Normobaric Hyperoxia Stabilizing Ischemic Penumbra

Inclusion criteria: * Age≥18岁 * The signs and symptoms are consistent with anterior circulation infarction, and baseline NIHSS score：6-20 * Level of consciousness on admission：0-1 * mRS score before stroke: 0-1 * Patients who did not receive revascularization therapy * The time from onset (finally normal) to randomization is less than 24h * Patients who signed informed consent * CTA or MRA confirmed internal carotid artery occlusion or M1/M2 segment occlusion of middle cerebral artery * The low-perfusion area with Tmax\>6s was larger than the core infarction, and the mismatch ratio was greater than or equal to 1.8. Exclusion Criteria: * Evidence of rapid improvement in neurological function and NIHSS score \<6, or spontaneous recanalization before randomization * The disease affecting assessment of baseline NIHSS score (dementia, epilepsy, neuromuscular disease, or psychiatric disease) * Symptoms suggesting subarachnoid hemorrhage (even if CT scan is normal) * Combined with the history, cerebral embolism due to sepsis or infective endocarditis was suspected * Active or chronic obstructive pulmonary disease, pulmonary fibrosis, pneumonia, pleural effusion, acute respiratory distress syndrome, irregular breathing * It is necessary to inhale (\>3L/min) oxygen to maintain peripheral arterial oxygen saturation (SaO2\>95%) * Anemia or polycythemia vera or other conditions needing emergency oxygen patients * Patients with upper gastrointestinal bleeding or nausea and vomiting can not complete inhalation oxygen using face mask * Baseline blood glucose \<2.78mmol/L or \>22.2mmol/L * Baseline platelet count \<50×109/L * Hereditary or acquired bleeding tendency, lack of coagulation factor, recent oral anticoagulant INR\>3 or PPT more than 3 times * Unstable vital signs (heart rate ≤50 beats/min or ≥120 beats/min, oxygen saturation ≤90%, R≥30 beats/min or ≤10 beats/min) * Hypertension not controlled by medication: systolic blood pressure ≥185mmHg, or diastolic blood pressure ≥110mmHg * Acute myocardial infarction suspected * Pregnancy, * Life expectancy \<90 days * Heart, liver and kidney failure * Magnetic resonance contraindications * Claustrophobia * Allergic to contrast media * Participating in other drug or device research