Sensitivity and specificity of waveform analysis for assessing postoperative epidural function.

STUDY OBJECTIVES:To characterize the accuracy of epidural waveform analysis (EWA) in assessing the functionality of thoracic epidural catheters in the immediate postoperative period (primary objective), and to determine the inter-rater reliability between EWA waveform observers (secondary outcome). DESIGN:Single center, prospective diagnostic accuracy cohort study. SETTING:Post-anesthetic care unit of a university teaching hospital. PATIENTS:84 adult patients undergoing elective thoracic, gynecologic, vascular, urologic, or general surgery with preoperative placement of a thoracic epidural catheter for perioperative analgesia. INTERVENTIONS:EWA tracings were video recorded in the immediate postoperative period through the epidural catheter in the post-anesthetic care unit. MEASUREMENTS:Postoperative EWA tracings were compared with clinical assessments of the sensory block to ice produced by epidural local anesthetic in the immediate postoperative period. Additionally, intra-class correlation analysis of agreement between 3 independent (and blinded) EWA waveform observers was carried out. RESULTS:Among 80 patients with thoracic epidurals who completed the study protocol, 73 demonstrated postoperative functional epidurals with sensory block to ice and 7 demonstrated non-functional epidurals. EWA yielded 65 true positives, 6 true negatives, 8 false negatives, and 1 false positive. Postoperative EWA sensitivity, specificity, positive predictive value and negative predictive value, along with the 95% confidence intervals (CI) were 89% (79-95%), 86% (42-100%), 98% (92-100%), and 43% (18-71%) respectively. Intra-class correlation between waveform assessors was 0.870 (95% CI 0.818-0.910, p < 0.001). CONCLUSIONS:EWA is useful in assessing the position of thoracic epidural catheters in the immediate postoperative period, demonstrating high sensitivity and specificity as well as robust inter-rater reliability. For patients in whom sensory block to ice cannot be reliably assessed postoperatively, EWA may provide a useful adjunct for assessing epidural functionality.