Pneumonia

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Pneumonia

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A 58-year-old man goes to the emergency department for evaluation of fever and dry cough for the past week. He has also become progressively more dyspneic, and walking a single block makes him short of breath. He underwent a liver transplantation 4-months ago for treatment of autoimmune hepatitis and is currently taking several immunosuppressant drugs. Temperature is 38.5°C (101.3°F), pulse is 104/min, respirations are 20/min, blood pressure is 122/88 mmHg, and oxygen saturation is 89% on room air. Lung auscultation reveals bilateral crackles and rhonchi. Chest radiograph reveals bilateral, diffuse interstitial infiltrates extending from the perihilar region. Leukocyte count is 13,000/mm3 and serum lactate dehydrogenase level is 460 U/L. Further testing is most likely to reveal which of the following findings?  

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Pneumonia is an infection in the lung tissue caused by microbes, and the result is inflammation.

The inflammation brings water into the lung tissue, and that extra water can make it harder to breathe.

During inhalation, air reaches your lungs by traveling down your trachea, then it continues through the bronchi and the bronchioles and ends up in the alveoli.

The alveoli are tiny air sacs that look like tiny clumps of grapes, that are wrapped up in a net of capillaries. This is where the majority of gas exchange happens in the lungs.

Oxygen leaves the air in the alveoli and crosses into the bloodstream while carbon dioxide leaves the bloodstream and is then exhaled out of the body.

Now, now in addition to air, you’re constantly breathing in other stuff, like microbes. But we’re usually good at protecting ourselves.

For example, we have mechanical techniques like coughing, a mucociliary escalator that lines the entire airway and moves out larger bacteria, and macrophages that are nestled deep inside the alveoli and ready to destroy anything that lands there.

But sometimes, a particularly nasty microbe might succeed in colonizing the bronchioles or alveoli, and when that happens - Congratulations! You’ve got pneumonia.

Those microbes typically multiply and cross over from the airways into the lung tissue, creating an inflammatory response.

The tissue quickly fills with white blood cells as well as proteins, fluid, and even red blood cells if a nearby capillary gets damaged in the process.

Now, there are lots of different pneumonia-causing microbes.

Usually it’s caused by viruses and bacteria, but it can also be caused by fungi and a special class of bacteria called mycobacteria.

In adults, the most common viral cause of pneumonia is influenza, sometimes just called the flu.

Summary

Pneumonia is an infection of the lungs that results in air sacs being filled with fluid. It may be caused by bacteria, viruses, or fungal infections. Pneumonia is either community-acquired, meaning a person got sick outside of a hospital or healthcare setting; or hospital-acquired, which is when a person gets it when they are already hospitalized for something else. Common symptoms of pneumonia can include fever, cough, chest pain, shortness of breath, and difficulty breathing. The severity of symptoms can range from mild to severe. Treatment for pneumonia typically involves drugs to kill the invading pathogen and supportive care such as oxygen therapy.

Sources

  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 7/E (ENHANCED EBOOK)" McGraw Hill Professional (2014)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Pneumonia: update on diagnosis and management" BMJ (2006)
  6. "<i>Streptococcus pneumoniae</i>: Epidemiology, Risk Factors, and Clinical Features" Seminars in Respiratory and Critical Care Medicine (2005)
  7. "Community-acquired pneumonia" The Lancet (2015)
  8. "Intracellular Survival and Replication of &lt;i&gt;Legionella Pneumophila&lt;/i&gt; within Host Cells" YAKUGAKU ZASSHI (2008)
  9. "Epithelial Cells Infected with <i>Chlamydophila pneumoniae</i> ( <i>Chlamydia pneumoniae</i> ) Are Resistant to Apoptosis" Infection and Immunity (2001)
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