The purpose of this study is to examine the hemodynamics of stroke patients with near-infrared spectroscopy before, during and after endovascular treatment and their relations to disabilities and mortality 3 months after treatment.

Endovascular treatment is the revascularization after ischemic stroke due to large-artery occlusion by mechanical removal of thrombi with an intraarterial catheter. The area around the infarction called the penumbra, which has partial blood supply by collateral vessels, can thereby be salvaged and the neuronal function restored. EVT lowers the disabilities and the morbidity if it is performed within 6 hours of onset or within 24 hours in stroke patients with a significant penumbra (Rodrigues, Neves et al. 2016).

However, complications can arise during EVT including critically failing CBF, intracranial hemorrhage and embolization of the thrombus to more peripheral vessels, which can all result in further brain damage.

To avoid these repercussions or detect them as fast as possible as well as detecting successful interventions, a suitable method for monitoring CBF over time is needed. NIRS is a commonly applied method that examines CBF in the cerebral cortex, which has already been used as intraoperative monitoring during abdominal and cardiac surgery (Yu, Zhang et al. 2018), but only in minor studies of EVT patients, where results have been very promising and associated to long-term outcomes (Hametner, Stanarcevic et al. 2015, Ritzenthaler, Cho et al. 2017). NIRS exploits that absorption of infrared light is only changed by hemoglobin, which can therefore by measured over time. NIRS is a non-invasive and safe method that measures oxygenated and deoxygenated hemoglobin in the cerebral cortex (Ferrari and Quaresima 2012).

Cerebral autoregulation (CA) is a complex mechanism that maintains an relatively constant and adequate CBF, which is often impaired in acute stroke patients (Paulson, Strandgaard et al. 1990). The nature of CA can be examined with NIRS (Obrig, Neufang et al. 2000, Reinhard, Wehrle-Wieland et al. 2006, Schytz, Hansson et al. 2010, Zweifel, Dias et al. 2014) and impairment can be shown (Li, Wang et al. 2010, Han, Li et al. 2014, Han, Zhang et al. 2014, Phillip and Schytz 2014). NIRS examinations of CA has never been done during EVT and the relation between changes in CA and patient outcome remains unknown.

This leads to the following hypothesis:

• CBF and CA can be monitored with NIRS before, during and after EVT and detect complications and successful EVTs.
• CBF and CA during and after EVT can be associated to the disabilities and mortality of stroke patients 3 months after the treatment.

The investigators will examine stroke patients who receive EVT with NIRS. The equipment will be placed on participants forehead when they arrive to the department and monitored for up to 2 hours after EVT. A 20-minute follow-up NIRS examinations will be done at 24 hours and 3 months after EVT. National Institute of Health Stroke Scale (NIHSS) will be performed before and after EVT, at 24 hours and 3 months after EVT. Participants will be assessed for functioning level and scored for independence with Modified Ranking Scale and screened for new vascular events, complications related to EVT and death by cause after 3 months.

To satisfy power calculations, 100 patients will be enrolled in the study.

Inclusion Criteria:

• Stroke patients receiving endovascular treatment

Exclusion Criteria:

• Premorbid mRS > 3
• Acute EEG examinations within 2 hours after EVT
• Neurosurgical evacuation within 2 hours after EVT
• Remaining life expectancy < 90 days

All patients who could be candidates for endovascular treatment in Region Zealand and The Capital Region of Denmark are assessed in Rigshospitalet, yearly around 200 patients. If endovascular treatment is attempted, subjects will be included. Only ischemic stroke patients with large-vessel occlusion will be eligible for endovascular treatment.

Only patients fulfilling the inclusion criteria and not the exclusion criteria are eligible. Patients will be enrolled before consent is given. Consent is obtained after endovascular treatment after oral and written information is provided. Recruitment is approved by Ethics Committee.