Mechanistic Evaluation of the Dural Puncture Epidural in a Porcine Model

Abstract

Background: The dural puncture epidural (DPE) technique involves placing a 17G Weiss needle in the epidural space, introducing a 25G Whitacre needle via the Weiss needle to puncture the dural sac, and threading a catheter into the epidural space. All medications are dosed through the epidural catheter.1 Compared to a conventional epidural (EPL) technique, the DPE has faster onset, greater bilateral and sacral coverage, fewer top-up requests, with no difference in rates of maternal hypotension, fetal bradycardia, high sensory block, or post-dural puncture headache.1-4 As radiographic evaluation of neuraxial techniques is limited to EPL techniques,5, 6 we conducted a fluoroscopy and necropsy porcine study to elucidate the mechanism, spread and distribution of EPL, DPE, and combined-spinal epidural (CSE) techniques. Methods: Following approval by our Animal Care and Use Committee, four 60 kg Yorkshire female pigs were sedated, intubated, and maintained with isoflurane in oxygen. Placed in the left lateral decubitus position, each pig had an attempted EPL, DPE, or CSE technique by a single operator at lumbar, low thoracic, or mid thoracic levels using a loss-of-resistance to air technique and fluoroscopy. Radio-opaque contrast (1 mL) was administered via the EPL catheter at 0, 45, 90, 135, and 180 min. Spread was assessed with fluoroscopy during injections. Dye (1 mL) was administered via the EPL catheter at 3 or 6 hours, the animals euthanized, and necropsy performed to assess dye distribution. Results: Ten experiments were conducted—consisting of EPL, DPE and CSE techniques, an inadvertent 17G dural puncture and a subcutaneous catheter placement. Fluoroscopic images demonstrated greatest to least segmental spread with CSE > DPE > EPL techniques throughout the 3-hr study period. Dye distribution was distinct to each technique (Table 1): With an EPL, dye was visualized only in the epidural space; DPE dye was visualized in both the epidural and subarachnoid spaces, though less than with a CSE at both 3 and 6 hrs. Conclusion: Our findings explain the clinical characteristics of the DPE technique: Dural sac puncture allows medication translocation from epidural to subarachnoid spaces for at least 6 hrs. This mechanistic understanding of the DPE, CSE, and EPL techniques offers insight into the procedural elements that ultimately contribute to the ideal neuraxial technique: one that provides rapid onset, reliable spread and quality, and titratable depth and duration, while balancing the risks of less desirable maternal and fetal outcomes.