Ventilator-associated pneumonia (VAP) is a type of lung infection that occurs in people who are on mechanical ventilation breathing machines in hospitals. As such, VAP typically affects critically ill persons that are in an intensive care unit (ICU) and have been on a mechanical ventilator for at least 48 hours. VAP is a major source of increased illness and death. Persons with VAP have increased lengths of ICU hospitalization and have up to a 20–30% death rate. The diagnosis of VAP varies among hospitals and providers but usually requires a new infiltrate on chest x-ray plus two or more other factors. These factors include temperatures of >38 °C or <36 °C, a white blood cell count of >12 × 109/ml, purulent secretions from the airways in the lung, and/or reduction in gas exchange.
A different less studied infection found in mechanically ventilated people is ventilator-associated tracheobronchitis (VAT). As with VAP, tracheobronchial infection can colonise the trachea and travel to the bronchi. VAT may be a risk factor for VAP.
Signs and symptoms
People who are on mechanical ventilation are often sedated and are rarely able to communicate. As such, many of the typical symptoms of pneumonia will either be absent or unable to be obtained. The most important signs are fever or low body temperature, new purulent sputum, and hypoxemia (decreasing amounts of oxygen in the blood). However, these symptoms may be similar for tracheobronchitis.
Cause
Risk factors
Risk factors for VAP include underlying heart or lung disease, neurologic disease, and trauma, as well as modifiable risk factors such as whether the head of the bed is flat (increased risk) or raised, whether the patient had an aspiration event before intubation, and prior antibiotic exposure. As a result of intubation many of the body's defenses against infections are reduced or impaired; this can result in an ability for microorganisms to enter and cause infection. Patients who are in the ICU for head trauma or other severe neurologic illness, as well as patients who are in the ICU for blunt or penetrating trauma, are at especially high risk of developing VAP. Further, patients hospitalized for blunt trauma are at a higher risk of developing VAP compared to patients with penetrating trauma.
Ventilator-associated tracheobronchitis may be a risk factor for VAP, though not all cases of VAT progress to VAP.
Recent studies have also linked the overall oral health of a patient to the potential development of VAP; suggesting that bacteria found in plaque can "migrate to the respiratory system."
Microbiology
The microbiologic flora responsible for VAP is different from that of the more common community-acquired pneumonia (CAP). In particular, viruses and fungi are uncommon causes in people who do not have underlying immune deficiencies. Though any microorganism that causes CAP can cause VAP, there are several bacteria which are particularly important causes of VAP because of their resistance to commonly used antibiotics. These bacteria are referred to as multidrug resistant (MDR).