Response to “Unequal Local Anesthetic Dosing and Surgical Heterogeneity: Considerations for Interpreting the ESPB–TEA Non-Inferiority Trial” [Response to Letter]

We thank Dr. Liu and Dr. Lu for their thoughtful commentary on our trial comparing continuous erector spinae plane block (ESPB) with thoracic epidural analgesia (TEA) after thoracotomy. 1 We appreciate the opportunity to address their methodological concerns and provide additional context for interpreting our findings.Dr. Liu and Lu note that we did not perform objective sensory block assessment and raise concerns about distinguishing interfascial block effects from systemic local anesthetic absorption, particularly given the higher ropivacaine exposure in the ESPB group.As acknowledged in our manuscript, sensory block levels were not assessed as a separate study measure.However, catheter placement was confirmed under imaging guidance with fluoroscopy for TEA and ultrasound for ESPB to ensure appropriate positioning.We recognize that the clinical effectiveness of ESPB remains controversial; volunteer studies have demonstrated limited anterior thoracic sensory changes, 2 and anatomical investigations have shown inconsistent ventral injectate spread following the block. 3We agree that incorporating dermatomal mapping in future trials would help distinguish the relative contributions of interfascial spread and systemic absorption.Regarding local anesthetic dosing, the higher volume in the ESPB arm is a necessary consequence of the technique itself, not a design limitation.Neuraxial blockade achieves direct access to spinal nerve roots with small volumes, whereas fascial plane blocks depend on volume-driven interfascial spread to reach target structures. 4,5The dosing regimens in both arms were consistent with published recommendations for each technique. 4,6Our trial was designed as a pragmatic effectiveness comparison of two techniques as applied in clinical practice, not a mechanistic efficacy trial.Concerning local anesthetic systemic toxicity risk, no clinical signs were observed during the study.We agree that pharmacokinetic monitoring is a valuable addition to future investigations of continuous ESPB, particularly given the higher cumulative local anesthetic exposure compared with neuraxial techniques.The authors correctly identify uneven distribution of surgical procedures between groups, with pneumonectomy more frequent in the TEA group at 33.3% versus 8.7% in the ESPB group.Randomization was performed without stratification by procedure type, and the observed imbalance likely represents a chance finding in a small sample, as is recognized to