The incidence of atelectasis is high in patients undergoing general anesthesia. This may cause oxygenation impairment and further contribute to post-operative pulmonary complications. As important airway management devices for general anesthesia, few studies have compared the impact of laryngeal mask airway and spontaneous breathing on atelectasis. Through the study, the distribution of the pulmonary ventilation of children undergoing an elective and standard procedure in our center (H.U.D.E.R.F.) will be studied using electric impedance tomography.

Children from 1 year-old to 6-year-old, ASA physical status I or II who will undergo elective circumcisions under general anesthesia associated with regional anesthesia (Penile Block10) at the One Day Clinic of H.U.D.E.R.F. (Hôpital des Enfants Reine Fabiola - Brussels - Belgium).

Patients will be allocated to three different group in a ration of 1:1:1.

• Group 1: spontaneous mask ventilation (20 patients).
• Group 2: spontaneous laryngeal mask (LMA) ventilation (20 patients).
• Group 3: spontaneous-pressure support LMA ventilation (LMA SV-PS) (20 patients).
• Standard monitoring for the inductions of the anesthesia will include non-invasive blood pressure (NIBP), pulse oximetry (SpO2), Electrocardiogram (ECG), End-Tidal CO2 (EtCO2), End Tidal Sevoflurane concentration (EtSev %), inspired fraction of oxygen (FiO2), body temperature (rectal thermometer).

Induction is based as well on the local routine protocols using an inhalation induction of the patient with Sevoflurane (Fet of 6-8%) and a recommended FiO2 from 80-90% maximum until the stabilization of the induction. Then the FiO2 will be decreased at least under 40% and Sevoflurane adapted to the need of the deepness of the anesthesia (both at the discretion of the anesthesiologist in charge of the patient).

Depending on the randomization, the patient will undergo the surgery either with spontaneous face mask ventilation (group 1), LMA spontaneous ventilation (group 2), or LMA SV-PS (group 3) (during which the pressure support will be adapted at the discretion of the anesthesiologist but with a tidal volume included in the range of 6-10ml/kg).

Electrical impedance tomography measurements:

The effects of the spontaneous breathing (mask ventilation or LMA) or the pressure support ventilation (LMA SV-PS) on atelectasis formations and the distribution of the ventilation will be assessed using electrical impedance tomography.

The device used during the study will be the "PulmoVista 500"; it will be provided by Dräger (Lübeck, Germany) free of charge and without any obligation or results/conclusions requested by Dräger. The device is approved CE (European regulation) and will be used in the conditions for which it has been designed.

A reusable belt with 16 evenly spaced electrodes will be placed around the chest of each patient included in the study between the 4th and 6th ribs as recommended by Dräger.

The EIT measurements will be taken of 4 different moments:

T1: Before induction of the anesthesia in the preoperatory waiting room (and at least 30 min after the premedication).

T2: After the induction of anesthesia (GA and penile block), just before the beginning of the surgical procedure.

T3: After the end of the surgical procedure, just before discontinuing the general anesthesia.

T4: Before the discharge of the PACU.

Inclusion Criteria:

• Children undergoing elective circumcision
• Age 1 to 6 years
• ASA class I or II

Exclusion Criteria:

• Any history of lung diseases, congenital heart diseases or abdominal diseases that could interfere with lungs dynamic.
• ASA physical status11 > II.
• Patients whose weight is less than 10 kg.
• The use of Jackson-Rees device12.
• Contraindication for premedication.
• Contraindication for mask ventilation or laryngeal mask ventilation13.
• Contraindication for regional anesthesia.
• Need for opioids administration during surgery.
• Patients with uncontrollable movements of the body.
• Inability of parents/tutors to understand French or Dutch.
• Patients whose parents do not agree with their participation in the study
• Patients with thoracic perimeters (between 4th and 6th ribs) less than 37.5 cm (minimal size for the pediatric EIT belt) or more than 72 cm (maximal size for the pediatric EIT belt)
• Patients with damaged skin or impaired skin contact of the electrodes due to wound dressings.
• Patients with spinal lesions or fractures (acute or recent)
• Patients with pacemaker, defibrillators, or other electrically active implants