Background Effective postoperative analgesia is therefore critical for patients undergoing thoracoscopic surgery. Ultrasound-guided erector spinae plane block (ESPB) has demonstrated efficacy in reducing postoperative pain following thoracoscopic procedures; however, limited research exists regarding the minimum effective volume (MEV) of local anesthetic required. This study employed the biased coin up-and-down sequential method (BCD-UDM) to determine the MEV of 0.5% ropivacaine for ESPB in patients undergoing thoracoscopic lobectomy, thereby providing robust clinical data for optimizing analgesic protocols.

Methods ESPB was performed under ultrasound guidance using 0.5% ropivacaine hydrochloride. An initial volume of 26 mL was chosen. Utilizing the BCD-UDM, the volume administered to each subsequent patient was adjusted based on the analgesic efficacy observed in the previous patient. Specifically, if the prior patient did not achieve the predefined effective analgesia standard, the volume for the next patient was increased by 2 mL. Conversely, if the prior patient achieved effective analgesia, the subsequent volume was randomly reduced by 2 mL with an 11% probability, or left unchanged with an 89% probability. The study concluded upon reaching 45 successful block cases.

Results A total of 50 patients successfully completed the study. Ordinal regression analysis determined that the MEV90 of 0.5% ropivacaine for ESPB in postoperative analgesia following thoracoscopic lobectomy was 21.1 mL (95% CI, 21.00–22.75 mL). Further adjustment via the pooled adjacent violators algorithm (PAVA) indicated that an ideal volume of 24 mL is optimal for achieving effective analgesia.

Conclusion Our findings demonstrate that the MEV90 for 0.5% ropivacaine in ultrasound-guided ESPB for postoperative analgesia after thoracoscopic lobectomy is 21.1 mL (95% CI, 21.00–22.75 mL), with 24 mL representing the ideal volume for clinical application. These results provide valuable insights for optimizing postoperative pain management in thoracoscopic surgery.

The authors have declared no competing interest.

ChiCTR2400084646

The authors have no sources of funding to declare for this manuscript.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

This study was approved by the Ethics Committee of the First Affiliated Hospital of Dalian Medical University (Approval No. PJ-KS-KY-2023-429(X)).

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