Total Intravenous Anesthesia in gastrointestinal surgery combined with dexmedetomidine given values of the propofol TCI and the economical effect of intravenous anesthetics

INTERVENTION: 1:Control group: (weight in kilograms * 1 / 8) normal saline intravenously in 15 minutes +10 mi / h normal saline until extubation ;2:Experimental group 1: intravenous infusion of 0.5ug/kg (weight) dexmedetomidine completed 15 minutes of scheduled +0.25 ug / kg / h constant intravenous infusion of dexmedetomidine given to extubation ;3:Group 2: intravenous infusion of 0.5ug/kg (weight) dexmedetomidine completed 15 minutes of scheduled +0.5 ug / kg / h constant intravenous infusion of dexmedetomidine given to extubation; CONDITION: Gastrointestinal disease PRIMARY OUTCOME: Extubation time;various total dose of propofol, fentanyl, remifentanil, dexmedetomidine intraoperatively;Value of propofol TCI;Recovery time; SECONDARY OUTCOME: Narcotrend value; INCLUSION CRITERIA: 1. Aged 18 to 64 years, gastrointestinal disease, undergoing elective gastrointestinal surgery patients; 2. General is still good, ASA grade 1 or 2 level; 3. Understood and signed informed consent clinical trials.