The investigators hypothesized that intraoperative opioid consumption would be different between remimazolam and propofol if the ANI-guided remifentanil continuous infusion rate was adjusted when the depth of anesthesia was maintained at similar depths with remimazolam or propofol under total intravenous anesthesia. The purpose of this study is to compare the intraoperative remifentanil requirement in patients undergoing total knee arthroplasty when the intraoperative remifentanil dose adjustment was performed under the ANI guidance while maintaining a similar depth of anesthesia with remimazolam or propofol.

Inclusion Criteria:

1. Patients 19~80 years of age who are expected to elective total knee arthroplasty under general anesthesia
2. ASA PS 1-3

Exclusion Criteria:

1. Second total knee arthroplasty under a prior plan of staged total knee arthroplasty, both
2. Previous hepatectomy or liver transplant
3. Estimated glomerular filtration rate < 30 mL/min/1.73m2
4. Patients with moderate or more hepatic impairment (AST/ALT is more than 2.5 times the upper limit of normal)
5. Uncontrolled hypertension (systolic blood pressure > 160mmHg)
6. Acute narrow angle glaucoma
7. Myasthesia gravis
8. Known allergy to the drugs included in the study
9. Cardiac arrhthmia (non-sinus rhythm)
10. Taking drugs that affect the autonomic nervous system of diabetes
11. Psychiatric or neurologic disease (major depression disorder, dementia or cerebral infarction)
12. History of drug or alcohol abuse