Unequal Local Anesthetic Dosing and Surgical Heterogeneity: Considerations for Interpreting the ESPB–TEA Non-Inferiority Trial Letter

We read with interest the trial by Cho et al reporting non-inferiority of continuous erector spinae plane block (ESPB) versus thoracic epidural analgesia (TEA) after thoracotomy. 1 The study is carefully conducted, and the Bayesian complementary analysis strengthens its conclusions. We nevertheless wish to raise four methodological concerns that bear on the interpretation of the results. First, the study did not verify ESPB efficacy through objective sensory block assessment. Volunteer studies have shown that ESPB often produces only cutaneous posterior thoracic sensory loss with limited anterior spread, 2,3 making it difficult to determine whether analgesia in this trial reflected true interfascial block or systemic local anesthetic (LA) absorption. This question is particularly pressing given the large difference in LA dosing between arms: the ESPB group received a 20 mL pre-incision bolus, a 10 mL intraoperative top-up, and a 10 mL/h basal infusion, compared with 10 mL pre-incision and 3 mL/h in the TEA group. Over 72 hours, this translated into substantially higher total ropivacaine exposure in the ESPB group, with no plasma concentration monitoring or formal assessment of local anesthetic systemic toxicity (LAST) risk. 4,5 Future trials should include standardized dermatomal mapping prior to incision, dose-equivalent protocols, or pharmacokinetic monitoring to separate block-specific from systemic analgesic effects. Second,