Diagnostic accuracy of the swirl sign for epidural catheter confirmation: A randomized pilot diagnostic evaluation

Study objective To evaluate the diagnostic accuracy and feasibility of the swirl sign, a novel bedside visual adjunct, for confirmation of epidural catheter placement. Design Prospective, randomized, parallel-group pilot diagnostic study. Setting Single tertiary-care teaching hospital. Patients Adult patients (18–65 years) with American Society of Anesthesiologists physical status I–III undergoing elective lower abdominal or lower limb surgery under combined spinal–epidural anesthesia. Intervention Patients were randomized to epidural catheter confirmation using the swirl sign combined with a conventional test dose (swirl group) or test dose alone (control group). Measurements The primary outcome was successful epidural block, defined as achievement of bilateral sensory block to T10 within 20 min without catheter reinsertion. Successful clinical block served as the pragmatic reference standard for diagnostic accuracy analysis. Secondary outcomes included diagnostic accuracy of the swirl sign (sensitivity, specificity, predictive values), onset time of analgesia, need for catheter reinsertion, and interobserver agreement for swirl sign interpretation. Main results A total of 180 patients were randomized (90 per group). Successful epidural block occurred in 94.4% of patients in the swirl group and 89.4% in the control group ( p = 0.21). Time to onset of T10 sensory block was shorter in the swirl group (11.2 ± 2.3 vs 12.1 ± 2.6 min; p = 0.03). The swirl sign demonstrated a sensitivity of 96.6%, specificity of 80.0%, positive predictive value of 98.9%, and negative predictive value of 57.1% when compared with successful clinical block as the reference standard. Interobserver agreement for swirl sign interpretation was excellent (κ = 0.84). No serious complications were observed. Conclusion The swirl sign is a feasible and highly sensitive bedside adjunct for epidural catheter confirmation, with excellent interobserver reproducibility. It did not significantly alter overall block success rates and should be considered an adjunctive diagnostic indicator rather than a replacement for standard confirmation methods. As an initial evaluation, this randomized pilot study supports further validation of the swirl sign in larger and multicenter settings.