Comparison of the effect of dexmedetomidine intrathecal injection and intravenous infusion on subarachnoid blockade during knee arthroscopy procedures

Background: Comparison of whether intrathecal dexmedetomidine prolongs spinal anesthesia-associated sensorimotor blockade more than intravenous infusion during knee arthroscopy procedures performed under subarachnoid block. Methods: : Ninety patients aged 18-75 years, ASA class I-II, who underwent knee arthroscopy between October 2022 and April 2023 were randomized into intrathecal、intravenous and control groups.Subjects received three modes of administration: an intrathecal group (2ml of 1% ropivacaine + 5μg of dexmedetomidine，with saline pumped intravenously at a dose of 0.5μg/kg/h), an intravenous group (intrathecal 2ml of 1% ropivacaine +1ml of 0.9% saline, with dexmedetomidine pumped intravenously at a dose of 0.5μg/kg/h), and a control group (intrathecal 2ml of 1% ropivacaine + 1ml of 0.9% saline, with saline pumped intravenously at a dose of 0.5μg/kg/h). Total analgesic duration, duration of sensory and motor blockade, Ramsay sedation score, Visual Analogue Score (VAS) at different postoperative time points, and occurrence of adverse effects were recorded. Results: ：The total analgesia duration was significantly longer in the intrathecal group than in the intravenous and control groups (352.13±51.70min VS 273.47±62.57min VS 241.41±59.22min，P<0.001).The duration of sensory block was shorter in the intrathecal group than in the intravenous and control groups (4 [3-4]min VS 5 [4-5]min VS 5 [4-5]min；P<0.001);the duration of motor block was shorter in the intrathecal group than in the intravenous group and the control group (5 [4-5]min VS 5 [5-6]min VS 6[5.5-7]min；P<0.001).Sedation scores were higher in the intravenous group than in the intrathecal and control groups (P < 0.001). At 5 hours postoperatively, the VAS score in the intrathecal group was smaller than that in the intravenous and control groups (P<0.001). At 24 hours postoperatively, the VAS score in the intrathecal group was smaller than that in the control group (P < 0.001). In addition, the incidence of bradycardia was significantly higher in the intravenous group than in the intrathecal and control groups (30%, 6.5%, and 3.4%, respectively; P=0.018，P=0.007). Conclusions: ： Intrathecal administration of dexmedetomidine did prolong the total analgesia duration, as well as accelerate the onset of sensory-motor blockade compared with intravenous pumping, and did not result in any hemodynamic instability or other adverse events at the doses studied. Trial registration: This single-center, prospective, RCT has completed the registration of the Chinese Clinical Trial Center at 26/09/2023 with the registration number ChiCTR2300076170.