Objective To compare the effects of intraspinal administration of different dosages of dexmedetomidine (DEX) on sedation, shivering, and early postoperative cognitive function of elderly patients.Methods Elderly patients with lower extremity surgery under intravertebral anesthesia were randomly divided into group L, group M, and group H, with 25 cases in each group.The patients were given intraspinal anesthesia, and 10 min later slowly injected with DEX 0.5μg/kg.Then, the group L, group M, and group H were injected with DEX at 0.2 μg/(kg·h), 0.4 μg/(kg·h), and 0.7 μg/(kg·h) for maintenance.All the three groups stopped injection 30 min before the end of the surgery.Ramsay score, BIS, MAP, and HR, shivering grade, and shivering rate of the three groups were compared before anesthesia (T0), at the time of injection (T1), and 10 min (T2), 20 min (T3), 30 min (T4), and 1 h (T5) after surgery.Simple Mental State Scale (MMSE) was used at 1d and 7d after the surgery to measure the preoperative and postoperative incidence rate of cognitive dysfunction.Results The Ramsay scores of the three groups at T2, T3, and T4 were significantly higher than those at T0 and T1 (P<0.05), and at the same time point, the Ramsay scores of the group M and group H were higher than those of the group L (P<0.05).The BIS values of the three groups at T2, T3, and T4 were significantly lower than those at T0 and T1 (P<0.05), and at the same time point, the BIS values of the group M and group H were lower than those of the group L (P<0.05).The MAP and HR of the three groups at T2, T3, and T4 were significantly lower than those at T0 and T1 (P<0.05), and at the same time point, the MAP and HR of the group M and group H were lower than those of the group L (P<0.05).The incidence rates of shivering of the group M and group H were significantly lower than that of the group L (P<0.05).At 7 d after the operation, the MMSE scores of the three groups were significantly lower compared with preoperation, but there was no statistically significant difference in the incidence rate of POCD.Conclusion Compare with preoperation, DEX shows a better sedative effect and prevents POCD and shivering in elderly patients with lower extremity surgery.DEX at 0.4 μg/(kg·h) is appropriate in clinical application.