The purpose of this study is

1. to evaluate effect of high FiO2 on the development of intraoperative atelectasis in mechanically ventilated children using LUS.
2. to investigate the correlation between lung consolidation score and patient clinical variables including pulmonary mechanics, Sao2%, ABG, and perioperative respiratory complications.

The WHO and United States centers for disease control and prevention (CDC) recently recommended the administration of 80% inspired oxygen fraction (Fio2) during and immediately after surgery performed with general anesthesia and endotracheal intubation.

The recommendation was based on some data suggesting that intra-operative high Fio2 reduces incidence of surgical site infections.

The dilemma of applying high or low perioperative FiO2 arises in daily practice of pediatric anesthesia because children are at increased risk of developing hypoxemia due to their physiological characteristics including smaller functional residual capacity and increased metabolic requirement compared with adult.

However, considering that atelectasis occurs in most pediatric patients undergoing general anesthesia, it is important to titrate perioperative level of FiO2 to minimize the risk of developing atelectasis and hypoxemia.

The use of FiO2 80% at induction and emergence, whilst limiting FiO2 to 35% during maintenance of anesthesia, may prevent the occurrence of atelectasis and ensure sufficient oxygenation.

Conversely, the use of FiO2 100% at induction and emergence, which is reduced to FiO2 80% during maintenance of anesthesia, may increase the margin of safety to avoid hypoxemia.

In children, the pulmonary consequences of using high FiO2 during general anesthesia have not been fully characterized over the early perioperative period. LUS has shown reliable sensitivity and specificity for diagnosis of anesthesia-induced atelectasis in children [7]. It can identify children needing a recruitment maneuver to re expand their lung and help optimize ventilator treatment during anesthesia.

Our hypothesis is that clinical data are necessary to validate the lung sonographic findings of atelectasis and negative consequences of administrating high perioperative oxygen concentration.

Inclusion criteria:

• Age of 1-6 years.
• ASA physical status (I-II).
• Endotracheal intubation and mechanical ventilation.
• Elective non-abdominal and non-thoracic surgery
• lasting for more than 2 hours.

Exclusion criteria:

• ASA classification more than II
• Thoracic or abdominal surgery.
• pre-existing lung disease.
• Pre-operative chest infection or abdominal chest US finding. Any thoracic deformity Patients with cardiac, liver or kidney disease.

Age of 1-6 years.

• ASA physical status (I-II).
• Endotracheal intubation and mechanical ventilation.
• Elective non-abdominal and non-thoracic surgery
• lasting for more than 2 hours.