Fluoroscopically Guided Thoracic Interlaminar Epidural Injection: A Comparative Epidurography Study Using 2.5 mL and 5 mL of Contrast Dye

Background: Thoracic epidural anesthesia (TEA) is frequently used to maintain intraoperative analgesia. After injecting the initial bolus dose of epidural local anesthetics (LA), intermittent injection of LA through an epidural catheter is required to maintain the intraoperative analgesia. For intermittent epidural administration, usually 2 - 5 mL of LA has been used. However, no studies have suggested an optimal volume of LA of TEA for intermittent epidural administration of TEA. Objective: We focused on identifying an optimal volume of LA of TEA using epidurography of the thoracic level with 2 different volumes of contrast dye. Study Design: Prospective, randomized study. Setting: An interventional pain management practice in South Korea. Methods: After Institutional Review Board approval, 70 patients undergoing thoracic epidural catheterization for upper abdominal and thoracic surgery were randomly assigned to one of the 2 contrast dye volume groups of 35 patients each (A, 2.5 mL and B, 5.0 mL). Epidurography was evaluated to confirm how many spinal segments were covered by contrast dye. The spreads in the cephalad and caudad directions were also evaluated. Results: The total number of vertebral segments evaluated by contrast dye were 7.5 +/- 2.0, and 8.4 +/- 2.6, respectively in groups A and B. The number of patients who showed contrast dye spread of more than 5 vertebral segments was 34/35 (97%) in both groups. Group B resulted in higher contrast dye distribution in the cephalad direction compared to group A (T2.6 vs. T3.6). Limitations: We used a test dose of contrast dye to confirm the contrast was in epidural space, not intrathecal or vascular, before injection of the main dose of contrast dye. The present study did not include the volume of test dose. Conclusion: The volume of 2.5 mL for intermittent epidural administration would be enough for the analgesic effect of upper abdominal and thoracic surgery while avoiding excessive upper thoracic and cervical spread.