Hospital-acquired and ventilator-associated pneumonia: Clinical sciences

Pneumonia is a lung infection that results in inflammation of one or both lungs. Most often, it is caused by bacteria like Streptococcus pneumoniae; or 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, which is when a person develops pneumonia outside of a hospital or within 48 hours after hospital admission; and hospital-acquired pneumonia, or HAP, which develops after 48 hours from hospital admission. Finally, there’s a special subtype of HAP called ventilator-acquired pneumonia, or VAP, which refers to pneumonia that occurs in patients on mechanical ventilation, 48 hours after endotracheal intubation.

Now, when a patient presents with signs and symptoms suggestive of HAP or VAP, the first step is to obtain a focused history and physical examination and order labs such as CBC and procalcitonin. You should also use pulse oximetry to check oxygen saturation levels, and collect a blood sample for cultures. Finally, don’t forget to obtain imaging, such as chest x-ray or point-of-care lung ultrasound.

Alright, first, let’s talk about the diagnosis and acute management of patients with HAP. Let's start with History. These patients usually report a fever, productive cough, pleuritic chest pain, and shortness of breath. Keep in mind that these symptoms develop at least 48 hours after admission. Now, the physical examination typically reveals elevated temperature, tachypnea, and tachycardia, as well as rales, and decreased breath sounds. When it comes to labs, they are likely to show elevated WBC count and procalcitonin levels, while pulse oximetry can reveal a drop in oxygen saturation. Finally, a chest X-ray usually reveals a new lung infiltrate, consolidation, or effusion.

Now, if a patient presents with these findings, you can diagnose HAP and start acute management. This means that you need to provide continuous monitoring of the heart rate, blood pressure, and oxygen saturation. Also, if needed, be sure to provide supplemental oxygen to keep the oxygen saturation above 92%. The next step is to find the causative organism through microbiological testing. This involves collecting sputum samples, usually by sputum induction. To do this, the patient should first inhale a saline mist, which will trigger a reflexive cough to release sputum from the lower airways. Sputum samples are then sent to the laboratory for gram staining and cultures. Additionally, if you suspect MRSA infection, sputum and nasopharyngeal swab samples can be sent for multiplex PCR studies.

Alright, let’s switch gears and talk about the diagnosis and acute management of patients with VAP. Patients with suspected VAP are typically sedated and intubated, so you won’t be able to get the history from them. So, discuss with other hospital staff and look through the medical chart for information like the time of intubation or a history of purulent secretions. The physical examination usually reveals signs like fever, tachycardia, rales, and decreased breath sounds. Keep in mind that these signs develop 48 hours after intubation.

Similarly to HAP, labs usually show elevated WBCs and procalcitonin, while oxygen saturation might be low. However, unlike HAP, the imaging of choice for VAP is a point-of-care lung ultrasound because it’s ideal for patients who can’t be easily transported. Common findings include subpleural consolidation, liver-like echogenicity of the lung, and dynamic air bronchograms.

Okay, if a patient presents with these findings, you can diagnose VAP, and you should start acute management immediately. Just like before, you will need to provide continuous monitoring of their heart rate, blood pressure, and oxygen saturation. Additionally, be sure to regularly assess ventilatory parameters and adjust the ventilator settings to maximize oxygenation.

Once the acute management is started, your next step is to look for the causative organism through microbiological testing. Remember that patients with VAP are intubated, therefore the induced sputum technique is not possible. Alternative techniques to collect sputum include bronchoalveolar lavage, or BAL for short, and mini-BAL. In BAL, a bronchoscope is inserted through the trachea into the lungs to reach a terminal segment of the affected lung lobe, inject sterile saline, and then suction a sample. On the other hand, in mini-BAL, a telescoping catheter is inserted through the endotracheal tube into the lower airways to obtain a sample. Regardless of the collection technique, you will send the sputum samples to the laboratory for gram staining, cultures, and possibly multiplex PCR studies if MRSA is suspected.