A 57-year old man has been in the hospital in New York City on a ventilator for

Question

A 57-year old man has been in the hospital in New York City on a ventilator for 3 days when he developed a severe pneumonia characterized by grossly bloody sputum. The doctors immediately started him on cephalosporin, a broad spectrum antibiotic, and send a sputum sample to the lab for identification. The test comes back showing a Gram negative coccobacilli resistant to all of the -lactams, including cephalosporins, fluoroquinolones, aminoglycosides, and the carbapenems. The doctors begin to treat the pneumonia aggressively with a new antibiotic, tigecycline. Fortunately, the patient responds to treatment and begins to improve. What is the most likely cause of the man’s nosocomially acquired pneumonia? What is one other cause of pneumonia?

Explanation / Answer

What is the most likely cause of the man’s nosocomially acquired pneumonia?
Ventilator-associated pneumonia (VAP) is defined as pneumonia that occurs 48-72 hours or thereafter following endotracheal intubation, characterized by the presences of a new or progressive infiltrate, signs of systemic infection (fever, altered white blood cell count), changes in sputum characteristics, and detection of a causative agent. VAP is estimated to occur in 9-27 % of all mechanically ventilated patients, with the highest risk being early in the course of hospitalization. It is the second most common nosocomial infection in the intensive care unit (ICU) and the most common in mechanically ventilated patients.
The complex interplay between the endotracheal tube, presence of risk factors, virulence of the invading bacteria and host immunity largely determine the development of VAP. The presence of an endotracheal tube is by far the most important risk factor, resulting in a violation of natural defense mechanisms (the cough reflex of glottis and larynx) against micro aspiration around the cuff of the tube. Infectious bacteria obtain direct access to the lower respiratory tract via:
(1) micro aspiration, which can occur during intubation itself;
(2) development of a biofilm laden with bacteria (typically Gram-negative bacteria and fungal species) within the endotracheal tube;
(3) pooling and trickling of secretions around the cuff; and
(4) impairment of mucociliary clearance of secretions with gravity dependence of mucus flow within the airways.
Pathogenic material can also collect in surrounding anatomic structures, such as the stomach, sinuses, nasopharynx and oropharynx, with replacement of normal flora by more virulent strains. This bacterium-enriched material is also constantly thrust forward by the positive pressure exerted by the ventilator. Whereas reintubation following extubation increases VAP rates, the use of non-invasive positive pressure ventilation has been associated with significantly lower VAP rates. Host factors such as the severity of underlying disease, previous surgery and antibiotic exposure have all been implicated as risk factors for development of VAP.
In addition, it has recently been noted that critically ill patients may have impaired phagocytosis and behave as functionally immunosuppressed even prior to emergence of nosocomial infection. This effect is attributed to the detrimental actions of the anaphylatoxin, C5a, which impairs neutrophil phagocytic activity and impairs phagocytosis by neutrophils. More recently, a combined dysfunction of T-cells, monocytes, and neutrophil’s has been noted to predict acquisition of nosocomial infection . For example, elevation of regulatory T-cells , monocyte deactivation (measured by monocyte HLA-DR expression) and neutrophil dysfunction (measured by CD88 expression), have cumulatively shown promise in predicting infection in the critically ill population, as compared to healthy controls
What is one other cause of pneumonia?
Aspiration pneumonia is a complication of pulmonary aspiration. Pulmonary aspiration is when you inhale food, stomach acid, or saliva into your lungs. You can also aspirate food that travels back up from your stomach to your esophagus.
All of these things may carry bacteria that affect your lungs. Healthy lungs can clear up on their own. If they don’t, pneumonia can develop as a complication.
Pneumonia from aspiration can occur when your defenses are impaired and the aspirated contents have a large amount of harmful bacteria.
You can aspirate and develop pneumonia if your food or drink “goes down the wrong way.” This may happen even if you can swallow normally and have a regular gag reflex. In that case, most of the time you’ll be able to prevent this by coughing. Those who have impaired coughing ability, however, may not be able to.

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