Community-acquired pneumonia: Clinical sciences

Pneumonia is a lung infection that results in inflammation of one or both lungs. Usually, it is caused by bacteria, like Streptococcus pneumoniae; and viruses, such as influenza, but rarely, pneumonia can be caused by fungi as well.

Now, based on the setting in which pneumonia develops, we can subdivide it into two main types: community-acquired pneumonia, or CAP for short; and hospital-acquired pneumonia, or HAP. When a person develops pneumonia outside of a hospital or within 48 hours after the admission to hospital, it’s considered CAP.

On the other hand, HAP develops after 48 hours of the admission to hospital. Finally, there’s a special subtype of HAP called ventilator-acquired pneumonia, or VAP. VAP refers to pneumonia that occurs in individuals on mechanical ventilation, 48 hours after the endotracheal intubation.

The first thing to do when approaching a patient with suspected CAP is to obtain a focused history and physical examination; send labs, such as ABG, CBC and BMP; monitor pulse oximetry; and get a chest x-ray.

Let’s start with the history. Patients with CAP might report coughing, difficulty breathing, and chest pain during inspiration. Keep in mind that these symptoms develop either outside of the hospital or within 48 hours of admission. They may also have a history of risk factors like COPD, diabetes, smoking, or alcohol use.

Here are some high-yield facts to keep in mind! A productive cough can occur with bacterial infections. However, if the sputum is blood-tinged, consider specific organisms like Streptococcus pneumoniae, Klebsiella pneumoniae, or Legionella pneumophila.

Now, the physical examination often reveals an elevated temperature, tachypnea, and tachycardia. Pay close attention to lung auscultation, which might reveal rales over the affected area. Additionally, if there’s lobar consolidation, the physical exam might demonstrate bronchial breath sounds, egophony, and increased tactile fremitus in the affected lobe.

In contrast, patients with a pleural effusion might present with decreased breath sounds, decreased tactile fremitus, and dullness to chest percussion in the affected area.

Finally, pulse oximetry might reveal a drop in oxygen saturation, while chest X-ray can show new lung infiltrates.

Once you diagnosed CAP based on the history and physical, labs, and imaging studies, the next step is to determine its severity. This is where the pneumonia severity index, or PSI, comes in. PSI categorizes patients into 5 classes based on clinical elements like age and temperature; laboratory elements, such as BUN and glucose; and radiographic elements, like pleural effusion.

Now, let’s talk about low-risk CAP. Classes 1 to 3 are considered low-risk CAP and can be managed at home. The type of treatment is based on whether or not the person has any chronic medical conditions. So, if your patient has no chronic conditions, start them on oral amoxicillin or doxycycline for 5 days. However, if they do have a chronic condition, such as COPD or diabetes mellitus, then make sure to start them on an oral respiratory fluoroquinolone like levofloxacin or moxifloxacin, or a combination of an oral beta-lactam and a macrolide for 5 days.

Okay, let’s switch gears and talk about high-risk CAP. Classes 4 and 5 are considered high-risk CAP and require admission to the hospital. First, use the Infectious Diseases Society of America/ American Thoracic Society CAP criteria, better known as IDSA/ATS CAP criteria, to determine if they should be managed on the hospital floor, or in the ICU. IDSA/ATS CAP criteria include major criteria, such as septic shock or respiratory failure; and minor criteria, like elevated respiratory rate, confusion, uremia, high WBC count, low platelets, hypothermia, multilobar infiltrates, and hypotension.

Now, if your patient has no major or less than 3 minor criteria, admit them to the hospital floor and start them on supplemental oxygen to maintain oxygen saturation above 92%. Additionally, you should look for a causative pathogen, so don’t forget to obtain a blood culture, and a sputum sample for culture and gram stain. You can also test the urine and sputum for pneumococcal antigens. Finally, assess their symptoms daily to check how they are responding to treatment.

If your patient has 1 major or 3 or more minor criteria, admit them to the ICU and start the same treatment as you do for hospital floor patients. Additionally, if the patient presents with respiratory failure, put them on ventilatory support and periodically assess parameters to optimize oxygenation. However, if the patient presents with sepsis, you should also maintain their systolic blood pressure above 90 mmHg using IV fluids and vasopressors.