The effects of different doses of dexmedetomidine on the requirements for propofol for loss of consciousness in patients monitored via the bispectral index: a double-blind, placebo-controlled trial

BACKGROUND: The α(2)-adrenergic agonist dexmedetomidine (DEX) is a sedative and can be used as an adjunct to hypnotics. The study sought to evaluate the effects of different doses of DEX on the requirements for propofol for loss of consciousness (LOC) in patients monitored via the bispectral index (BIS). METHODS: In this randomized, double-blind, three arm parallel group design and placebo-controlled trial, 73 patients aged between 18 and ~ 65 years with a BMI range of 18.0–24.5 kg·m(− 2) and an American Society of Anesthesiologists (ASA) grade I or II who were scheduled for general anesthesia at the General Hospital of Ningxia Medical University were included in this study. Anesthesiologists and patients were blinded to the syringe contents. All patients were randomly assigned in a 1:1:1 ratio to receive a 0.5 μg·kg(− 1) DEX infusion (0.5 μg·kg(− 1) DEX group; n = 24), a 1.0 μg·kg(− 1) DEX infusion (1.0 μg·kg(− 1) DEX group; n = 25) or a saline infusion (control group; n = 24) for 10 min. Propofol at a concentration of 20 mg·kg(− 1)·h(− 1) was then infused at the end of the DEX or saline infusion. The propofol infusion was stopped when the patient being infused lost consciousness. The primary endpoint were propofol requirements for LOC and BIS value at LOC. RESULTS: The data from 73 patients were analyzed. The propofol requirements for LOC was reduced in the DEX groups compared with the control group (1.12 ± 0.33 mg·kg(− 1) for the 0.5 μg·kg(− 1) DEX group vs. 1.79 ± 0.39 mg·kg(− 1) for the control group; difference, 0.68 mg·kg(− 1) [95% CI, 0.49 to 0.87]; P = 0.0001) (0.77 ± 0.27 mg·kg(− 1) for the 1.0 μg·kg(− 1) DEX group vs. 1.79 ± 0.39 mg·kg(− 1) for the control group; difference, 1.02 mg·kg(− 1) [95% CI, 0.84 to 1.21]; P = 0.0001). The propofol requirements for LOC was lower in the 1.0 μg·kg(− 1) DEX group than the 0.5 μg·kg(− 1) DEX group (0.77 ± 0.27 mg·kg(− 1) vs. 1.12 ± 0.33 mg·kg(− 1), respectively; difference, 0.34 mg·kg(− 1) [95% CI, 0.16 to 0.54]; P = 0.003). At the time of LOC, the BIS value was higher in the DEX groups than in the control group (67.5 ± 3.5 for group 0.5 μg·kg(− 1) DEX vs. 60.5 ± 3.8 for the control group; difference, 7.04 [95% CI, 4.85 to 9.23]; P = 0.0001) (68.4 ± 4.1 for group 1.0 μg·kg(− 1) DEX vs. 60.5 ± 3.8 for the control group; difference, 7.58 [95% CI, 5.41 to 9.75]; P = 0.0001). CONCLUSION: The study showed that DEX (both 0.5 and 1.0 μg·kg(− 1) DEX) reduced the propofol requirements for LOC. DEX pre-administration increased the BIS value for LOC induced by propofol. CLINICAL TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov (trial ID: NCT02783846 on May 26, 2016).