Tramadol

An experienced anesthesiologist administered anesthesia. Spinal anesthesia was used for all the patients, and ropivacaine (AstraZeneca AB; 18–22 mg) was administered at the puncture site (L2–L3 or L3–L4 level). Postoperative analgesia was started immediately after the cesarean section, and PCIA was performed through a mechanical infusion pump. Three analgesia strategies were selected. The selection of different analgesic strategies is determined by the drug inventory (the supply of drugs varies at different time period), and patients were classified into three groups according to three analgesic regimens. The tramadol group (group T) received a mixture of tramadol (Sandoz [China] Pharmaceutical Co., Ltd.; 800 mg) with 0.9% normal saline at a dose volume of 200 mL, flurbiprofen axetil group (group TF) received a mixture of tramadol (800 mg) and flurbiprofen axetil (Teide Pharmaceutical Co., Ltd., Beijing, China; 200 mg) with 0.9% normal saline at a dose volume of 200 mL, and butorphanol group (group TB) received a combination of tramadol (800 mg) and butorphanol (Hengrui Pharmaceutical Co., Ltd., Jiangsu, China; 2 mg) with 0.9% normal saline at a dose volume of 200 mL for PCIA. The PCIA pump was designed to have a background infusion rate of 4.0 mL/hour and an additional dose of 1 mL with a lockout period of 15 minutes.