Inclusion Criteria:  Age ≤17 years; Scheduled for elective digestive tract surgery, orthopedic surgery, urological surgery or ear surgery under general anesthesia; ASA physical status I～Ⅲ; The informed consent form was signed by the patients or the guardians.  Exclusion Criteria:  The expected length of hospital stay of the patient is less than 48h; Patients expected to be admitted to the ICU after surgery; Patients expected to return to the ward with tracheal catheter after surgery; Be allergic to S (+) - ketamine; Patients with severe disorder of consciousness or mental system diseases (schizophrenia, mania, bipolar disorder, psychosis, etc.) or cognitive dysfunction; Patients with congenital heart disease or severely developmental retardation;  Patients with any of the following contraindications of S (+) - ketamine:  Patients with risk of serious rise of blood pressure or intracranial pressure; Patients with high intraocular pressure (glaucoma) or penetrating ocular trauma; Patients with poorly controlled or untreated hypertension (Resting systolic blood pressure greater than 180 mmHg, or resting diastolic blood pressure greater than 100mmHg); Patients with untreated or undertreated hyperthyroidism.