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Purpose: To 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., Methods: We 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., Results: We 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., Conclusions: Hallucinations 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., Competing Interests: Declarations. Ethical approval and consent to participate: This study was approved by the Austin Hospital Human Research Ethics Committee (LNR/19/Austin/38), which waived the requirement for informed consent. Consent for publication: The authors hereby provide consent for this manuscript titled "Hallucinations and Disturbed Behaviour in the Critically Ill: Incidence, Patient Characteristics, Associations, Trajectory, and Outcomes" to be published. The authors confirm that they have read and approved the final version of the manuscript. They further affirm that the work described in the manuscript is original and has not been published elsewhere. Competing interest: The authors declare no competing interests., (© 2025. The Author(s).)

Competing Interests: All authors declare that they do not have any potential conflict of interest in relation to this manuscript.

Objectives: Mechanically ventilated patients account for about one-third of all admissions to the intensive care unit (ICU). Ketamine has been conditionally recommended to aid with analgesia in such patients, with low quality of evidence available to support this recommendation. We aimed to perform a narrative scoping review of the current knowledge of the use of ketamine, with a specific focus on mechanically ventilated ICU patients. Methods: We searched MEDLINE and EMBASE for relevant articles. Bibliographies of retrieved articles were examined for references of potential relevance. We included studies that described the use of ketamine for postoperative and emergency department management of pain and in the critically unwell, mechanically ventilated population. Results: There are few randomised controlled trials evaluating ketamine's utility in the ICU. The evidence is predominantly retrospective and observational in nature and the results are heterogeneous. Available evidence is summarised in a descriptive manner, with a division made between high dose and low dose ketamine. Ketamine's pharmacology and use as an analgesic agent outside of the ICU is briefly discussed, followed by evidence for use in the ICU setting, with particular emphasis on analgesia, sedation and intubation. Finally, data on adverse effects including delirium, coma, haemodynamic adverse effects, raised intracranial pressure, hypersalivation and laryngospasm are presented. Conclusions: Ketamine is used in mechanically ventilated ICU patients with several potentially positive clinical effects. However, it has a significant side effect profile, which may limit its use in these patients. The role of low dose ketamine infusion in mechanically ventilated ICU patients is not well studied and requires investigation in high quality, prospective randomised trials., Competing Interests: All authors declare that they do not have any potential conflict of interest in relation to this manuscript., (© 2022 College of Intensive Care Medicine of Australia and New Zealand.)