The Effect of Different Posture on Normal Saline Injection in Optic Nerve Sheath Diameter in Thoracic Epidural Anesthesia

Abstract

BACKGROUND Thoracolumbar or caudal epidural anesthesia affects intracranial pressure (ICP) in both animals and humans. Epidural injection increases ICP at least transiently. Measurement of the optic nerve sheath diameter (ONSD) using ultrasonography is one of the noninvasive methods for ICP assessment. OBJECTIVES The purpose of this study was to investigate the effect of the different posture during epidural saline injection to the ONSD under awake conditions. STUDY DESIGN Prospective, randomized trial. SETTING An interventional pain management practice in South Korea. METHODS This study included 44 patients receiving thoracic epidural catheterization for pain management after upper abdominal or thoracic surgery. Following successful epidural space confirmation, patients were randomized to receive epidural saline while supine (A group) or in sitting position (B group), respectively. Transorbital sonography was performed for the measurement of the ONSD, and the ONSD was measured at 3 mm posterior to the optic nerve head. RESULTS Both A and B groups showed significant increases of ONSD according to time. Mean ONSD values measured at T10, T20, and T40 significantly increased from the baseline value (T0) (*P < 0.05 vs. T0, †P < 0.001 vs. T0, ‡P < 0.005 vs. T0). The mean ONSD values measured at any of the time points and degrees of changes (T10-T0, T20-T0, and T40-T0) between groups A and B did not show any significant changes. LIMITATIONS Epidural pressure and ONSD measurement can make this study more reliable. Further study showing changes of epidural pressure with ONSD measurement is required. CONCLUSIONS Thoracic epidural injection of 10 mL of normal saline resulted in a significant increase of ONSD compared with the baseline. However, the different posture did not affect the increase of ONSD.