Delirium is an acute disturbance of consciousness characterized by reduced orientation and impaired attention that cannot be explained by existing neurocognitive disorders or decreased consciousness [1]. Other cognitive functions may also be impaired, including language, memory, executive functioning, and perception. Delirium onset is relatively rapid with symptoms fluctuating throughout the day and night [2,3]. Symptomatology may vary according to delirium subtypes [4]. Hyperactive delirium is easily identifiable as it is characterized by increased psychomotor activity, including agitation, emotional lability, and hallucinations. Hypoactive delirium involves decreased psychomotor activity, including lethargy, decreased responsiveness, and slow motor skills. The subtle signs may delay recognition despite this subtype being quite prevalent in ICU patients. A third subtype involves mixed delirium which exhibits periods of agitation with periods of lethargy. The fluctuating nature makes it more challenging to categorize patients, requiring frequent and systematic assessment.

Precipitating factors of delirium include metabolic disturbances, pain, prolonged mechanical ventilation, respiratory failure, shock, immobility, sedatives, and conditions impairing hearing, sleep, and vision [[5], [6], [7], [8]]. Predisposing factors comprise hypertension, sepsis, cardiac disease, premorbid dementia, frailty and smoking [5,[9], [10], [11], [12]]. Most patients have both precipitating and predisposing factors [13,14]. The pathophysiologic basis of delirium has, however, yet to be fully elucidated.

In ICUs, delirium occurs frequently [15,16]. A recent systematic review and meta-analysis by Nan-Nan Wu et al. reported an incidence of 31 per 1000 ICU patients and a prevalence of 33 % [17]. Hypoactive delirium is most prevalent subtype accounting for 50.2 % of cases (95 % confidence interval [CI], 46.0–54.7), followed by mixed delirium with 27.7 % (95 % CI, 24.1–31.3), and hyperactive delirium being least prevalent with 22.7 % (95 % CI, 19.0–26.5) [4]. ICU delirium is associated with adverse outcomes including increased mortality, prolonged hospital stay, long-term cognitive impairment, and reduced quality-of-life after ICU discharge [5,[18], [19], [20]]. Despite the availability of adequate screening tools such as the Confusion Assessment Method for the ICU (CAM-ICU) and the Intensive Care Delirium Screening Checklist (ICDSC), delirium still often goes undiagnosed, and consequently, untreated [[21], [22], [23]].

Despite substantial research efforts to prevent ICU delirium, high certainty evidence remains scare, i.e., evidence for which further research is very unlikely to change our confidence in the estimated effects [24]. The potential to target different pathological pathways, plethora of potential interventions, both pharmacological and non-pharmacological, and heterogeneity in ICU patient delirium risk profiles, provide an abundance of research opportunities to expand the evidence-base for ICU delirium prevention.

This study aimed to gain expert consensus on topics considered as research priorities, thus informing the research agenda for the prevention of delirium in ICUs worldwide. An expert-endorsed research agenda may support a more focused allocation of resources for clinical researchers in intensive care.