Accuracy of EEG Slow Wave Activity in Predicting Favourable Outcome in Patients With Hypoxic Brain Injury - A Substudy of STEPCARE Trial

This is an observational substudy embedded in the STEPCARE Trial. The study involves EEG analysis, covered by the ethics approval of STEPCARE Trial. The investigators aim to compare the accuracy of a continuously measured algorithm-based EEG index, C-Trend Index, with retrospective visual analysis of continuous EEG in predicting favorable functional outcome in adult patients treated in intensive care units after out-of-hospital cardiac arrest. The primary hypothesis is that the accuracy of C-Trend Index has at least 10% better accuracy in predicting favorable outcome than the visual analysis of cEEG, when assessed early, 9-12 hours after return of spontaneous circulation (ROSC).

STEPCARE Trial (Clinical trials identifier:NCT05564754) includes adult out-of-hospital cardiac arrest (OHCA) patients, with sustained ROSC, who remain comatose after resuscitation. STEPCARE is a factorial Trial, where all participants are randomized regarding three different interventions (minimal or deep sedation, target mean arterial pressure 65mmHg or 85mmHg, temperature management with or without a device). Patients with suspected or confirmed intracerebral hemorrhage, trauma or hemorrhage as reasons of arrest, those previously randomized to STEPCARE and patients with allergy to adhesive material or skin injury in the frontal-temporal area will be excluded (the latter two specific to this substudy).

The investigators aim to assess whether a new, algorithm-based index derived from continuous EEG (cEEG) recording is superior to retrospective visual analysis of cEEG in predicting functional outcome after OHCA, assessed restrospectively from early phase recordings, using the best hour within the 9-12-hour time interval after ROSC.

The cEEG will be collected using a commercially available Brainstatus device in selected centers participating in the STEPCARE Trial. cEEG will be visible to clinical team in centers using cEEG in routine monitoring, but blinded for those who do not routinely monitor cEEG in OHCA patients. C-Trend Index is blinded to clinicians and researchers, and will be analyzed retrospectively, after the primary outcome has been collected of the last patient of this substudy.

The primary outcome of this substudy is the functional outcome 6 months after OHCA, defined as modified Rankin Scale score (dichotomized as favourable mRS 0-3, and unfavourable mRS 4-6), assessed by blinded outcome assessors.

The investigators will compare accuracy (with separate comparisons of sensitivity and specificity) of C-Trend Index 9-12 hours after ROSC with the visual assessment of cEEG. C-Trend Index above a predefined cut-off value 20 is defined as indicative of favorable outcome, while in the visual assessment continuous or nearly continuous normal-voltage background without abundant discharges is considered indicative of favorable outcome .

To demonstrate a 10% difference in the accuracy, a sample size of 271 patients is needed. To account for loss of patients due to early wake-up, loss of follow-up, and technical issues in recordings the investigators aim at recruiting 300 patients.

As secondary research questions the study will also assess:

* The predictive accuracy off C-Trend Index in predicting unfavorable functional outcome, compared with visual analysis of cEEG
* The predictive accuracy of C-Trend Index using cut-off values 50 and 80 at 9-12 hours from ROSC in predicting favorable and unfavorable functional outcome
* Whether the predictive ability or the optimal cut-off value of C-Trend Index in predicting favorable and unfavorable functional outcome is affected by the three different interventions of the STEPCARE study

Eligibility Criteria:
Inclusion Criteria:

* Age 18 years or older
* OHCA, with sustained ROSC
* Unconscious after ROSC
* No limitations to full life support
* Randomized to STEPCARE Trial in a participating center with Brainstatus device available

Exclusion Criteria:

* age \<18
* Previously randomized to STEPCARE
* Trauma or hemorrhage as the reasons for arrest
* Suspected or confirmed intracerebral hemorrhage
* Allergy to adhesive material
* Damaged skin at the frontal-temporal are preventing electrode attachment