Abstract: Objective  To investigate the analgesic effect of erector spinae muscle block at different timings after thoracoscopic lobectomy and its impact on pulmonary function, serum pain factors, norepinephrine (NE) and prostaglandin E2 (PGE2). 
Methods  In this prospective randomized controlled study, a total of 88 patients undergoing thoracoscopic lobectomy in our hospital were assigned in a 1∶1 ratio to two groups, with 44 cases in each group. Both groups were given patient-controlled intravenous analgesia after surgery. The observation group was given ultrasound-guided unilateral erector spinae plane block before skin incision, and the control group was given ultrasound-guided unilateral erector spinae plane block after surgery. The visual analogue scale (VAS) pain scores at rest and during cough, pain factors ［5-hydroxytryptamine (5-HT), serum substance P (SP), neuropeptide Y(NPY)］, hemodynamics ［heart rate (HR), mean arterial pressure (MAP)］, NE, PGE2, percentage of predicted forced expiratory volume in 1 second (FEV1% pred), FEV1/forced vital capacity (FVC), and complications were compared between two groups. 
Results  There was no significant difference between VAS scores at rest and during cough immediately after extubation, and at 1 h, 6 h, 24 h, and 48 h after extubation in the two groups (P＞0.05). The comparison of 5-HT, SP, NPY immediately after extubation, at 6 h and 24 h after extubation between the two groups was not statistically significant (P＞0.05).HR and MAP immediately after extubation, at skin incision, and at 24 h after intubation were lower in the observation group than in the control group (P＜0.05); NE and PGE2 immediately after intubation, at skin incision and immediately after extubation in were lower in the observation group than in the control group (P＜0.05).FEV1% pred and FEV1/FVC at 48 h after extubation were higher in the observation group than in the control group (P＜0.05); the complication rate of the observation group (6.82%) was not significantly different from that of the control group (11.36%) (P＞0.05). 
Conclusion  Thoracoscopic lobectomy before skin incision and erector spinae muscle block after operation can effectively control pain, and the former has advantages in reducing stress response, maintaining hemodynamic stability, and improving early postoperative lung function, with good safety and reliability.

Key words: thoracoscopes, erector spinae, analgesia