Ultrasonography of optic nerve sheath diameter shows a good level of diagnostic accuracy for detecting intracranial hypertension. The aim of this study is to evaluate the effect of epidural block on intracranial pressure in pediatric patients with cerebral palsy undergoing osteotomy of lower extremity. Forty patients, aged 4 years to 13 years, receiving epidural block before osteotomy will be divided into bolus group (n=20) and infusion group (n=20). Randomly selected patients of the bolus group are given 0.3 ml/kg bolus of 0.15% ripivacaine for epidural block. In contrast, patients in the infusion group are given 0.3 ml/kg/hr 0.15% ripivacaine for epidural block. The primary endpoint is the difference in the optic nerve sheath diameter after epidural block measured by optic nerve ultrasonography between groups.