Background Delirium is common in elderly patients after surgery and is associated with poor outcomes. This study aimed to investigate the impact of intraoperative dexmedetomidine on the incidence of delirium in elderly patients undergoing major surgery. Methods This was a randomized double‐blind placebo‐controlled trial. Elderly patients (aged 60 years or more) scheduled to undergo major non‐cardiac surgery were randomized into two groups. Patients in the intervention group received a loading dose of dexmedetomidine 0·6 μg/kg 10 min before induction of anaesthesia followed by a continuous infusion (0·5 μg per kg per h) until 1 h before the end of surgery. Patients in the control group received volume‐matched normal saline in the same schedule. The primary outcome was the incidence of delirium during the first 5 days after surgery. Delirium was assessed with the Confusion Assessment Method (CAM) for non‐ventilated patients and CAM for the Intensive Care Unit for ventilated patients. Results In total, 309 patients who received dexmedetomidine and 310 control patients were included in the intention‐to‐treat analysis. The incidence of delirium within 5 days of surgery was lower with dexmedetomidine treatment: 5·5 per cent (17 of 309) versus 10·3 per cent (32 of 310) in the control group (relative risk (RR) 0·53, 95 per cent c.i. 0·30 to 0·94; P = 0·026). The overall incidence of complications at 30 days was also lower after dexmedetomidine (19·4 per cent (60 of 309) versus 26·1 per cent (81 of 310) for controls; RR 0·74, 0·55 to 0·99, P = 0·047). Conclusion Intraoperative dexmedetomidine halved the risk of delirium in the elderly after major non‐cardiac surgery. Registration number: ChiCTR‐IPR‐15007654 ( http://www.chictr.org.cn).

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Postoperative delirium (POD) is a complicated and harmful clinical syndrome. Traditional behaviour analysis mostly focuses on static parameters. However, animal behaviour is a bottom-up and hierarchical organizational structure composed of time-varying posture dynamics. Spontaneous and task-driven behaviours are used to conduct comprehensive profiling of behavioural data of various aspects of model animals. A machine-learning based method is used to assess the effect of dexmedetomidine. Fourteen statistically different spontaneous behaviours are used to distinguish the non-POD group from the POD group. In the task-driven behaviour, the non-POD group has greater deep versus shallow investigation preference, with no significant preference in the POD group. Hyperactive and hypoactive subtypes can be distinguished through pose evaluation. Dexmedetomidine at a dose of 25 μg kg−1 reduces the severity and incidence of POD. Here we propose a multi-scaled clustering analysis framework that includes pose, behaviour and action sequence evaluation. This may represent the hierarchical dynamics of delirium-like behaviours.