The multistep road to ventilator-associated lung abscess: A retrospective study of S.aureus ventilator-associated pneumonia

Abstract

Object: We observed some cases of lung abscess (LA) in ICU patients suffering S.aureus ventilator-associated pneumonia (S.aureus-VAP). We aimed to assess which of the host and/or bacteria-related features are associated with LA.

Methods: We conducted a retrospective study from January 2009 to July 2013 in a trauma surgical ICU within a teaching hospital. All adult patients presenting with S.aureus-VAP were included. We compared two groups of patients according to the formation or not of LA concomitantly to S.aureus-VAP.

Results: Seventy-nine S.aureus-VAP patients, predominantly males (85%) of rather young age (mean [SD]: 35yr [21-64]) with severe trauma (initial Simplified Acute Score II = 42 [32-52]) related-ICU admission, were included. Among them, 10 (14%) developed LA. Patient's characteristics significantly associated with LA development were: a younger age (p = 0.003), road traffic accidents admission (p = 0.017), head injury (p = 0.002), lower Glasgow Coma Scale (p = 0.009), blunt chest trauma (p = 0.01) pneumothorax (p = 0.01) and lung contusions (p = 0.002). No microbiological factors were significantly associated with LA formation. Abscesses were mostly bilateral, ≥5 cm of diameter and with a posterior location.

Conclusions: Our results do not favor a specific virulence of S.aureus, but rather highlight the role of multiple insults to the lung, promoting LA formation. Despite a similar severity score, patients with LA had more serious trauma, combining severe both chest and head insults.

Fig 1. Flow chart of the study.

Exclusion criteria: (i): pneumonias that were not associated with mechanical ventilation; (ii) patients with preexisting (ICU admission) major lung insult (e.g.; important emphysema or antecedent of lung abscess), (iii) patients suffering from α1-antitrypsin deficiency or cystic fibrosis, (v) VAP without microbiological documentation, (vi) all situations when futility of care within the first 48h following diagnosis was anticipated, (vii) and death within the first 48h. Cfu, colony forming unit; VAP, ventilator associated pneumonia.

Fig 2. CT scan on admission (A) and under mechanical ventilation (B) of 4 patients presenting an abscess (1, 2, 3, and 4).

We selected the most obvious lung abscesses. In the first place, CT scan illustrated that abscess occurred in the most contused area. Secondly, these images allowed us to appreciate the size and shape of the abscess. The thin-walled cavity and its surrounding consolidation appear.