The investigators invented the baby enclosed afferent reservoir anesthesia circuit (Baby EAR) which could be used safely in children between 5 and 20 kg, using a fresh gas flow of 2.5 and 3 L/min in the spontaneous breathing and controlled breathing, respectively. There has as yet been no study comparing the minimal fresh gas flow between the Baby EAR and Jackson-Rees anesthesia circuit (JR).

After intubation, a caudal block with 0.25% bupivacaine with adrenaline :200,000 0.5 to 1 mL/kg was done. Anesthesia was maintained with a 50% N2O/O2 combination with sevoflurane 1 to 3%, adjusted to ensure a proper anesthetic level to achieve normal vital signs and to keep the end-tidal CO2 (ETCO2) <60 mmHg. Fentanyl 1 μg/kg/h was infused during the procedure. All patients were pontaneously ventilated with FGF 500 mL/kg/min at the start of each anesthesia breathing circuit, waiting for the depth of anesthesia to be maintained and the patient to spontaneously breathe for at least 10 minutes. Baseline ETCO2 and imCO2 were then measured. The pulse rate, blood pressure and respiratory rate were recorded every five minutes.

The FGF was reduced by 50 mL/kg/min every five minutes, waiting for the imCO2 to be regularly maintained at least 60 sec. The ETCO2 and imCO2 values were recorded until rebreathing occurred (imCO2 >2 mmHg) and measurements continued until rebreathing was not clinically acceptable (imCO2 >6 mmHg). The minimal FGF before rebreathing occurred (FGF of imCO2 ≤2 mmHg) is the amount of gas that does not cause rebreathing. The minimal FGF for which rebreathing was still acceptable (FGF of imCO2 ≤6 mmHg) is the amount of gas that was clinically acceptable. After switching the anesthesia breathing circuit, the FGF was increased to 500 mL/kg/min for 10 minutes and the procedure was repeated. The minimal FGF before the rebreathing occurred and the FGF at hich rebreathing was still clinically acceptable were recorded. After extubation, all of the patients were observed in the PACU and relevant factors recorded until there was good recovery from anesthesia before sending the patient back to the ward.

Inclusion Criteria:

• weight between 5 and 20 kg
• ASA physical status I or II
• scheduled for general anesthesia

Exclusion Criteria:

• has respiratory or cardiovascular disease
• can not breathe spontaneously during anesthesia
• for whom the caudal block can not be done