General anesthesia is a medically induced state of low reactivity consciousness which is similar to natural sleep. Some studies found that general anesthesia as an independent risk factor could result in a desynchronization of the circadian time structure and cause postoperative sleep disorders characterized by reduced rapid eye movement (REM) and slow wave sleep (SWS), which have significant deleterious impacts on postoperative outcomes, such as postoperative fatigue, severe anxiety and depression, emotional detachment and delirium, and even pain sensitivity or postoperative pain of patients.Clinical trials have already proved that intraoperative use of dexmedetomidine (DEX) for general anesthesia, a highly selective alpha-2 adrenergic agonist, was able to improve sedative and analgesia effects and promote sleep quality (by decreasing stage N1 sleep, increasing stage N2 sleep and sleep efficiency). However, Wenfei Tan et al reported that with the deeper sedative state provided by DEX in the daytime, the elderly male patients undergoing TURP under spinal anesthesia suffered worse sleep on the night of surgery. Thus, what the effect of intraoperative using DEX at different time periods under general anesthesia on postoperative sleep quality and pain will be needs further study.

patients scheduled for elective laparoscopic abdominal surgeries under general anesthesia were enrolled. Patients were randomized to receive operation in the D group (8:00-12:00) and the N group (18:00-22:00). The Portable Sleep Monitor (PSM) was performed on the following 3 nights: the night before surgery (Sleep1), the first night after surgery (Sleep 2), and the third night after surgery (Sleep 3). Postoperative pain scores using visual analogue scoring scale, subjective sleep quality using the Athens Insomnia Scale, total dose of general anesthetics and PCA pump press numbers were also recorded.

Inclusion Criteria:

age between 30 and 55 years American Society of Anaesthesiologists physical status I or II.

Exclusion Criteria:

cardiovascular disease long term use of analgesia preoperative heart rate (HR) less than 50 beats/min second- or third-degree atrioventricular block sleep disorder sleep apnea syndrome history of abnormal operation or anesthesia recovery psychosis or a patient with a language communication disorder not willing to cooperate with the experimenter.

Patients who underwent elective laparoscopic abdominal surgeries under general anesthesia at Shengjing Hospital of China Medical University were enrolled in this study