To investigate the safety and efficacy of normobaric hyperoxia (NBO) stabilizing penumbra in acute ischemic stroke patients.

All the enrolled patients were randomly assigned to NBO and control group. NBO group will be given 100% oxygen ( (10L/min for 4h) via a storage oxygen face mask and control group will be given oxygen using nasal oxygen(2L/min for 4h) .

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

Outcomes indexes will be assessed by trained neurologists or neuroradiologists who are blinded to the research content or patient grouping.