Optimal Dose of Dexmedetomidine for Preemptive Analgesia Combined with Transversus Abdominis Plane Block after Colon Cancer Surgery

Background: Pain after colon cancer surgery can be effectively relieved by transversus abdominis plane (TAP) block. We aimed to determine the optimal dose of dexmedetomidine for preemptive analgesia when combined with TAP block after colon cancer surgery. Methods: A total of 120 patients undergoing laparoscopic resection for colon cancer from March 2018 to October 2019 were randomly assigned to control (group C), low-dose (group L, 0.5 pg/kg), moderatedose (group M, 1 pg/kg), and high-dose groups (group H, 1.5 pg/kg) (n=30 each). After puncture under ultrasound guidance, the designated dexmedetomidine dose and 0.25% ropivacaine were injected on both sides (20 mL each side). Mean arterial pressure (MAP), heart rate (HR), numeric rating scale (NRS) score, and Ramsay score were compared at 2 h (T0), 4 h (T1), 8 h (T2), 12 h (T3), 24 h (T4), and 48 h (T5) after surgery. The area sensitive to mechanical stimulation-induced pain at the incision was measured at T4, T5, and 72 h after surgery (T6). Adverse reactions were compared.Results: MAP and HR were lower in the dexmedetomidine groups, especially groups M and H, than in group C (P<0.05). NRS scores at T0-T5 and pain-sensitive areas at T4-T6 were lower in the dexmedetomidine groups than in group C (P<0.05), but Ramsay scores were similar (P>0.05). Compared with group L, groups M and H had lower NRS scores and pain-sensitive areas (P<0.05). The incidence rates of adverse reactions were lower in the dexmedetomidine groups than in group C (P<0.05).Conclusions: Dexmedetomidine 1 or 1.5 pg/kg is effective and did not increase adverse reactions. A dose of 1 pg/kg is recommended as an adjuvant to ropivacaine for TAP block.