BackgroundDexmedetomidine could provide some advantages to prevent postoperative complications in elderly patients undergoing under general anaesthesia. However, dexmedetomidine inhibits haemodynamics to some extent due to its sympathetic inhibition.ObjectiveTo evaluate the effects of different doses of dexmedetomidine on haemodynamics during surgery and recovery after general anaesthesia in elderly patients undergoing hip replacement.MethodsThis was a prospective randomized double-blind controlled clinical trial. Eligible patients were randomly allocated into comparative groups (normal saline (NS) and midazolam (MD),n= 30) and dexmedetomidine groups at different doses (D0.25/D0.5/D0.75,n= 30). In the D0.25/D0.5/D0.75 groups, dexmedetomidine was administered at different initial loading doses (0.25/0.5/0.75 μg/kg for 15 min) following 0.5 μg/kg/h continuous infusion until the end of the operation. In the MD group, patients were administered 0.03 mg/kg midazolam at the beginning of anaesthesia induction.ResultsCompared to the MD and NS groups, there were significant decreases in MAP in the D0.5 and D0.75 groups at many time points, such as skin incision, end of operation, and from extubation until 30 min after extubation (P< 0.05); there were also significant decreases in HR in the D0.5 and D0.75 groups at time points including anaesthesia induction, end of operation, and from extubation to 2 h after operation (P< 0.05). In the D0.25 group, there were few differences in the changes in MAP and HR compared to the MD and NS groups during the entire perioperative period (P> 0.05). Moreover, the percentage of patients whose MAP and HR decreased > 20% of baseline was higher in the D0.75 and D0.5 groups than that in all other groups. Compared to the NS group, from the beginning to the end of the operation, the 95% confidence interval (CI) of RR for MAP below > 20% of baseline in the D0.5 and D0.75 groups was greater than 1. In particular, the CI of the RR in the D0.75 group was greater than 1 until the patient awoke from general anaesthesia (P< 0.05). In addition, the CI of the RR for HR below > 20% of baseline in the D0.5 group was greater than 1 compared to the NS group at the time of induction and extubation (P< 0.05). There was no significant difference in the possibility of developing hypotension or bradycardia in the MD or D0.25 groups compared to the NS group (P> 0.05). The recovery quality of patients during the post-anaesthesia period was also observed. No differences were observed among all the groups in the time to awakening or extubation after general anaesthesia (P> 0.05). According to the Riker Sedation-agitated Scale, dexmedetomidine significantly alleviated emergency agitation or delirium compared to NS (P< 0.05). In addition, the scores in the D0.5 and D0.75 groups were lower than those in the D0.25 group (P< 0.05).ConclusionDexmedetomidine could alleviate the agitation of elderly patients undergoing hip replacement after intravenous general anaesthesia combined with inhaled sevoflurane without delayed recovery. However, it is necessary to be vigilant about the haemodynamic inhibition of the drug at high dosages throughout the perioperative period. Dexmedetomidine 0.25–0.5 μg/kg as the initial loading dose followed by 0.5 μg/kg/h continuous infusion might provide comfortable recovery after general anaesthesia with slight haemodynamic inhibition.Trail registrationClinicalTrial.gov, No. NCT05567523. Registered 05 October 2022,https://clinicaltrials.gov/ct2/show/NCT05567523?term=NCT05567523&draw=2&rank=1.