Pneumonia: Clinical

Pneumonia is due to inflammation of the lung alveoli from an infection. Typically, fluid that’s filled with white blood cells starts to fill up the alveoli, and that inflammatory fluid essentially replaces the air that’s normally in the alveoli, and that fluid interferes with gas exchange. 

Pneumonia typically causes a fever, cough, and shortness of breath, along with tachypnea and tachycardia, and occasionally hypoxemia. If the infection is near the pleural surface, it can cause pleuritic chest pain, which is pain that worsens with inspiration. On chest exam, there’s dullness on percussion; increased tactile fremitus, which is an increased sensation of vibration when palpating over the affected area and asking the individual to speak; and egophony, which is increased resonance of transmitted sounds and makes the letter “E” sound like the letter “A”. On auscultation, bronchial breath sounds or inspiratory crackles may be heard. 

The diagnosis of pneumonia is based on having clinical signs and symptoms along with abnormal chest imaging, most commonly a chest x-ray. In pneumonia, a chest x-ray typically shows either a lobar consolidation or a diffuse, interstitial infiltrate. Pneumonia has to be distinguished from atelectasis which is when there’s collapse of a region of the lung, a complication that often occurs in individuals after surgery. On a chest x-ray, atelectasis shows up as a wedge-shaped region with it’s apex at the hilum with an ipsilateral shift of structures due to volume loss. In contrast, in a pneumonia there’s usually normal or increased volume with a consolidation that doesn’t have an apex at the hilum and no shift in structures. Now, in addition to imaging, some lab tests suggestive of pneumonia include an elevated white blood cell count, and elevated markers of inflammation like procalcitonin and C-reactive protein. It’s thought that these generally increase much more in bacterial pneumonia versus viral pneumonia.  

For individuals with pneumonia, the next step is to figure out the setting in which the pneumonia developed. If the pneumonia was acquired anywhere in the community, but not in a hospital, it’s called community acquired pneumonia, or CAP. CAP can develop in anyone, but most commonly affects the elderly and individuals with underlying diseases like chronic obstructive pulmonary disease, or COPD, as well as alcoholism, or smoking. If the pneumonia was acquired more than 48 hours after admission to a hospital, it’s called hospital acquired pneumonia, or HAP. Finally, a subgroup of HAP called ventilator-associated pneumonia, or VAP, refers to pneumonia that was acquired more than 48 hours after endotracheal intubation. In the majority of cases, antibiotics are selected based on the most likely pathogens in a given situation, and this is called empiric coverage.