**1. Introduction**

The laryngeal mask is a well-established option for airway managemen<sup>t</sup> in pediatric patients undergoing general anesthesia for various surgeries [1]. This device can be used to secure ventilation in di fficult situations, for example, after primary failure of endotracheal intubation [2–4].

Laryngeal mask airway (LMA) provides a relatively safe airway for positive pressure ventilation (PPV) in children [5]. Pressure control ventilation (PCV) is widely discussed as the method of choice for delivery of PPV through an LMA. A study by Natalini et al. compared pressure-controlled ventilation and volume-controlled ventilation with the LMA. The study demonstrated that the use of PCV during general anesthesia with the LMA reduced the peak airway pressure compared with volume control ventilation at the same tidal volumes and inspiratory times [6]. Positive end-expiratory pressure (PEEP) is frequently used in tracheally intubated patients to increase oxygenation, but is rarely used with the LMA because the low pressure seal predisposes to oropharyngeal and esophageal air leaks [7].

The use of general anesthetic reduces functional residual capacity especially in children, resulting in increased intrapulmonary shunts [8]. PEEP reduces this shunt volume during controlled ventilation in patients with healthy lungs [9]. There are no guidelines for PEEP settings in pediatric patients. Nevertheless, anesthesiologists traditionally set PEEP to a lower level in pediatric patients than in adults, i.e., below 5 cmH2O [8].

Optimization of functional residual capacity is even more important in children since they have a lower capacity for elastic retraction and a lower relaxation volume, and as a result are more susceptible to atelectasis than adults [10]. However, there is little data on optimum ventilation using a laryngeal mask and applying PEEP.

The Supreme ™ laryngeal mask (S-LMA, a second-generation laryngeal mask) o ffers the option of simultaneous insertion of a gastric tube. This is important as, in contrast to airway managemen<sup>t</sup> using endotracheal intubation, use of a laryngeal mask is potentially associated with the risk of gastric air insu fflation with possible further consequences. But a randomized controlled trial by Drake-Brockman et al. evaluated the e ffect of endotracheal tubes versus LMAs on perioperative respiratory adverse events (PRAE) in infants [11]. The primary outcome of this study was the incidence of any PRAE in relation to the type of airway device used. The impact of LMA vs. endotracheal tubes (ETT) on the incidence of individual PRAE and their timing (intraoperatively and postoperatively) were assessed as secondary outcomes. This study showed a clear benefit of the use of an LMA compared with an endotracheal tube in a large number of infants undergoing minor elective surgery.

The aim of our observational investigation was to evaluate the e ffects on ventilation parameters during general anesthesia in children using pressure-controlled ventilation with the S-LMA at di fferent PEEP levels. Primary outcome parameters were changes of the dynamic compliance and end-tidal carbon dioxide (etCO2) to verify recruitment maneuver's with PEEP in lungs; secondary outcome parameters were the gastric air insu fflation during ventilation with three di fferent PEEP levels.
