Effect of Low-Dose Esketamine Combined With Dexmedetomidine on the Incidence of Chronic Postsurgical Pain in Patients Undergoing Pancreatic Surgery

The goal of this clinical trial is to learn if low-dose esketamine combined with dexmedetomidine can reduce chronic pain after pancreatic surgery in adults. It will also learn about its safety. The main questions it aims to answer are: * Does low-dose esketamine combined with dexmedetomidine lower the number of participants who have chronic pain 3 months after pancreatic surgery? * What medical problems do participants have when receiving this treatment? Researchers will compare low-dose esketamine combined with dexmedetomidine to a control group (saline placebo during surgery and standard sufentanil patient-controlled intravenous analgesia after surgery) to see if the study treatment reduces chronic pain after pancreatic surgery. This is a two-center randomized controlled trial. About 450 adults will be enrolled and randomly assigned to the treatment group or the control group. Participants will: * Be adults aged 18 years or older, weigh at least 40 kg, and be scheduled for elective pancreatic surgery, including pancreaticoduodenectomy (Whipple procedure), pancreatectomy, or distal pancreatectomy. * Receive the study drugs or placebo during surgery and use a patient-controlled intravenous pain pump after surgery. * Be followed for up to 3 months after surgery to check for chronic pain.