Dreaming is a common, enduring, and fascinating part of the anesthetic experience, but its cause and timing remain elusive. Patients typically report that they were dreaming during anesthesia, but the actual timing of anesthetic dreaming is unknown. The following evidence supports the hypothesis that dreaming occurs intraoperatively and is related to light or inadequate anesthesia: (1) The incidence of dreaming has decreased as anesthetic techniques have improved; (2) dreamers exhibit more clinical signs of light anesthesia or report more awareness than non dreamers; (3) dreamers may receive lower doses of anesthetic drugs than non dreamers and emerge more rapidly from anesthesia; (4) the content of dreams may involve surgical topics or events occurring during anesthesia; and (5) in one study, the incidence of dreaming was lower in Bispectral Index (BIS)-monitored patients. Alternatively, dreaming may occur during emergence from anesthesia, when the brain is still affected by sedative concentrations of anesthetic drugs and the patient enters a sleep state. Few studies have assessed the relation between dreaming and depth of anesthesia, and their results were inconclusive.Most recently, in the B-Aware Trial, no differences in depth of anesthesia, as measured by BIS, were detected between dreamers and non dreamers. However, the patients were at high risk of awareness, and BIS data were collected manually and were only recorded in the BIS group and during maintenance. No studies investigating the relation between dreaming and depth of anesthesia during recovery were identified. Why is the investigation of dreaming during anesthesia important? Dreaming is one of the most common side effects of anesthesia but remains puzzling and requires explanation. Dreaming is sometimes distressing to patients and may decrease satisfaction with care. Some patients who report dreaming fear that their anesthetic was inadequate and that their experience was, in fact, awareness. Indeed, in a minority of cases, dreaming may truly represent near-miss awareness. The investigators therefore tested the hypothesis that dreaming during anesthesia is associated with light or inadequate anesthesia, as evidenced by higher median BIS values during maintenance of anesthesia. The investigators also explored the depth of anesthesia until emergence, the form and content of dreams, the predictors of dreaming during anesthesia, and the effect of dreaming on quality of recovery and satisfaction with anesthetic care

Inclusion Criteria:

• between 18 and 70 years
• with an ASA physical status of I or II

Exclusion Criteria:

• presence of sleep disorders
• pain syndrome
• cardiovascular disease
• sleep apnea syndrome
• psychosis
• history of opioid usage
• history of abnormal operation or anesthesia recovery
• unwillingness to provide informed consent
• a patient with a language communication disorder