The morbidity of colorectal cancer and the surgery number among elderly is growing. The investigators need to provide more advanced and specific monitoring technology for these patients. Index of consciousness (IoC) monitor is now widely used among endoscopy, cholecystectomy and other common clinical applications. The investigators goal is to verify whether using IoC monitor could help to improve the postoperative recovery after colorectal surgery.

Participants will be randomly assigned, in a 1:1 ratio, to receive IoC monitoring or BIS monitoring during the operation as the criteria for adjustment of analgesics use. The randomization sequence will be computer-generated, and randomization will be performed in blocks and will be stratified according to participating center. The number of dialysis and patient's recovery after the transplantation will be recorded. The participation of each patient is scheduled till they discharge from hospital.

Inclusion Criteria:

• Patients aged over 60 years old that underwent Colorectal surgery in the First Affiliated Hospital of Xi'an Jiaotong University.

Exclusion Criteria:

• Having severe comorbidity history,for example,severe cardiac dysfunction
• Having central nervous system disease, severe endocrine, and history of mental disorders
• Alcoholic and long-term use of sedatives and opioids history
• Drug allergy history.