Selective impairment of auditory discrimination in critically ill patients with delirium: a prospective electroencephalographic observational study.

Background: Delirium in the ICU is a major and potentially modifiable risk factor for subsequent neurocognitive decline. However, the cerebral dysfunctions underlying its behavioural manifestations remain poorly understood, limiting targeted clinical management. These dysfunctions may reflect impairments in low-level perceptual processes (stimulus detection), higher-order integrative processes (stimulus discrimination), or both. The P3 event-related potential (ERP), a positive deflection in the electroencephalogram occurring approximately 300 ms after stimulus presentation, reflects neural processes involved in attention and cognitive integration and provides an objective measure of auditory detection (P3a) and discrimination (P3b). Methods: In this prospective single-centre observational study conducted between March and October 2021 in the Critical Care Unit of Purpan University Hospital, Toulouse, France, we used a multidimensional P3 ERP battery incorporating auditory paradigms designed to assess stimulus detection (P3a) and discrimination (P3b). The battery included both non-verbal stimuli (local-global paradigm) and verbal stimuli (subject's own name and arithmetic paradigms). Critically ill COVID-19 patients with delirium (n=18) and without delirium (n=20) were prospectively recruited. The primary outcome was the presence of P3 subcomponents across paradigms. Group differences were assessed using spatial-temporal cluster-based permutation testing, with statistical significance defined at cluster-level P≤0.05. Results: In patients without delirium, both detection-related (P3a) and discrimination-related (P3b) responses were present across verbal and non-verbal paradigms. In contrast, patients with delirium demonstrated preserved P3a responses to non-verbal auditory stimuli but absence of P3b responses, indicating impaired auditory discrimination (cluster-level P≤0.05). Source modelling suggested reduced activation of frontal cortical generators in patients with delirium compared with those without delirium. Conclusions: In critically ill patients with COVID-19, delirium was associated with preserved automatic auditory detection but impaired higher-order auditory discrimination. This dissociation provides neurophysiological evidence of selective impairment in integrative cognitive processing during ICU delirium and contributes to improved mechanistic understanding of delirium-related brain dysfunction.