Inclusion Criteria:  Children between 1 and 5 years old, scheduled for elective adeno-tonsillectomy, tonsillectomy or adenoidectomy. Only patients whose parents are fluent in French or English will be enrolled  Exclusion Criteria:  Patients with neurological or cardiac congenital deficits, with cardiac arrythmias (non-sinus rhythm) Implanted pacemakers, with a history of prolonged resuscitation at birth, on chronic therapy with drugs that have known effects on sympathetic and parasympathetic activity (antimuscarinics, beta 2 adrenergic agonists Alpha 1-adrenergic antagonists or antiarrhythmic agents, Tricyclic antidepressants. ASA physical status III or higher and parent/guardian refusal. Patients be scheduled for surgery without an appointment at the Montreal Children's Hospital (MCH) Preoperative Clinic A surgery appointment within 24 hours of surgery, will not be enrolled into the study.  As this study will be conducted with only one NIPE monitor, and it will be devoted to the patient for about 1.5 hours, two consecutive patients cannot be enrolled in the study. In this case, the second patient will be considered eligible but excluded, and data will not be collected.