This prospective randomized controlled study will compare the effects of sevoflurane and desflurane on the Analgesia Nociception Index (ANI) in adult patients undergoing general anesthesia. Participants will be randomized to maintenance anesthesia with either sevoflurane or desflurane, and ANI responses to a standardized nociceptive stimulus will be measured under equi-minimum alveolar concentration (age-adjusted 1.0 MAC) conditions. The primary objective is to compare the change in ANI before and after tetanic stimulation between the two anesthetic groups. Secondary measurements will include bispectral index, blood pressure, heart rate, and end-tidal anesthetic concentration around the time of stimulation.

This prospective randomized controlled study will compare the effects of sevoflurane and desflurane on the Analgesia Nociception Index (ANI) in adult patients undergoing general anesthesia. Conventional indicators of intraoperative nociception, such as changes in blood pressure, heart rate, and patient movement, can be influenced by anesthetic depth, vasoactive agents, and intravascular volume status. ANI is a heart rate variability-based monitoring index developed to provide a more objective assessment of nociception during general anesthesia. Previous studies have suggested that sevoflurane and desflurane may produce different nociceptive responses at equi-minimum alveolar concentration (MAC), but comparative data using ANI are lacking. In this study, eligible patients will be randomized to maintenance anesthesia with either sevoflurane or desflurane. After standardized induction and stabilization at age-adjusted 1.0 MAC, a standardized tetanic stimulation will be applied, and ANI will be recorded 1 minute before and 1 minute after stimulation. The primary objective is to compare the between-group difference in ANI change in response to the same nociceptive stimulus under equi-MAC conditions. Secondary assessments will include bispectral index, blood pressure, and heart rate measured around the time of stimulation.

Inclusion Criteria:

• Adults aged 19 to 79 years
• Patients undergoing general anesthesia
• American Society of Anesthesiologists (ASA) physical status I or II

Exclusion Criteria:

• History of taking medications that may affect the central nervous system or autonomic nervous system (e.g., anticholinergics, beta-blockers, antidepressants, anxiolytics, hypnotics, or analgesics)
• Known hypersensitivity to sevoflurane, desflurane, or other halogenated anesthetics, or a personal or family history of malignant hyperthermia
• Neurologic or psychiatric disorders (e.g., depression, dementia, or cerebral infarction)
• Arrhythmia
• Diabetes mellitus
• Drug abuse or alcohol abuse
• Vulnerable subjects
• Patients aged 80 years or older
• Patients with impaired consciousness or those judged to lack the capacity to provide informed consent