General anesthesia is a medically induced state of low reactivity consciousness involving amnesia, immobility, unconsciousness, and analgesia, which is similar to natural sleep. Its aim is to create a state of sensory deprivation to induce a lack of motor reaction to stimuli and to obtain an explicit amnesia. 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.Several studies also indicated that circadian rhythms existed in human and controlled by a main internal central clock, the suprachiasmatic nuclei, located in the anterior hypothalamus, which produce and regulate biological rhythms such as sleep arousal, hormones and metabolism could also affect the dose of general anesthesics, which lead to different postoperative recoveries and may have different effects on postoperative sleep quality. Previous studies proved that postoperative sleep disturbances and poor sleep quality are associated with higher postoperative pain, changes in behavior and poor emotional well-being, which could further aggravate postoperative sleep quality. At present, there are few studies which are about the effect of circadian rhythm for different timing of surgery on intraoperative anesthestic requirement, postoperative sleep quality and pain under general anesthesia.

eighty-four patients scheduled for elective laparoscopic abdominal surgeries under general anesthesia were randomly assigned to receive operation in the Day Group (8:00-12:00) and the Night 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 postoperative adverse effect were also recorded

Inclusion Criteria:

• age between 18 and 65 years
• American Society of Anaesthesiologists (ASA) physical status I or II.

Exclusion Criteria:

• cardiovascular disease
• long term use of analgesic
• 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 did not provide informed consent