High inspired oxygen concentrations (FiO2 0.8) during and after operative procedures have been recently recommended [1,2]. The clue is that these higher fractions might reduce the incidence of surgical site infections [3]. However, high FiO2 strategies have many drawbacks. First, it may generate reactive oxygen species leading to oxidative stress and DNA damage [4]. Second, the use of high FiO2 during induction and recovery is the most common cause of resorption atelectasis [5]. The rapid absorption of oxygen and loss of the splinting effect of nitrogen is the cause of such a phenomenon [4,5].

Intraoperative lung collapse and atelectasis reduce lung compliance and worsen oxygenation indices in the perioperative period increasing the incidence of postoperative pulmonary complications (PPCS) with higher morbidity and mortality [6,7]. Judicious use of FiO2 concentrations during induction and recovery of anesthesia (FiO2 0.8) with low concentrations during maintenance (FiO2 0.35) have been investigated in many research studies [[8], [9], [10]].

Pediatric physicians are still reluctant to accomplish low FiO2 strategies in children with a large debate on this concept. Children are more prone to the development of atelectasis because of their more compliant chest wall necessitating a low FiO2 strategy [5]. Meanwhile, they are more prone to hypoxemia and desaturation because of their smaller functional residual capacity, higher metabolic rates, and increased incidence of difficult airway management necessitating a high FiO2 strategy to increase the margin of safety in this vulnerable population [11]. The consequences of using high FiO2 in children are not fully investigated.

Ultrasonography is a radiation-free, bedside noninvasive tool that has recently enabled physicians to diagnose intraoperative atelectasis and to guide the alveolar recruitment maneuvers commonly performed to open lung alveoli with high sensitivity and specificity [12,13].

This study aimed to evaluate the effect of high FiO2 on the development of intraoperative atelectasis in mechanically ventilated children using lung ultrasound (LUS) and to investigate the association between the LUS aeration score and the patient's clinical variables and oxygenation indices. The primary endpoint was the correlation between the LUS score and the arterial oxygenation (PaO2/FiO2 ratio). The secondary endpoints were the pulmonary mechanics, arterial blood gas analysis, and perioperative respiratory complications.