OBJECTIVE: To probe into the application effect of different doses of dexmedetomidine combined with ropivacaine in knee arthroplasty in elderly patients. METHODS: Totally 78 elderly patients undergoing knee arthroplasty admitted into Fuyang People ’ s Hospital from Mar. 2019 to Dec. 2020 were selected and divided into observation group and control group via random number table

with 39 cases in each group

all the patients were given myotomy tube block before the induction of anesthesia

the observation group was given 0. 75 μg/kg of dexmedetomidine combined with 0. 25% of ropivacaine

while the control group was given 1. 0 μg/kg of dexmedetomidine combined with 0. 25% of ropivacaine

the intravenous inhalational anesthesia was adopted during surgery

and patient-controlled intravenous analgesia was used after surgery. The onset and duration of sensory blockade

hemodynamic conditions before and after blockade

pain and sedation at different time points after surgery were compared between two groups; the number of patient-controlled intravenous analgesia（ PCIA） presses

the time of myodynamia recovery and the occurrence of adverse drug reactions were recorded during 48 h after surgery.RESULTS: The differences in onset and duration of sensory block were not statistically significant between two groups（ P>0. 05）; at 1 h and 6 h after surgery

the SpO2 levels of observation group were significantly higher than those of the control group

with statistically significant differences（ P<0. 05）

the differences in HR and MAP levels were not statistically significant between two groups（ P>0. 05）; at 6 h

12 h

24 h and 48 h after surgery

the differences in VAS scores and Ramsay scores were not statistically significant between two groups（ P > 0. 05）. The recovery time of grade Ⅱ and grade Ⅲ muscle strength of the observation group were significantly shorter than those of the control group

with statistically significant differences（ P<0. 05）; during the 48 h after surgery

the difference in the number of PCIA presses was not statistically significant between two groups（ P > 0. 05）. During the analgesia period

no adverse drug reactions such as respiratory depression and excessive sedation occurred in both groups

the differences in the incidence of nausea and vomiting

hypotension and sinus bradycardia were not statistically significant between two groups（ P > 0. 05）. CONCLUSIONS: Compared with 1. 0 μg/kg of dexmedetomidine combined with ropivacaine

0. 75 μg/kg of dexmedetomidine combined with 0. 25% of ropivacaine had less effect on patients’ SpO2

which can shortened postoperative myodynamia recovery time

with better efficacy and safety.