The primary purpose of this study is to explore the feasibility and safety of normobaric oxygen therapy (NBO) under pre-hospital condition in patients with suspected stroke.

Despite the application of thrombolytic drugs and endovascular treatment, there is still a gap between the successful recanalization and ideal clinical outcomes for stroke patients. Neuroprotective treatment is considered as a promising adjuvant to ameliorate this situation. Previous researches demonstrated the neuroprotective effects of Normobaric Hyperoxia (NBO) in animal models from multiple perspectives. Moreover, NBO is distinctive for its ubiquity, conveniency, high compatibility, and wide adaptability, making it superior to other neuroprotective interventions in a pre-hospital setting. Therefore, the investigators conducted this pilot study to further explore the feasibility and safety of NBO under a pre-hospital condition in patients with suspected stroke.

Inclusion Criteria:

1. Age 18 years or more.
2. Suspected stroke screened by the "Gaze- Face Arm Speech Time" scale (G-FAST score ≥ 1).
3. Within 24 hours of symptom onset
4. SpO2 > 94%.

Exclusion Criteria:

1. Coma: Glasgow coma score (GCS) < 8.
2. Hypoglycemia: Blood glucose < 2.8mmol /L.
3. Known history of seizure.
4. Recent stroke or brain trauma within past 30 days.
5. Previous Modified Rankin Scale (mRS) ≥2.
6. Rapid improvement of neurological dysfunction (deficit present less than 15 min).
7. Unstable vital signs.
8. Known respiratory distress, respiratory dysfunction, or any contraindications to high-flow oxygen inhalation therapy.
9. Patient unable to cooperate with the trial procedure.
10. Any condition which might increase the risk to the patient in the judgment of the investigator.
11. Patient or available legally authorized representative unable to provide written or witnessed oral consent.