The purpose of this study is to evaluate the safety and efficiency of normobaric hyperoxia combined with endovascular treatment for acute ischemic stroke patients with stroke onset 6-24 hours.

Inclusion Criteria:

• age≥18;
• Suspected lage vessel occlusion of acute anterior circulation occlusion; i.e. either the ICA or the M1/M2-segment of the MCA;
• Stroke symptom onset has been more than 6 hours but not more than 24 hours,and imaging confirmed the existenceof ischemic penumbra;
• NIHSS score≥6;
• Alberta Stroke Program Early CT score (ASPECTS) of 6-10 on non- contrast CT;
• (Level of consciousness) NIHSS score of 0 or 1
• mRS score was 0-1 before stroke;
• Informed consent obtained;

Exclusion Criteria:

• Rapid improvement in neurological status to an NIHSS < 6 or evidence of vessel recanalization prior to randomization;
• Seizures at stroke onset;
• Intracranial hemorrhage;
• Systolic pressure greater than 185 mm Hg or diastolic pressure greater than 110 mm Hg, or aggressive treatment intravenous medication)necessary to reduce blood pressure to these limits;
• Symptoms rapidly improving;
• Symptoms suggestive of subarachnoid hemorrhage, even if CT scan was normal;
• Platelet count of less than 100,000 per cubic millimeter;
• CT showed a multiple infarction (low density area greater than 1/3 cerebral hemisphere);
• severe hepatic or renal dysfunction;
• active and chronic obstructive pulmonary disease or acute respiratory distress syndrome;
• >3 L/min oxygen required to maintain peripheral arterial oxygen saturation (SaO2)#95% as per current stroke management guidelines;
• medically unstable;
• inability to obtain informed consent;
• Life expectancy<90 days;
• Pregnant or breast-feeding women;
• Unwilling to be followed up or poor compliance for treatment;
• Patients being enrolled or having been enrolled in other clinical trial within 3 months prior to this clinical trial;
• Evidence of intracranial tumor;
• Baseline blood glucose of < 50 mg/dL (2.78 mmol) or > 400 mg/dL (22.20 mmol);
• Patients with upper gastrointestinal bleeding or nausea and vomiting who cannot use oxygen masks;
• Other circumstances requiring emergency oxygen inhalation;