Abstract:Objective To compare the postoperative analgesic efficacy of the in-plane versus out-of-plane approach for ultrasound-guided thoracic paravertebral block (TPVB) in patients undergoing thoracoscopic lobectomy. Methods A total of 102 patients scheduled for elective thoracoscopic lobectomy at Qilu Second Hospital of Shandong University from January to August 2025 were enrolled and randomly divided into an in-plane group (IP group, n=51) and an out-of-plane group (OOP group, n=51). All patients received a single-shot ultrasound-guided TPVB in the anesthesia preparation room before surgery. The primary outcome measure was the Visual Analogue Scale (VAS) score at 6 hours postoperatively. Secondary outcomes included cough VAS scores at 1, 2, 12, and 24 hours postoperatively, area under the curve (AUC) of VAS 24 hours postoperatively block performance time, needling depth, block onset and fixation time, extent of sensory block, intraoperative opioid consumption, patient satisfaction, and adverse reactions. Multivariate linear regression was used to analyze factors influencing the VAS-AUC at 24 hours postoperatively. Results There was no statistically significant difference between the two groups in VAS scores at various postoperative time points, 24-hour VAS-AUC, intraoperative opioid consumption, patient satisfaction, or incidence of intraoperative adverse reactions (P> 0.05). Compared with the IP group, the OOP group had a significantly shorter block performance time［194.00 (181.00, 217.00) s vs 227.00 (201.00, 259.50) s, Z=4.803, P<0.01］and shallower needling depth［2.80 (2.30, 3.40) cm vs 3.50 (3.00, 4.00) m, Z=4.854, P<0.01］. Multivariate linear regression analysis showed that sensory block extent, block onset time, and age were independent influencing factors of postoperative pain (P<0.05). Conclusion For thoracoscopic lobectomy, the out-of-plane approach for ultrasound-guided TPVB provides comparable postoperative analgesia to the in-plane approach, while offering the advantages of being more convenient to perform and requiring a shallower needling depth. The extent of sensory block, onset time block, and patient age are key factors influencing the analgesic efficacy of the out-of-plane TPVB approach.