Our study aims to compare the total intravenous dose of remifentanil per anesthesia hour and body weight in two groups of pediatric surgical patients - an interventional group with remifentanil infusion under pupillometry monitoring, and control group without pupillometry - to figure out whether pupillometry monitoring may reduce remifentanil consumption during anesthesia while providing sufficient analgesia for surgical noxious stimuli.

comparison of total used opioid

Inclusion Criteria:

• Pediatric patients who are at 3 to 6 years of age, scheduled to undergo elective surgery with estimated time of operation 2 hours or longer, under general anesthesia
• American Society of Anesthesiologists physical status classification (ASA class) I - II
• Patient and his/her parents are willing to participate after explanation of the purpose, materials, methods, possible risks and benefits of the research

Exclusion Criteria:

• History of hypersensitivity/allergic reaction to the drugs which are used in general anesthesia
• Preoperative use of analgesics, antipsychotics and/or antiepileptics
• Mental retardation
• Medications related to hindrance of autonomic nerve system activity, e. g., beta blockers
• Underlying ophthalmic diseases

Participant does not know in which of the groups he/she is allocated. Only a care provider (an attending anesthesiologist who is responsible for the patient's anesthesia) knows the group which the patient belongs to.

Investigator and outcomes assessor does not know in which of the groups the patient is allocated, since the group name will be just recorded as "A" or "B" until data analysis of the last participant is done.