A New Technique to Assist Epidural Needle Placement Fiberoptic-guided Insertion Using Two Wavelengths

Background: Up to 10% of epidurals fail due to incorrect catheter placement. We describe a novel optical method to assist epidural catheter insertion in a porcine model. Methods: Optical emissions were tested on ex vivo tissues from porcine paravertebral tissues to identify optical reflective spectra. The wavelengths of 650 and 532 nm differentiated epidural space from the ligamentum flavum. We then used a hollow stylet that contained optical fibers to place epidural needles in anesthetized pigs. Real-time data were displayed on an oscilloscope and stored for analysis. A total of 50 punctures were done in four laboratory pigs. Data were expressed as mean +/- SD. Results: Paired t test shows significant optical differences between the epidural space and the ligamentum flavum at both 650 nm (P < 0.001) and 532 nm (P = 0.014). Mean magnitudes for 650 nm, 532 nm, and their ratio were 3.565 +/- 0.194, 2.542 +/- 0.145, and 0.958 +/- 0.172 at epidural space and 3.842 +/- 0.191, 2.563 +/- 0.131, and 1.228 +/- 0.244 at ligamentum flavum, respectively. There were no differences in the optical characteristics of the ligamentum flavum and epidural space at different levels in the lumbar and thoracic region (two-way ANOVA P > 0.05). Conclusions: This is the first study to introduce a new optical method to localize epidural space in a porcine model. Epidural space could be identified by the changes in the reflective pattern of light emitted at 650 nm, which were specific for the ligamentum flavum and dural tissue. Real-time optical information successfully guided a modified Tuohy needle into the epidural space.