Warming of mepivacaine prolonged the onset of epidural test dose

Purpose: Test dose of mcpivacaine in epidural anesthesia is commonly used to detect misplaced catheter. However, the optimal temperature of mepivacaine has not been determined. We investigated whether the warming of mepivacaine was associated with the onset time and spread of sensory blockade. Methods: Fifty-Two patients scheduled for upper abdominal surgery were enrolled in this single-blinded randomized clinical trial. After the epidural catheter placement, 1.5% mepivacaine 3 ml at 20° C (RT group) or 37°C (PH group) was injected. Hypesthesic onset time and sensory blockade, including hypesthesia and analgesia, at 10 minutes after the epidural injection were evaluated. The lowest non-invasive mean arterial pressure (MAP) during induction was recorded. Hypotension was defined as a MAP < 60 mmHg or a more than 30% MAP decrease from the baseline. Results: Onset time of hypesthesia was significantly longer in PH group than RT group (263 ± 108 seconds vs. 332 ± 108 seconds, P = 0.010), and was not associated with age or BMI.Warming of mepivacaine did not affect the dermatome spread 10 minutes after injection (Hypesthesia: 7.4 ± 2.4 vs. 7.1 ± 2.0 segments, P = 0.565, Analgesia: 2.0 ± 1.8 vs. 1.3 ± 1.6 segments, P - 0.189, respectively). Development of hypotension and the dose of vasopressors during induction were comparable between the groups. No patients developed neurological complications after surgery. Conclusions: We demonstrated that low dose of preheated mepivacaine resulted in prolonged onset time. Mepivacaine should not be warmed when administered as an epidural test dose.