Reducing the temperature of tissue or organs (hypothermia) produces a protective state, through multiple molecular mechanisms, against adverse effects that arise from disrupted organ blood flow, e.g. in acute ischemic stroke (AIS). AIS is often caused by a blood clot that occludes a brain artery which, in turn disrupts brain blood flow. In large vessel occlusions, the current standard includes mechanical thrombectomy (MT), a minimally-invasive procedure that aims at removing the clot via endovascular means. In this case, brain cooling can lead to protection (neuroprotection) not only from the adverse effects of stroke/ischemia itself, but also from complications arising from sudden re-opening of the blocked artery through primary treatment, MT. This potential complication of MT is called reperfusion injury.

In this first-in-human investigational deivce study, Hybernia Medical's endovascular brain cooling system will be applied in acute ischemic stroke patients undergoing MT. Post-MT, selective brain hypothermia will be induced and maintained over 30 minutes. Endpoints of this study include, clinical safety, device performance/usability, and clinical outcome.

Inclusion Criteria:

1. Age 18 to 89
2. Informed signed consent obtained from patient or legally authorized representative
3. Clinical symptoms consistent with acute ischemic stroke
4. Pre-stroke modified Rankin Scale (mRS) score 0-1
5. National Institute of Health Stroke Scale (NIHSS) ≥ 6
6. Alberta Stroke Program Early CT Score (ASPECTS) score 5-10
7. IV tissue plasminogen activator (tPA) or Tenecteplase (TNK) may be administered within 4.5h of last known well (LKW), if patient eligible
8. Mechanical thrombectomy (MT) treatment performed with arterial puncture within 24h of LKW.
9. Pre-MT catheter angiogram shows target occlusion in intracranial ICA, M1 MCA, or M2 MCA
10. End of MT catheter angiogram shows achievement of moderate-to-complete reperfusion (modified Treatment in Cerebral Ischemia score or mTICI 2a-3)

Exclusion Criteria:

1. Pre-MT CT or MRI shows acute intracranial hemorrhage.
2. Previous intracranial hemorrhage, AVM, neoplasm (except small meningioma), or vascular stent-implant
3. Coma or reduced level of consciousness prior to MT (NIHSS 1A>1)
4. Seizure between LKW and time of potential enrollment
5. Severe contrast allergy or absolute contraindication to iodinated contrast.
6. Hypersensitivity to cold, i.e., history of cold-sensitive antibodies, Raynaud syndrome, or hepatitis C
7. Hematocrit <33%
8. Severe known renal impairment, i.e., requires renal replacement therapy (dialysis).
9. Post-reperfusion investigational therapy cannot be started within 150 min following pre-treatment CT or MR imaging
10. Presumed septic embolism, suspicion of bacterial endocarditis.
11. Known pregnancy (in women with child-bearing potential)
12. Body weight < 40kg
13. Patient not willing and able to participate in follow-up visits to day 90.
14. Life expectancy <6 months due to pre-existing conditions such as severe heart or renal failure, cancer, etc.
15. Currently or within past 30 days participating in another investigational treatment study