"Diagnostic Accuracy of Ultrasound Compared to Epidurography for Epidural Catheter Localization in Patients Undergoing Open Abdominal Surgery"

Introduction

Major open abdominal surgeries often result in moderate to severe pain during the first 24-48 hours postoperatively. Epidural analgesia is effective in managing pain for open abdominal and thoracic surgeries during this immediate postoperative period and is considered the gold standard in accelerated rehabilitation protocols. The effectiveness of this pain relief method depends on the precise placement of the catheter in the epidural space. Since the procedure is performed blindly and relies on the anesthesiologist's skill, coupled with variations in anatomical structures, the failure rate of catheter placement ranges from 12% to 30%. Identifying catheter misplacement early in the postoperative period is challenging, as residual anesthetic effects may mask its ineffectiveness if the catheter is positioned outside the epidural space. This challenge can result in uncontrolled postoperative pain later on.

Given the inherent difficulties in catheter placement and the limitations of relying on indirect anatomical assessment and sensory cues, even experienced clinicians may find epidural catheter insertion challenging. Sensory testing and patient-reported pain scores, while useful, do not consistently offer objective confirmation of correct catheter placement. Therefore, more practical and objective methods are needed.

Ultrasound Techniques

Color Doppler ultrasound, which visualizes fluid dynamics and flow direction, and M-mode ultrasound, which provides grayscale images of movement, could offer valuable insights. When fluid is injected into a confined space like the epidural space, it is expected to create turbulence, which would appear as a burst of color on the Doppler image. This turbulence arises because the fluid encounters resistance as it moves through the narrow epidural space. Although studies have demonstrated the reliability of color Doppler ultrasound for visualizing fluid flow through a needle in the caudal space in both adults and children, this does not directly translate to assessing catheter placement in the lumbar epidural space. For example, case series by Riveros-Pérez et al. and Elsharkawy et al. reported that only 37% and 68% of epidural catheter tips were visible in the posterior complex using color Doppler, respectively. Studies have shown mixed results regarding their effectiveness, and their application to detecting catheter placement in the lumbar epidural space has yet to be fully established.