1. Context
Supraglottic Airway Devices (SADs) are widely used for airway management (1). Children who undergo surgeries benefit most from the use of SADs. A variety of SGAs are used for the management of a difficult airway as well as a conduit for tracheal intubation in children (2). Advantages of endotracheal intubation assisted by SADs such as effortless insertion, improved alignment of the glottic opening, and continuous patient oxygenation and ventilation, have been well documented. In addition, hemodynamic stress response to intubation by SADs is less than the conventional methods (3). Such devices could be an excellent alternative for patients with previous history of difficult intubation, limited neck movement, and unstable cervical spine (4). Moreover, SADs facilitate overcoming upper airway obstruction and provide a hands-free airway support with a relatively straightforward path to the larynx (5). However, despite all evidence, choosing the optimal SAD is not a simple decision.

2. Objective
 The present review study aimed to examine the literature regarding pediatric SADs, to draw recommendations for future investigations and integrate the evidence.

3. Data Sources
The following steps were taken to thoroughly review the relevant literature. We conducted an electronic search was conducted on MEDLINE, Embase, CINAHL and PubMed databases. We also searched the Cochrane database (CENTRAL), and Web of Science up to July 1, 2017.

4. Study Selection
 Studies on subgroups like those comparing devices in children and reports of their usage were included. The keywords used for the search strategy were “supraglottic device”, “supraglottic airway device”, “laryngeal mask”, “children”, “child,” and “pediatric”. A review of reference lists of articles was performed to identify further references. Two authors independently scanned the titles and abstracts identified by the above-mentioned search strategies. All randomized trials comparing any types of supraglottic airway devices in children were included. Similarly, cost-effectiveness analysis and case reports of rare complications in the emergency ward were also included in this review to consider every chance of adverse effects for clinicians.

5. Data Extraction
 Of 112 potential studies, 53 full texts of papers were accessible. Initially, the full text versions of potentially eligible studies selected by at least one reviewer were assessed. Any disagreement was resolved through discussion. Papers in English were considered eligible. Then, the extracted data were sorted into prepared data extraction tables. We extracted such data as patients’ frequency, type of Laryngeal Mask Airway (LMA), study design and predominant findings. Finally, a structured narrative summary of the studies was conducted using 30 papers related to the supraglottic devices for children.

6. Results
A comprehensive search was conducted. The following SADs were included in the review: LMA Classic, LMA ProSealTM, LMA Supreme, LMA FlexibleTM, LMA Unique, i-gel, Laryngeal TubeTM, self-pressurized air-QTM, Cobra perilaryngeal airwayTM, and Ambu Aura-iTM. In total, 30 papers related to supraglottic devices for children were identified. These qualitative studies were conducted in various settings, including accident and emergency department or operating rooms. A review of recent literature is presented in Table 1 and further discussed in the article.
A brief review of the recent literature indicate that SADs such as the i-gel, LMA ProSeal and Cobra perilaryngeal airway demonstrate higher OLP in most studies focusing on OLP. Evidence also revealed that the risk of device failure may be lower with LMA ProSeal, LMA-Classic and LMA-Unique (34-36), but higher with i-gel (37, 38). Moreover, the risk of blood staining of the device was greatly lower with i-gel compared to LMA-Classic and LMA ProSeal. In summary, the LMA ProSeal seems to be the best supraglottic airway device for children because of its high OLP and low risk of insertion failure. Also, i-gel appears to be a very functional tool. 

6.1. Outcome measures for rating success in LMA insertion
6.1.1. Cuff pressure
When the supraglottic cuff pressure is more than the mucosal perfusion pressure, postoperative pharyngolaryngeal symptoms such as a sore throat (dysphagia or dysphonia) or local mucosal trauma and nerve injuries are expected (39). SGAs with inflatable cuffs are prone to over inflation and may cause pressures higher than 60 cm H2O (40). Elevated pressures do not provide better seal, and are conversely liable to cause more morbidity (41, 42).

6.1.2. Oropharyngeal Seal Pressure (OSP)
An effective glottic seal is necessary for efficient ventilation. Moreover, an appropriate seal facilitates the maintenance of preferred anaesthetic depth without polluting the environment with the leaked gases. It also decreases leak into the esophagus, preventing rise in intragastric pressure and the risk of regurgitation (43). 

6.1.3. Fiberoptic view through a supraglottic device
Most studies have correlated the Fiberoptic BronchosCopy (FOB) view through the SGA with the ease of intubation and ventilation (36). However, the FOB scoring is challenged, as a dependable tool for SGA positioning (17) (Figure 1). The usage of fiberoptic score was suggested by Cook and Cranshaw (44). Left to right view: View I (I = ideal), View H (H: too high), and View L (L: too low), respectively; Arrow: lingual tonsils. Further evidence about FOB in different studies are demonstrated in Table 1 A full glottic view (although it seems unnecessary) is recommended for primary ventilation, to avoid possible trauma.

