The Effect of Normal Saline Injection Volumes on the Optic Nerve Sheath Diameter during Thoracic Epidural Analgesia

Abstract

BACKGROUND: Saline or local anesthetic injection into the epidural space increases intracranial pressure (ICP), at least transiently. Measurement of the optic nerve sheath diameter (ONSD) using ocular ultrasonography is one of the noninvasive methods for ICP assessment.

OBJECTIVES: The purpose of this study is to investigate the effects of the different volume on the ONSD and cerebral oxygen saturation (rSO2) during thoracic epidural saline injection under awake conditions.

STUDY DESIGN: Prospective randomized, controlled trial.

SETTING: An interventional pain management practice in South Korea.

METHODS: This study included 71 patients receiving thoracic epidural catheterization for pain management, following upper abdominal or thoracic surgery. Following successful epidural space confirmation, patients were randomly allocated to receive 5 mL (5 mL group), 10 mL (10 mL group), and 20 mL (20 mL group) of epidural normal saline. Transorbital sonography was performed to measure the ONSD. This was measured at 3 mm posterior to the optic nerve head. An rSO2 was measured using cerebral oximeter sensors.

RESULTS: All 3 groups showed significant increases of ONSD from 10 minutes to 40 minutes as compared to baseline (before procedure). Among the 3 groups, the 20 mL group demonstrated the most significantly increased ONSD, as compared to the 5 mL and 10 mL groups. At the 20 minute and 40 minute time points, the ONSD showed a volume-dependent increase (P = 0.0005, P = 0.014). All 3 groups showed the rSO2 to be distributed between 60~70% without any statistical difference.

LIMITATIONS: We could not determine the returning point of the normalized ONSD value.

CONCLUSION: Twenty milliliters of normal saline epidural injection resulted in a significant increase of ONSD, as compared to the 5 mL and 10 mL groups. Our results also indicate that an increase of ONSD occurs in accordance with the injected volume of normal saline.