Commentary: ED50 and ED95 of hypobaric ropivacaine during unilateral spinal anesthesia in older patients undergoing hip replacement surgery

Lin et al. provided crucial clinical insights into dosage optimization for unilateral spinal anesthesia in older adults, a demographic vulnerable to anesthetic complications (1) . Although the authors utilized Dixon's sequential design, a methodologically apt approach for estimating median effective doses, a thorough examination of the reported dose-response parameters reveals a significant pharmacological inconsistency that warrants discussion for the accurate interpretation of the findings.In Table 2 and the Results section, the authors reported an ED50 of 11.13 mg (95% CI: 10.85-11.42 26 mg) and an ED95 of 10.30 mg (95% CI: 9.04 -10.65 mg). This result contradicts the established 27 pharmacological principles. By within any monotonic dose-response framework 28 (including and regression the dose needed to elicit a response 95% of the 29 population (ED95) must be greater than that for 50% (ED50) (2,3) . The reported inversion of these 30 values is mathematically unexpected and may suggest an underlying issue in the model specification 31 or interpretation.