Five-day 20-minute 10-Hz tACS in Patients With a Disorder of Consciousness

Background: After a severe brain injury, a significant number of patients remain in a state of altered consciousness and the outcome remains difficult to prognosticate. There is a lack of evidence-based therapeutic interventions available for patients with disorders of consciousness; some evidence has been gathered for non-invasive brain stimulation, but these have targeted chronic patients. The objective of the validation phase will be to evaluate the differential feasibility parameters of conducting a 5-day tACS stimulation protocol in the ICU and the quality of data collection according to the various measurement modalities, to establish requirements to be used in a larger-scale study. This phase will also implicate a clinical pilot to confirm and assess the effect size of the primary outcome and sample size requirements for a clinical trial. Following completion, a clinical trial will be conducted to evaluate short-term and long-term neurophysiological effects of an optimized, multi-session tACS intervention in subacute brain-injured patients on their consciousness and functional recovery (as measured by complementary behavioural/functional scales), related brain oscillations and network dynamics.

Validation phase: In addition to conducting the following methods and design protocol, these measures will be acquired during the validation phase to assess the feasibility of this single-site study.

Recruitment rate and retention: Estimated number of patients in this condition in this ICU per year, estimated patient survival rates, number of eligible patients over a 12-month recruitment period; percentage of patients recruited, attrition, presence of competitive studies, etiologies and compliance of the families through experimental protocol and longitudinal assessment (12-month period).

Site demographics: Personnel's availabilities, Availability/accessibility of study coordinators, technicians, doctors and nurses; competency of the experimental team to conduct the experimental protocol.

Site infrastructure: Material storage (biological samples (centrifuge, freezer), Material obtention (Lidocaine obtention and renewal; EEG equipment), Data storage (clinically secure on-site servers).

Investigators' team requirements: Personnel requirements and the number of personnel required for the protocol's conductance.

Assessing the investigator's readiness in terms of standard care (eligibility decisions according to clinical profiles ), targeted study population and population recruited, and familiarity with the use of tools and technology.

Acceptability within the clinical care team's ecosystem: document pitfalls, difficulties and requirements to facilitate the clinical care team's adherence Quality of data collection: quality of EEG signal data in different clinical settings across main acquisition hospital sites; percentage of data acquisition completion; encountered data acquisition obstacles; assessment the estimated acquisition time for each measure and actual measuring times.

Methods/design:

The investigators will recruit brain-injured patients traumatic and non-traumatic etiologies (e.g., traumatic brain injury, anoxic brain injury, subarachnoid hemorrhage). Twelve patients will be recruited for the validation phase. The sample size estimation for the clinical trial based on a Student's t-test is 138 (2 groups of 69 patients) to reach a power of 80% to detect a statistically significant difference in the amplitude of alpha activity between active and sham groups, assuming a dropout/death rate of 20% and a significance level of 5%. These parameters are calculated according to a randomized, sham-controlled clinical trial comparing a 4-week tDCS protocol on patients with disorders of consciousness. The main outcome was a behavioral assessment, whereas this study's main outcome is neurophysiological, which is more sensitive to detect modulation effects. Additionally, this estimate will be readjusted according to the clinical pilot's results.

The study protocol will be activated once the medical team states clinical stability for the patients and withdrawal of continuous sedation has surpassed a minimum of 24 hours, without recovery of responsiveness.

Patients will participate in 7 consecutive experimental days including :

Day 0: Baseline measurements: Blood samples ( pharmacological agents dosage, the plasma expression of glial fibrillary acidic protein (GFAP) and isolation of exosomes derived from neurons (EDNs), astrocytes (EDAs) and microglia (EDMs)), Behavioral outcomes (Coma Recovery Scale-Revised (CRS-R), Glasgow Coma Scale (GCS) and Full Outline of Unresponsiveness (FOUR) Score) will be additionally measured for Unresponsive Wakefulness patients), pupillometry (photo motor reflex), and actigraph installation.

Days 1 to 5 (the following sequential procedure):

CRS-R/FOUR/GCS Pupillometry (PLR) 5-minute resting-state EEG 20-minute tACS/sham 5-minute resting-state EEG Pupillometry (PLR) CRS-R

5-minute resting-state 60-minute post-tACS condition/sham condition

5-minute resting-state 120-minute post-tACS condition/sham condition

Day 6:

CRS-R Pupillometry (PLR) 5-minute resting-state EEG

Day 7: After an interval of one-week post-5-day tACS/sham protocol, the following measurements will be acquired: CRS-R, Pupillometry (photo motor reflex), and 5-minute resting-state EEG. The actigraph will be withdrawn the during this same session.

At 3,6 and 12 months post-tACS, phone assessments will be conducted to measure long-term functional recovery using the following tools: Glasgow Outcome Scale- Extended, Disability Rating Scale, Functional Independence Measure and Burden Scale for Family Caregivers.