Medical literature about awareness during general anesthesia is rare in China, and some small sampled studies in China showed a significantly higher incidence (1.5～6%) of intra-operative awareness compared with western countries. The investigators sponsored this multicenter, large sampled, prospective study to determine the incidence of intra-operative awareness in China, and the preservation effect of BIS monitor on the incidence of awareness.

Background: The incidence of awareness in patients undergoing general anesthesia has been reported in as many as 0.1～0.2% in western countries. But so far，medical literature about awareness during general anesthesia is still rare in China, and some small sampled studies in China showed a significantly higher incidence (1.5～6%) of intra-operative awareness. We believed that this multicenter, large sampled, prospective study would be very necessary for us to determine the incidence of intra-operative awareness in China, and analysis of the relevant factors would help us to understand why was the incidence of awareness in China much higher than that in western countries.

Methods: This is a prospective, nonrandomized descriptive cohort study that was conducted at 25 academic medical centers in China. 11,197 patients (age>12, intubation or LMA during anesthesia) form 25 medical centers were enrolled to be interviewed by research stuff for evaluation of awareness at the 1st and 4th day after their general anesthesia. The structured interview questions were:⑴What is the last thing you remembered before you went to sleep? ⑵What is the first thing you remembered when you woke up? ⑶Can you remember anything between these two periods? ⑷Did you dream during your operation? ⑸What was the worst thing about your operation? An evaluation committee independent from the research stuff was constituted to verify the data from the medical centers. And then the incidence of intra-operative awareness in China was determined. General condition and details of the anesthesia procedure of the patients were also recorded during the anesthesia for a binary logistic regression analysis.

Inclusion Criteria:

• Patients received general anesthesia with tracheal intubation or LMA
• Apparently normal mental status

Exclusion Criteria:

• Pediatric patients (<12 yr)
• Those who could not be interviewed in 24 hours after the operations
• Those unable to communicate in common spoken Chinese

The subjects would be selected from the patients of the 24 hospitals who would undergo general anesthesia during different kinds of operations in different areas around China after the written informed consents obtained. Each hospital would continuously provide 500～600 subjects for the investigation.