This prospective observational cohort study will assess whether perioperative short-term heart rate variability (HRV) indices and early inflammatory cytokine levels are associated with respiratory and cardiac adverse events in children undergoing elective adenoidectomy, tonsillectomy, or adenotonsillectomy under general anesthesia. HRV will be recorded noninvasively from 30 minutes before surgery until discharge from the post-anesthesia care unit. Serum cytokines will be measured from 3 mL of residual blood obtained after induction of anesthesia. The study aims to identify perioperative physiologic markers associated with a lower or higher risk of adverse events, thereby supporting safer anesthetic planning.