Inclusion Criteria:  Age ≥20 years Anterior circulation progressive lacunar infarction. Neurological worsening either 1 point in NIHSS score or MRC grade  Exclusion Criteria:  Age <20 Cortical infarction Posterior circulation lacunar infarction Relevant artery stenosis more than 50% or occlusion Moyamoya disease Difficulty in inhalation of Carbogen (panic, severe anxiety disorder) Drug allergy for phenylephrine Persistent bradycardia (pulse rate < 50 /min) History of hemorrhagic stroke Pre-stroke mRS ≥2