Stellate ganglion block (SGB) is known to increase blood flow to the innervation area of the stellate ganglion. Near infrared spectroscopy reflects changes of blood volume and allows continuous, non-invasive, and bedside monitoring of regional cerebral oxygen saturation (rSO2). Previous studies have shown the increment of the rSO2 on the block side from the baseline and the decrement of the rSO2 on the non-block side after SGB. Patients with cerebral vascular disease undergoing SGB might be at risk a decrease in cerebral blood flow in the non-block side. The investigators researched the effect of oxygen administration on rSO2 in the non-block side using a near infrared spectroscopy after SGB. 5 L/min oxygen was supplied via nasal cannula from 15 minutes after SGB. The rSO2 in the non-block side were measured before SGB and 5, 10, 15, 20, 25 and 30 minutes after SGB.