Normobaric Oxygen in AIS Transferred for EVT

Inclusion Criteria:

1. Age at least 18 years old;

2. Signs and symptoms are consistent with a new acute stroke, with low possibility ofstroke mimics (e.g., no sudden coma, prior seizure disorder, suspectedhypoglycemia);

3. No prior stroke in the last 3 months;

4. Time from stroke onset (last seen well) to randomization is within 9 hours;

5. (1) Baseline NIHSS score at 6 or more and Intracranial ICA or MCA-M1 or MCA-M2dominant occlusion, with or without tandem cervical carotid stenosis or tandemcervical occlusion, confirmed by preoperative CTA (or MRA, DSA) and consistent withsigns and symptoms; or (2) Baseline NIHSS score at 6 or more with a hyperdense MCAsign on non-contrast CT; or (3) Baseline NIHSS score at 12 or more;

6. NIHSS score 0 or 1 in the section of level of consciousness;

7. No significant pre-stroke disability (pre-stroke mRS 0--1);

8. ASPECTS at least 6 on non-contrast CT;

9. Patient is planned for transfer to a EVT-capable hospital for EVT;

10. Signed informed consent from the patient or the legally authorized representative (LAR).

Exclusion Criteria:

1. Known history of severe chronic obstructive pulmonary disease (FEV1 less than 1.0),New York Heart Association (NYHA) Heart Failure Class III or IV, acute pulmonaryinfection or aspiration pneumonia, prior to enrollment;

2. Respiratory rate <= 10 or >= 30 breaths per minute;

3. Oxygen-dependence at baseline to maintain SaO2 > 95% or intubation at baseline;

4. Seizure at stroke onset;

5. Exhibiting symptoms of vomiting, or severe headache, or unconscious;

6. Rapidly improving neurological deficits or transient ischemic attack prior toconsent;

7. Signs and symptoms suggestive of subarachnoid hemorrhage, even if CT scan is normal;

8. Evidence of intracranial tumor (except small meningioma) or arteriovenousmalformation;

9. Woman of childbearing potential known to be pregnant or with a positive pregnancytest;

10. Life expectancy < 90 days due to comorbidity;

11. Unlikely to complete the 90-day follow-up;

12. Participating in another clinical treatment trial, or completed participation withinprior 30 days;

13. Receiving other cerebral protective agent (e.g., edaravone dexborneol,n-butylphthalide);

14. Evidence of acute intracranial hemorrhage on CT/MRI;

15. Significant mass effect with midline shift, defined as any deviation of midlinestructures such as the septum pellucidum, is observed on CT/MRI scans.