A Study to Reduce Persistent Post-mastectomy Pain Using Opioid-free Anesthesia

Study population 1. All of patients will undergo mastectomy with or without immediate breast reconstruction. 2. 230 patients will be enrolled. Intervention 1. OFA group will be sedated using dexmedetomidine and lidocaine. 2. Conventional opioid anesthesia group will be sedated using remifentanil. Pain screening 1. Breast Cancer Pain Questionnaire (BCPQ) 2. Pain-detect, HADS, EQ-5D, PHQ-15 (somatic symptom), PCS (pain catastrophizing), BFI (big five inventory), HAM-A\&D, Pressure algometry (Pain sensitivity), Quantitative sensory test (pinprick)