Pupillometry-guided Remifentanil Infusion Versus Conventional Administration in Children

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