In this episode, I’ll discuss bacterial density as a therapeutic indicator for ventilator-associated tracheobronchitis due to pseudomonas.
Bacterial density refers to how many colony-forming units of bacteria are found in a given culture and is reported as log10 CFU/mL.
The bacterial density of Pseudomonas relates to its pathogenicity.
Authors in the journal Critical Care recently published a retrospective analysis of mechanically ventilated ICU patients with Pseudomonas isolated from endotracheal aspirates to determine the relationship between peak Pseudomonas density and weaning from mechanical ventilation.
Patients were divided into three groups (low, moderate, and high) according to the peak Pseudomonas density during ICU stay. The breakdown of each group was as follows: low (≤ 10^4 cfu/mL), moderate (10^5‒10^6 cfu/mL), and high (≥ 10^7 cfu/mL) peak density groups.
Over 400 patients were analyzed. The high density group had worse outcomes compared to the low density group, with an odds ratio of 2.78 for ICU mortality. Ventilator free days were significantly higher in the low density group compared to the high density group as well.
3 risk factors for a high density of Pseudomonas were identified:
1. More than 28 days of mechanical ventilation
2. Hyperglycemia
3. Use of non-antipseudomonal cephalosporins during the ICU stay
Only in the high density group did appropriate antibiotic therapy result in more ventilator free days than if inappropriate antibiotic therapy was given, compared to no difference in the low and moderate groups based on appropriateness of antibiotic therapy. This suggests that bacterial density could identify which patients might benefit from antibiotic therapy. This has implications for antibiotic stewardship although it should be confirmed by a prospective study.
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