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

Purpose: 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.

Methods: 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.

Results: 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.

Conclusion: [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.