Randomization will be done by computer generated numbers and concealed by serially numbered,opague and sealed envelopes. The details of the series will be unknown to the investigators and the group assignment will be kept in asset of sealed envelopes each bearing only the case number on the outside. Prior to surgery the appropriate numbered envelopes will be opened by the nurse, the card inside will determine the patient group. All children will be premedicated with oral midazolam 0.5mg/kg half hour before procedure and atropine at a dose of 0.01-0.02 mg/kg (IM). Continuous electrocardiogram (ECG), pulse oximetry, non-invasive arterial blood pressure, and temperature monitoring will be applied and all patients will be induced with inhalational anesthetic using Sevoflurane+ oxygen (O2) with mac 6%. After deepening of the anesthesia, intravenous (I.V.) line will be inserted and fentanyl 1μg/kg. Patient will be divided into two groups; group S (spontaneous) will be intubated and maintained spontaneously with Ayres T piece circuit on isoflurane + oxygen with mac 2% and with fresh gas flow 2 times minute ventilation of patient to avoid co2 rebreathing . Group C (controlled) will receive muscle given in the form of atracurium 0.5mg/kg and patients will be intubated by appropriate size of endotracheal tube. Patients in controlled group will be ventilated at 6 ml/ kg tidal volume, Inspiratory to expiratory (I: E) ratio 1:2, Fio2 1 and PEEP 5 cmH2o.