[¹⁸F]FDG PET/CT identifies infectious and inflammatory foci in persistent critical illness

Some ICU patients remain critically ill despite reversal of the original admission diagnosis, driven by a cascade of events resulting in new and persistent organ failure. Secondary infections and systemic inflammation are important components of this cascade and may be visualised using [¹⁸F]FDG PET/CT. The aim of this dual centre retrospective study was to assess the ability of [¹⁸F]FDG PET/CT to identify infectious and inflammatory foci in patients with persistent critical illness and to evaluate its impact on subsequent therapy management.

We included patients admitted to the ICU between 2017 and 2024, in whom a [¹⁸F]FDG PET/CT scan was performed ten days or more after ICU admission. [¹⁸F]FDG PET/CT reports were reviewed for diagnoses, and clinical records were reviewed to determine if this diagnosis was new, which diagnostics were performed before the PET/CT, and which therapeutic changes were made directly after the PET/CT. The relation between inflammatory parameters and [¹⁸F]FDG PET/CT findings were studied using t-test or ANOVA.

Forty-seven patients with persistent critical illness were included from two university medical centres. The median interval between admission and PET/CT was 21 days (IQR 14-28). In 43 patients (91%) a potential infectious or inflammatory focus was detected, of which 34 (72%) were previously unknown. The [¹⁸F]FDG PET/CT was utilized late in the diagnostic work-up since a median of 7 (IQR 6.0-8.0) diagnostic procedures were performed prior to the PET/CT. In 26 (55%) patients therapy change was reported within 48 h after the PET/CT.

[¹⁸F]FDG PET/CT detected a considerable number of (new) infectious and inflammatory foci in patients with persistent critical illness, often followed by a change in therapy. Further research is needed to establish the role of [¹⁸F]FDG PET/CT in these patients.