• Thomas Niccol, Marcus Young, Natasha E Holmes, Kartik Kishore, Sobia Amjad, Michele Gaca, Rinaldo Bellomo, and Ary Serpa Neto.
• Department of Intensive Care, Austin Hospital, 145 Studley Rd, Heidelberg, Melbourne, VIC, Australia.
• Crit Care. 2025 Jan 31; 29 (1): 5454.

PurposeTo use natural language processing (NLP) to study the incidence, characteristics, trajectory, associations, and outcomes of hallucinations and disturbed behaviour in intensive care unit (ICU) patients.MethodsWe used NLP to scan clinical progress notes of a large cohort of ICU patients to detect words indicating that a patient had experienced hallucinations. We also used NLP to detected disturbed behaviour during ICU stay. Moreover, we studied the use of antipsychotic medications in a nested cohort. Finally, we obtained the demographics, trajectory, associations, and outcome of these patients.ResultsWe conducted a non-interventional, observational study of 7525 patients. We found that 625 (8.31%) had experienced hallucinations. Among these, 623 (99.7%) also had NLP-diagnosed behavioural disturbance (NLP-Dx-BD). In contrast, in patients without hallucinations, only 3274 (47.4%) were NLP-Dx-BD positive. Among the 2904 nested cohort patients with electronic medications data, 252 (8.7%) experienced hallucinations. Of these, 60 (23.8%) received medications compared with 147 (5.5%) (p < 0.001) patients without hallucinations. There was no difference on outcomes in patients with or without hallucination.ConclusionsHallucinations affect one in 12 ICU patients and are strongly associated with disturbed behaviour, and the use of antipsychotic medications. Hallucinations may represent another phenotype of critical illness associated neurocognitive dysfunction and require a dedicated research program.© 2025. The Author(s).

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