The goal of this clinical trial is to learn if transcranial alternating current stimulation can shorten the duration of delirium in intensive care setting. The main question it aims to answer:

• Is it possible to shorten the duration of delirium with transcranial alternating current stimulation?

Researchers will compare experimental treatment to sham.

Participants will receive experimental or sham treatment on maximum of two days depending on their delirium status. Duration of delirium is recorded and reported as "days alive and free of delirium".

Delirium is an acute-onset brain dysfunction related to extensive surgery or critical illness that leads to altered mental status and cognitive deficits. Delirium is associated with an increased length of stay in the ICU, cost of care, excessive mortality, and long-term cognitive and functional impairment. Although numerous prophylactic methods have been proposed, currently, no pharmacological or non-pharmacological methods are clinically effective. Patients with delirium have altered electroencephalography (EEG) findings among which most important are general slowing of EEG frequencies and dysconnectivity. Faster EEG frequencies, especially alpha-, beta-, and gamma-bands, are correlated with higher cognitive functions, such as memory and orientation. Transcranial alternating current stimulation (TACS) is a novel, noninvasive brain stimulation technology that cab modulate EEG frequencies by entraining of endogenous brain oscillations in response to exogenous stimuli. TACS has been shown to improve episodic memory, orientation, and cholinergic dysfunction in patients with Alzheimer's disease. TACS also increases alpha and gamma frequencies in EEG, and an increase in these frequencies is associated with the improvement of clinical symptoms. TACS has been shown to target key components of delirium pathophysiology, such as slowing of EEG frequencies and cholinergic dysfunction. Thus, we hypothesized that TACS could shorten the duration of delirium and decrease cognitive decline. We aim to test this hypothesis in a double-blind randomized trial and assess the effect of TACS on duration of delirium, EEG, biomarkers and long-term cognition.

Inclusion Criteria:

• Delirium in intensive care and duration of delirium for more than 24 hours. Delirium is defined as 4 or more points on ICDSC and -1 or more points on RASS.

Exclusion Criteria:

• Under 18 years of age, pregnancy, delirium tremens, epilepsy or history of seizures any time before first trial intervention, active psychotic disease, infection of central nervous system, acute intoxication, traumatic brain injury, stroke, intracranial bleeding and implanted electronic devices.