Comparison of the Effect of Intravenous Continuous Dexmedetomidine Infusion and Dexmedetomidine as a Local Anesthetic Adjuvant in Subcostal Transverse Abdominis Plane Block in Patients Undergoing Gastric Cancer Surgery

The process of the experiment (brief describe) The participant patients will be randomly allocated into three groups: the intravenous dexmedetomidine group (Dex_iv group), dexmedetomidine adding to local anesthetic as an adjuvant for subcostal TAP block (Dex_adj group), and Control group. All patients receive gastrectomy or partial gastrectomy in general anesthesia as standard. Thirty minutes before the end of surgery, the patients in Dex_iv group receive 0.5mcg/kg dexmedetomidine infusion for 30 minutes, while the patients in Dex_adj group and control group receive 0.125ml/kg 0.9% normal saline IV infusion for 30 minutes. All patients have ultrasound-guided TAP block single injection after the end of surgery and before the tracheal tube extubation. The block agents in Dex_adj group is 40 ml of 0.375% ropivacaine with 0.5mcg/kg dexmedetomidine, while in Dex_iv group and control group are only 40ml of 0.375% ropivacaine. The IV PCA pump will be set up before patients awaken in the post-anesthesia care unit. All patients are assessed for the signs of emergence agitation with Riker sedation-agitation scale in the post-anesthesia care unit. The numerical rating scale (NRS) for pain intensity assessment, the opioid consumption via IV PCA pump, and the patients satisfaction will be documented for postoperative 3 days for the impact evaluation of dexmedetomidine in postoperative analgesia in patients undergoing gastric cancer surgery with subcostal TAP block.