The current endovascular treatment has increased the recanalization rate to more than 90%. Even so, the prognosis rate of stroke is still less than 50%. Our previous research confirmed that the neuroprotective effect of Normobaric Hyperoxia (NBO) from multiple perspectives. However, the clinical study on NBO was not satisfactory, which might be due to the absence of vascular recanalization therapy. Therefore, The investigators conducted this RCT study to further explore the Efficacy and safety of NBO combined with endovascular treatment in patients with acute ischemic stroke.

Inclusion Criteria:

General inclusion criteria

1. It conforms to the indications for endovascular thrombectomy
2. 18 ≦ Age ≦ 80 years old.
3. The clinical symptoms and signs are consistent with acute anterior circulation large vessel occlusion; 10≤NIHSS≤20；
4. (Level of consciousness) NIHSS score 0 or 1;
5. The time from onset to randomization is within 6 hours of onset;
6. The mRS score before stroke is 0-1;
7. Patient and family members sign informed consent. Image inclusion criteria

1. Preoperative CT or MR or DSA angiography found large vessel occlusion (internal carotid artery or middle cerebral artery M1 segment) that were consistent with symptoms and signs; 2. ASPECT score ≥ 6 points 3. <1/3 MCA area involvement (confirmed by CT or MRI)

Exclusion Criteria:

• General exclusion criteria

  1. Rapid neurological function improvement, NIHSS score less than 10 points, or evidence of vessel recanalization prior to randomization;
  2. Seizures at stroke onset;
  3. Intracranial hemorrhage;
  4. Symptoms suggestive of subarachnoid hemorrhage, even if CT scan was normal;
  5. Known hemorrhagic diathesis, coagulation factor deficiency, or on anticoagulant therapy with INR > 3.0 or PTT > 3 times normal;
  6. Platelet count of less than 100,000 per cubic millimeter;
  7. Severe hepatic or renal dysfunction;
  8. Severe, sustained hypertension (Systolic Blood Pressure >185 mmHg or Diastolic Blood Pressure >110 mmHg)
  9. Baseline blood glucose of <50mg/dL (2.78 mmol) or >400mg/dL (22.20 mmol)
  10. Active and chronic obstructive pulmonary disease or acute respiratory distress syndrome;
  11. >3 L/min oxygen required to maintain peripheral arterial oxygen saturation (SaO2) 95% as per current stroke management guidelines;
  12. Medically unstable;
  13. Life expectancy<90 days;
  14. Patients who could not complete the 90-day follow-up;
  15. Evidence of intracranial tumor;
  16. Patients with anemia or polycythemia vera or other situations that require urgent oxygen inhalation;
  17. Patients with upper gastrointestinal bleeding or nausea or vomiting so that they cannot cooperate with the mask to inhale oxygen.
  18. A history of severe allergies to contrast agents;
  19. There are any other conditions that are not suitable for endovascular treatment.

Image exclusion criteria

1. CTA/MRAshows excessive bending of blood vessels, which may hinder the delivery of the device;
2. Suspected cerebrovascular inflammation based on medical history and CTA/MRA;
3. Suspected aortic dissection based on medical history and CTA/MRA
4. CTA/MRA confirmed multi-vascular area occlusion (such as bilateral anterior circulation or anterior/posterior circulation), or bilateral infarction or multi- regional infarction;
5. CTA/MRAconfirmed moyamoya disease or moyamoya syndrome;
6. CT/MRI confirmed the obvious effect of midline shift
7. CT/MRI confirmed the presence of intracranial tumors