumonia is consolidation stage, where neutrophils, red blood cell and fibrin (exudates) fill the alveoli. Furthermore, in advance stage of consolidation, the fluid with red blood cell, fibrin and pulmonary cells in the alveoli forming a solid mass (Franco, 2017, p. 623).

Manifestation of pneumonia associated with bacterial infection or fungal infection are cough (either productive or nonproductive), fever, fatigue, pleuritic chest pain, shortness of breath, crackles on lung sounds, tachycardia, tachypnea, dyspnea (Lewis et al., 2017, p. 502). RS complaint of shortness of breath, cough and chest pain when she arrived in ASVH emergency room, which reflecting the pneumonia symptoms.

Common diagnostic studies that used to diagnosed pneumonia is chest radiography (chest x-ray). Since pneumonia causing inflammatory exudate, the x-ray will show opacification on the lobe(s) of the lung (Franco, 2017, p. 628). In RS’s chest x-ray result, there was several spots of opacification on left lower lobe shown, which conform the diagnosis, CAP on left lower lobe. From the x-ray result, physician also able to know that she did not have any complication from CAP, such as pleurisy (inflammation of pleura), pneumothorax, or pleural effusion (collection of fluid in pleural space).

Throat culture, blood culture and computed tomography (CT scan) also used to determine the cause agent of the pneumonia. Since RS was not responded to empiric antibiotic treatment (Azithromycin) on outpatient basis, CT scan result is very important to determine the right treatment. From the CT scan result, numerous nodules with ground glass opacification are noted on both lungs, which represent the congestion process of pneumonia. On the left lobe, CT scan noted nodular opacification that indicate consolidation stage. Atelectasis also seen on RS’s both lung bases. The CT finding could represent infection disease that can be caused either fungus or bacteria. Thus, RS’s physician and pulmonologist also diagnosed her with suspected valley fever while waiting for the culture resulted.

The main treatment for pneumonia is antibiotic therapy. For CAP, empiric antibiotic should be prescribed as soon as possible to prevent complication. For healthy people without comorbidities and has no allergy to azithromycin, macrolide (erythromycin, azithromycin, clarithromycin) is the first drug of choice. Tetracycline also can be used to treat CAP without comorbidities if patient has allergy to macrolide. RS reported that she had finished the azithromycin antibiotic prior hospitalization without any improvement in her condition. Based on CT result, RS than treated with treated with antifungal medication (Fluconazole) and antibiotic ?-lactam (Piperacillin-Tazobactam). 

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Pathophysiology of Community Acquired Pneumonia. (2022, Dec 07). Retrieved September 23, 2023 , from

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