Intracranial pressure is measured indirectly using optic nerve sheath diameter with ultrasound. It is reported that epidural pressure varies according to different posture ( lateral decubitus vs. sitting position).

This study is designed to measure the optic nerve sheath diameter in lateral decubitus and sitting position, respectively.

According to previous study, injection of different volume of local anesthetics (1.0 ml/kg vs. 1.5 ml/kg) during caudal anesthesia, high volume of local anesthetics resulted in significant increase of intracranial pressure (ICP). Increase of ICP can reduce regional cerebral flow and oxygen saturation causing the safety of patients. In addition, increase of ICP can result in headache, syncope, and transient loss of visual acuity. Although it is very invasive method, ICP can be measured directly at the brain parenchyme. Among methods to measure the ICP indirectly, measurement of optic nerve sheath diameter using ultrasound is known to reflect the degree of ICP. It is reported that optic nerve sheath diameter increases when higher volume of medication is injected during epidural anesthesia. Previous reports showed that epidural pressure varies according to different posture. When epidural pressure was measured in patients of spinal stenosis, lumbar flexion showed lower epidural pressure than epidural pressure of lumbar extension. In addition, when epidural pressure was measured in the sitting position, it showed lower pressure than pressure of lateral decubitus.

Inclusion Criteria:

• lung cancer
• liver cancer
• stomach cancer
• pancreas cancer

Exclusion Criteria:

• coagulopathy
• infection
• previous spine fusion at thoracic level
• previous brain surgery