Background: Dexmedetomidine could be an ideal adjuvant to propofol during gastrointestinal endoscopy because it provides both analgesia and sedation without respiratory depression. This study investigates the effect of different doses of dexmedetomidine on the median effective concentration of propofol during gastrointestinal endoscopy. Methods: 90 adult patients were randomly assigned to Group Control , Group DEX0.5 (0.5 μg/kg dexmedetomidine), or Group DEX1.0 (1.0 μg/kg dexmedetomidine) . Anaesthesia during endoscopy was implemented by plasma target-controlled infusion (TCI) of propofol with different doses of dexmedetomidine. TCI concentration of the first patient for each group was 2.5 μg/ml and the consecutive adjacent concentration gradient was 0.5 μg/mL. EC50 of TCI propofol for gastrointestinal endoscopy was determined by using the modified Dixon’s up-and-down method. Cardiovascular variables were also measured. Results: EC50 of TCI propofol and 95% confidence interval (CI) for gastrointestinal endoscopy were, 3.77 (3.48-4.09), 2.51 (2.27-2.78) and 2.10 (1.90-2.33) μg/mL in Group Control, Group DEX0.5 and Group DEX1.0. The average percent change from baseline in HR was 2.8 (8.9), -7.4 (7.7) and -10.5 (8.8) (P＜0.001), and the average percent change from baseline in MAP was -10.6 [-24.7; 3.5], -9.5 [-29.2; 11.4] and -4.0 [-27.3; 15.5] (P = 0.034) in Group Control, Group DEX0.5 and Group DEX1.0, respectively. Conclusions: Dexmedetomidine reduced the EC50 of TCI propofol. A 0.5-1 μg/kg dexmedetomidine caused a decrease in HR without bradycardia. The decrease in dosage of propofol with increasing doses of dexmedetomidine caused more stable MAP. Dexmedetomidine is an ideal adjuvant drug to propofol during gastrointestinal endoscopy.

Abstract Background: Propofol may result in hypotension, bradycardia, and loss of protective reflexes, especially in elderly patients, while esketamine, a N-methyl-D-aspartate receptor antagonists, has analgesic, anaesthetic and sympathomimetic properties and is known to cause less cardiorespiratory depression. We hypothesized that esketamine may reduce the median effective concentration (EC50) of propofol and cause more stable haemodynamic responses during gastrointestinal endoscopy in elderly patients. Methods: Ninety elderly patients, aged 65-89 years, undergoing gastrointestinal endoscopy were randomly assigned into three groups: SK0.25 group (0.25 mg/kg esketamine), SK0.5 group (0.5 mg/kg esketamine) and saline control group. Anaesthesia was achieved by target-controlled infusion of propofol with an initial plasma concentration of 2.5 μg/ml with different bolus doses of esketamine during gastrointestinal endoscopy. The EC50 of propofol for gastrointestinal endoscopy was determined by using an up-and-down method of Dixon with an adjacent concentration gradient at 0.5μg/mL to prohibit purposeful movements. Cardiovascular parameters were also measured and recorded. Results: Propofol EC50 and its 95% confidence interval for gastrointestinal endoscopy in elderly patients were 1.71 (1.15-2.27) μg/mL in SK0.5 group, 2.45 (1.85-3.05) μg/mL in SK0.25 group and 3.69 (2.59-4.78) μg/mL in control group respectively (P < 0.05). The average percent change to baseline mean arterial pressure (MBP) was -19.7 (7.55), -15.2 (7.14) and -10.1 (6.73) with P＜0.001, in the control group, the SK0.25 group and the SK0.5 group, respectively. Conclusions: Combination medication of propofol with esketamine reduced the propofol EC50 during gastrointestinal endoscopy in elderly patients and caused more stable haemodynamic responses compared with single administration of propofol.