Using random case assignment to investigate the analgesic and sedative effect of intravenous dexmedetomidine and dexmedetomidine as a local anesthetic adjuvant in ultrasound-guided subcostal TAP block in gastric cancer patient undergoing gastrectomy or partial gastrectomy.

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.

Inclusion Criteria:

• gastric cancer patients undergoing gastrectomy or partial gastrectomy, who receive ultrasound-guided subcostal TAP block and PCA for postoperative analgesia

Exclusion Criteria:

• surgery involved other visceral organ (eg. combined splenectomy or partial hepatectomy), patients with histories of adverse drug reaction to dexmedetomidine, bradycardia (baseline heart rate <60 beats/min), any type of atrioventricular block in electrocardiogram (EKG), heart failure, significant renal or hepatic impairment, severe bronchopulmonary disease, any coagulant disorder, and pregnant or breast-feeding woman.