Delirium in ICU is frequent with harmful consequences for patients (22). EEG is a noninvasive, broadly available tool that can provide important information for delirium detection and management (23). According to our findings, presence of burst-suppression, rhythmic or periodic patterns, or epileptic activity, seem associated with a higher likelihood of delirium. Our data suggest that identification of these particular EEG patterns in patients with severe critical illness with altered consciousness state may be indicative of delirium. They support the concept that EEG monitoring is helpful in this setting, and if done at the early phase may prompt preventive or therapeutic anti-delirium strategies.
In our study, a small proportion of patients with delirium had burst-suppression during EEG. Sedation rates were similar in both groups before and during EEG, minimizing sedative drugs influence over EEG between both groups. Burst-suppression in ICU may be an independent predictor of delirium as previously suggested by another study using processed EEG (24), could primarily attributable to critical illness itself (25), and may be associated with increased mortality (26). We observed seizures and status epilepticus in 7% of our patients with delirium compared to none in the group without delirium. Seizures are known to be associated with a poor outcome in patients in ICU (27) and can be found in patients with delirium of any cause and in patients with sepsis like the majority of our patients (2, 28). The co-occurrence of seizures in septic patients may be seen as a potential marker of brain dysfunction with prognostic significance (2, 28, 29). On the other hand, presence of epileptiform activity may worsen and/or may even trigger delirium in some patients(30). Periodic discharges without seizures were also more prominent in delirium patients; studies in neurologic ICU patients suggest that periodic discharges are independent predictors of poor outcome (31, 32). Rhythmic or periodic patterns without seizure activity were significantly more prevalent in patients with delirium and are part of the ictal-interictal continuum (33). Individual management according to each pattern and close monitoring is advised for early detection and treatment of epileptiform activity if present (33, 34).
Generalized EEG slowing (increased delta and theta frequency) is frequently found in patients with delirium (9, 29). However slowing is also common in ICU patients and related with various causes of altered mental status, decreased arousal, including coma, sleep, and sedation(35). In our study, we did not find any significant differences in slowing when patients were compared for delirium. Triphasic waves evolve from an interplay of pathological neurostructural, metabolic, and toxic conditions, and are significantly associated with white matter disease, infections, and metabolic derangements (36). In our study, these were not increased in frequency in patients with delirium, as reported in previous studies (9, 37). NREM stage 1–2 sleep was not differently prevalent between the two groups It has been hypothesized that presence of sleep elements, especially K-complexes is associated with good outcome in encephalopathic adults (38) (39).
This study has limitations. The sample size is relatively limited and consisted of a selected population of non-neurological ICU patients, without acute brain injury. Data generalization is therefore limited. CAM-ICU scores were not available in all patients. EEG timing was not uniform across patients in relationship with their delirium development, but this reflects real clinical practice. Importantly however, clinical variables and EEG interpretation were completed prior to this analysis, and blinded to the development of delirium.