General anesthesia is associated with loss of pulmonary functional residual capacity and consequent developement of atelectasis and closure of the small airway. Infants and young children are more susceptible to this lung collapse due to their small functional residual capacity.

Mechanical ventilation in a lung with reduced functional residual capacity and atelectasis increased the dynamic alveolar stress-strain inducing a local inflammatory response in atelectatic lungs areas know as ventilatory induced-lung injury (VILI). This phenomenon may appear even in healthy patients undergoing general anesthesia and predisposes children to hypoxemic episodes that can persist in the early postoperative period. During laparoscopy, pneumoperitoneum may aggravate the reduction of functional residual capacity as it generates a further increase in intra-abdominal pressure.

The increase in alveolar stress-strain cloud be reduced during pneumoperitoneum in theory, if normal functional residual capacity is restored and the transpulmonary pression is reached at the end of expiration of 0-1 cmH2O.

This is a prospective and observational study designed to measure transpulmonary pressure during pneumoperitoneum. The investigators will studied 20 mechanically ventilated pediatric patients schedule for abdominal laparoscopy surgery under general anesthesia.

Lung mechanics will be assessed during laparoscopy. Esophageal pressure will be measured by an esophageal ballon to measure transpulmonary pressure. Lung collapse will detected when transpulmonary pressure became negative and using lung ultrasound images. A lung recruitment maneuver will be applied if these patients present atelectasis during surgery. The optimal level of positive end-expiratory pressure (PEEP) if defined as the PEEP level when transpulmonary pressure remains positive during the PEEP titration trial of the recruitment maneuver.

Inclusion Criteria:

• Written Inform Consent by parents
• Programmed surgery
• Laparoscopic surgery
• Supine position
• American Society of Anesthesiologists classification: physical status I-II

Exclusion Criteria:

• Acute airway infection
• Cardiovascular or pulmonary disease

Pediatric patients aged 3 to 7 years old, schedule for abdominal laparoscopy surgery under general anesthesia with tracheal intubation