Compare the effects of sevoflurane or propofol on perioperative glucose metabolism in patients undergoing laparoscopic colorectal cancer surgery

Interventions: Group S:induction 2-3% and maintenance 1.5-2.5% of sevoflurane during operation;Group S+L:induction 2-3% and 1.5-2.5%maintenance of sevoflurane during operation, lipid emulsions 1mg/kg/h during operations;Group P:induction and maintenance of propofol 3.0-4.0ug/ml during operation Primary outcome(s): asprosin;blood glucose;insulin Study Design: Parallel