Laryngeal Mask Airway Supreme in Children: A Retrospective Audit

The laryngeal mask airway (LMA) Supreme (LMAS) is a sophisticated, second-generation supraglottic airway device, with an improved seal, and gastric access. It is a capable device for use in more complex procedures and in younger children. No study has been able to analyze a large pediatric sample of patients to assess how the LMAS is being utilized. In this retrospective audit

T he laryngeal mask airway (LMA) Supreme (LMAS) (Teleflex ® Inc., Morrisville, NC, USA; Figure ) is a sophisticated, secondgeneration supraglottic airway device designed for single use, with an improved seal, gastric access, and easy insertion (1).It combines the features of the LMA Fastrach, LMA ProSeal, and LMA Unique.Like the LMA ProSeal, the LMAS has two lumens: an airway tube and a drain tube (DT).A correctly positioned LMAS functionally separates the alimentary and respiratory tracts, while the rigidity of the device facilitates quick and easy insertion.In comparison to other supraglottic airway devices, numerous studies have shown the LMAS to have improved outcomes in the pediatric population (1)(2)(3)(4)(5).Unfortunately, most of these studies have been comparative data with small sample sizes, reporting oropharyngeal leak pressure, ease of insertion, and the feasibility of gastric access and mechanical ventilation.The goal of our study was to build upon this foundation with a large sample size while focusing on LMAS use at a major tertiary children's hospital.To accomplish this goal, a retrospective audit of a large cohort of clinical anesthesia providers in our tertiary children's hospital was conducted over a two-year period.Various performance indices of the LMAS were measured by this descriptive retrospective audit.

METHODS
Following approval by our Institutional Review Board (IRB), we searched our hospital's electronic medical record database (Epic EMR, Verona, WI, USA) to identify all children in whom the LMAS was utilized for airway management between October 4, 2010 and October 11, 2012, regardless of the surgical procedure or anesthetic approach.Given the retrospective nature of the study, informed consent was waived by our IRB.Of note, during the study period additional LMAS sizes (1.5 and 2.5) were introduced by the manufacturer for clinical use.We collected the following demographic data: age, gender, weight, American Society of Anesthesiologists (ASA) physical status classification, type of anesthesia provider and type of surgery.We collected the following LMAS data: size of the LMAS, the number of insertion attempts, volume of air injected into the cuff, the cuff pressure, and the oropharyngeal leak pressure.We also recorded the performance of tests for proper position, the mode of lung ventilation, the use of muscle relaxants and the use of any alternative airway devices.The oropharyngeal leak pressure, obtained by closing the adjustable pressure limiter (APL) valve and auscultating for air escaping from the mouth, was recorded.The oropharyngeal leak pressure was not measured in all children.Data analysis was performed using Microsoft Excel (Redmond, WA, USA).The primary outcomes were first-attempt and overall placement success rates.Secondary outcomes were: oropharyngeal leak pressures, frequency of manufacturer-recommended tests for proper position, failure rate, and complication rate.
For standard references, we relied on the manufacturer's recommendations for deflation of the LMAS prior to insertion, weight-based selection of initial size, and cuff volumes and pressures (6).Successful placement of LMAS was defined as documentation of any one or more of the following: adequate chest rise upon initial manual ventilation, maintenance of normal saturation, a leak pressure adequate for the surgical procedure and mechanical ventilation, a positive suprasternal notch test (gel test) or passing of a gastric tube down the drain tube of the LMAS.Failure of insertion was defined as documentation of having to change the LMAS size to achieve adequate leak pressure and/or conversion to an alternative airway device.Leak pressure measurement was obtained by closing of the adjustable pressure limiter (APL) valve and auscultating for air escaping from the mouth.

