Comparative Clinical Study of Efficacy and Safety of Remimazolam and Propofol in Patients Undergoing Elective Surgery Under General Anaesthesia

Inclusion Criteria: 1. Signed informed consent form to participate in the study prior to initiation of any study-related procedures, and possibility to follow the protocol. 2. Body mass index (BMI) calculated as body weight (kg)/height (m)2, ≤ 30 kg/m2. 3. Patients hospitalized for elective surgery in whom intraoperative mechanical ventilation using tracheal intubation (oropharyngeal or nasotracheal) is planned. 4. Patients for whom the duration of inpatient hospital stay for at least 2 days (1 day before and 1 day after the surgery). 5. American Society of Anesthesiologists scale (ASA) I - II functional class. 6. For females: negative result of a pregnancy test (urine test using test strips) since the moment of enrollment to the study prior to administration of the test drug/reference drug, as well as consent to use birth control methods throughout the entire study (since the moment of enrollment to the study until the complete ending of the observation period) for women of childbearing potential. Female patients who did not have menstrual periods for 2 years or more before enrollment to the study or female patients who underwent a surgical procedure (surgical sterilization, bilateral oophorectomy, hysterectomy etc.) are considered females of no childbearing potential. 7. For males: consent to use birth control methods throughout the entire study (since the moment of enrollment to the study until the complete ending of the observation period). Exclusion Criteria: 1. Patients in whom local anesthesia is planned (subarachnoid (spinal) block, epidural anesthesia or peripheral nerve block) during the period from admission into an operating room till extubation on Day 1 (administration of the test drug/reference drug). 2. Patients in whom organ transplantation is planned. 3. Patients in whom heart surgery is planned. 4. Patients with uncontrolled hypertension (e.g. systolic blood pressure ≥160 mm Hg while on antihypertensive therapy). 5. Patients in whom total bilirubin level ≥ 51 mmol/l or aspartate aminotransferase (AST) or alanin aminotransferase (ALT) level ≥ 2.5 upper limit of normal (ULN) (or ≥100 U/L) during the period from Day -14 till their admission to the operating room. 6. Patients in whom serum creatinine level ≥140 mmol/l during the period from Day -14 till their admission to the operating room. 7. Patients undergoing an urgent surgical procedure. 8. Patients in whom a surgical procedure lasting less than 1 hour is planned. 9. Patients in whom extubation problems are anticipated due to the expected necessity of prolonged respiratory support using tracheal intubation. 10. Patients with history of resistance to benzodiazepines or propofol. 11. Patients with history of hypersensitivity to benzodiazepines, propofol, opioid analgesics, fentanyl citrate, rocuronium bromide, sugammadex sodium, flumazenil, naloxone, or other anesthetics or benzodiazepine receptor antagonists. 12. Acute open-angle glaucoma. 13. Myasthenia gravis or myasthenic syndrome. 14. Patients with shock or coma. 15. Acute alcohol intoxication. 16. Patients with epilepsy. 17. Patients with inserted pacemaker with a bioelectric impedance sensor. 18. Patients in whom correct evaluation of the bispectral index (BIS) cannot be performed due to a structural brain disorder. 19. Patients who received benzodiazepines, in case the period between their discontinuation and the administration of the test drug/reference drug is less than 5 half-lives of benzodiazepine (or 5 half-lives of the active metabolites, if applicable), or in case benzodiazepines are revealed in urine test during the screening. 20. Patients taking psychotropic drugs (depot forms should be discontinued at least 1 month prior to the screening; administration of typical forms should be discontinued at least 1 week prior to the screening). 21. Patients in whom massive blood loss is expected (e.g. at least 15% of the circulating volume) during the surgery. 22. History of severe allergic reactions. 23. Alcohol and/or drug abuse or history of such abuse. 24. Nursing women. 25. Patients in whom any other unregistered drugs (including prescription of unregistered combination products or new pharmaceutical forms during the clinical study) are planned within 120 days prior to administration of the study drugs. 26. Patients admitted incapacitated to give an informed consent due to dementia, etc. 27. Patients receiving (had a history of receiving) any medicinal product containing the active substance similar to remimazolam. 28. Patients with exacerbation of existing mental disorders. 29. Patients with a confirmed or suspected malignancy of any localization. 30. Detection of viral hepatitis B and C, HIV infection or syphilis based on the results of screening investigations. 31. Patients considered not conforming to the objectives of this study for any other reasons by the Principal Investigator or the Investigator.