6.1.4. Problems and failures
Airway obstruction can arise due to malposition, obstruction by the epiglottis, laryngospasm, biting, or kinking of the tube. Light plane of anesthesia can also lead to laryngospasm and airway obstruction in children (37). Lingual edema and aspiration of stomach contents are other potential complications. The younger and smaller the child, the higher the risk of developing problems in this area (25, 30). Higher experience significantly decreases such problems (18).

7. Discussion
The main findings of the current study were as follows: i-gel, LMA ProSeal, and Cobra perilaryngeal airway had a higher OLP than the other devices; the risk of device failure may be lower with LMA-ProSeal, LMA-Classic, and LMA-Unique (34, 35), but higher with i-gel (37, 38). On the other hand, most studies demonstrated that the risk of blood staining device was considerably lower with using i-gel, compared to the LMA-Classic and LMA-ProSeal (40). However, high quality randomized trials are required to confirm the results regarding laryngeal tube. 

 

 

 

 

A variety of modern SGAs for using in children have emerged. It is important to introduce those into practice and assess the potential advantages and disadvantages of each device through clinical evaluations. Table 1 summarizes the discussed SGAs and outlined potential areas of concern. Despite the variety of modern devices, the cLMA, ProSeal, and Unique are still the best devices in pediatric use for different conditions. The cLMA has been the standard SGA for many years. However, many other first generation devices have been available in small sizes with further features and better performance, since 2003 (18, 30, 45). For example, Cobra PLA was designed to be placed in the hypopharynx and composed of a breathing tube with a wide distal end and a number of slots or bars (46). 
A cuff is attached proximal to the wide part, and serves to seal off the distal end from the upper airway when it is inflated and a softened ‘tongue’, which bends for better passage (16). Variations of LMAs like ProSeal, Unique, Supreme, and iLMA have been marketed in practice and discussed in the literature (47). The i-gel is rather an exceptional SAD with a gel-like thermoplastic and a non-inflatable cuff (48) which achieves an effective perilaryngeal 

 

 

seal because of its feasibility to shape patient’s airway structure (20). In addition, the device is equipped with a bite block and a buccal cavity stabilizer that stop the device malrotation and a gastric channel (22). 
The recent studies demonstrated the efficacy and safety of the device, for example, Pejovic in a manikin study, compared i-gel with face mask and reported that the i-gel accomplished a 100% success rate on all occasions by trainees (10). Yeoh, et al. also reported the advantages of size 2 i‑gel™ in children in terms of ease of insertion and low number of attempts on insertion (19). Novel design of i-gel made it a suitable tool with an appropriate OLP and low risk of complication.
LMA Supreme is similar to LMA ProSeal except its single usage and its introducer shaft features. Various studies have declared acceptable airway characteristics of LMA supreme to apply in children (20, 22, 35, 36). Jagannathan et al. (49) and Francksen et al. found it comparable with the LMA ProSeal and i-gel, respectively and recommended it as a useful alternative to ProSeal LMA (50). A prospective cohort study by Gaitini et al. compared the Supreme size II with LMA ProSeal and found it similarly effective on higher oropharyngeal seal pressure during spontaneous ventilation in children (51) that make it an optimal tool in difficult or emergency airway management.
The air-Q™ LMA is also a modern SAD that allows passage of cuffed tracheal tubes and has the option of successive removal. In addition, the airway tube is broader, more rigid, and curved. Air-Q features facilitate the use of ILA as a conduit for tracheal intubation (23). Finally, the Ambu Aura-i is easy to insert and provides equal or better OSP than CLMA and Unique, respectively, in adults (52, 53). It is also a suitable tool for blind endotracheal intubation (44). Therefore, it has become a frequently used device for various short surgical procedures, even in children. These devices are definitely appropriate to apply on children undergoing many surgical procedures. Further research is required to investigate the most appropriate supraglottic airway devices in diverse clinical situations and various conditions among children.

8. Conclusions
The LMA ProSeal and i-gel may be the best optimal supraglottic airway devices for children due to their unique features. However, there is little knowledge in this regard and more research studies must be conducted to recognize the most appropriate supraglottic airway devices in diverse clinical situations and various conditions in children.

Ethical Considerations
Compliance with ethical guidelines
There is no ethical principle to be considered doing this research.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors contributions
The authors contributions is as follows: Investigation, writing review and edit: Mir Ahmad Hendinezhad, Anahita Babaei; and Supervision: Afshin Gholipour Baradari.

Conflict of interest
The authors declare no conflict of interest.


References