RESULTS
Of the 75,614 general anesthetics delivered during the study period, 10,499 (13.9% ) included an LMA device.The distribution of the different LMA devices used is shown in Table 1.The LMAS was used in 418 children, accounting for only 4% of all LMAs and 0.6% of all general anesthetics.The LMAS devices used are further subcategorized by size in Table 2. LMAS sizes 3 and 4 were used in a total of 334/418 (80% ) of cases.The half sizes (1.5 and 2.5) were used in only 7 children.Patient demographic data is shown in ta-

DISCUSSION
The first significant finding of this audit is the high LMAS placement success rate, regardless of provider skill-level.With a first-attempt placement success rate of 96.4% , this study in a large pediatric population replicates the LMAS ease-of-use seen in the adult population.This finding reaffirms the importance of supraglottic airways, and why they play an essential role in the difficult airway algorithm.More specifically, it proves the LMAS as a device with wide implications in the hands of all providers, a finding that builds upon similar data reported by Ja-gannathan, et al (2,3).
The LMAS was overwhelmingly employed for minor surgical and radiological procedures, similar to the recommended indications for the LMA Classic or Unique.This seems to suggest that the LMAS was used as a substitute for the LMA Unique, despite its advanced features and functionalities.Our data shows that the LMAS was used for only five laparoscopic cases (1.2% ), which is significantly lower than that reported by Sanders, et al, where 13% of their LMA ProSeal cases were laparoscopic procedures (7).Our finding may therefore reflect an unspoken reluctance on the part of pediatric anesthesiologists to rely on a supraglottic airway device for laparoscopic procedures.Recognizing this concern about the use of supraglottic airway devices in laparoscopic procedures is important since it might highlight a misconception about the LMAS.The purpose and design of the LMAS is to facilitate its use in more advanced  procedures.And if it is not being used in the cases for which it was designed, we must ask why the device is not being utilized to its maximum potential.
With mechanical ventilation used in only 26% of LMAS cases, the avoidance of positive pressure ventilation is likely related to the limited use of this device for advanced procedures.The ability of LMAS to provide effective positive pressure ventilation has been demonstrated by Verghese C, et al (1) and Hosten T, et al (8) with the LMAS and ProSeal LMA in adult patients.In our study, the oropharyngeal leak pressure measured in 90 cases was on average 20.8 cm H2O.This is similar to previously reported data (2,3), but greater than the values reported in a study that compared the LMAS with the Igel (9).Leak pressures were in the 20-25 cm H2O pressure range for sizes 3 and 4, values that are consistent with those reported by Jagannathan, et al (3,4).Mean leak pressures for size 2 were 17.2 cm H2O, which is slightly less than the 19.3 cm H2O reported by Jagannathan, et al (2).Sizes 1.5 and 2.5 had mean leak pressures of 18 and 17 cm H2O, respectively.Despite these discrepancies, these pressures were sufficient for effective positive pressure ventilation in those patients in which this ventilator mode was utilized.If usage of the LMAS can be encouraged in more complex cases, we suspect that the use of mechanical ventilation with the LMAS will proportionally increase too.The demographic data demonstrates that the LMAS was used primarily in older children, with the average age being 12 years old.As a device capable of use in even the neonatal population with a high success rate, we would have hoped for a younger median age (10)(11)(12).This might simply reflect a lack of experience with the LMAS in younger patients by anesthesia providers or some general unwillingness to utilize supraglottic airways in younger patients.Nonetheless, this aspect of LMAS utilization requires further investigation for a better understanding of the device.
The relationship between cuff volume and pressure has important implications in regards to adverse events related to LMAS placement (13).With LMAs associated with a 50% post-operative sore throat rate, and other much less common adverse events such as nerve palsy, dysphagia, and airway edema, it is important to understand cuff volume and its relation to cuff pressure (14).As highlighted by Bick et al, the recommended cuff pressures are not the ideal cuff pressures, nor do the cuff volumes correlate well to a cuff pressure.Looking for instances of cuff over-inflation, our data shows that recorded cuff volumes were much less than those recommended by the manufacturer (15).A possible reason for these low cuff volumes is that many clinicians at our institution insert the LMAS directly out of the packaging without deflating the cuff or empirically inflating the cuff to achieve an adequate seal.This practice at our institution appears to prevent over-inflation of the cuff, something that has been reported to occur with over 70% of LMA (16).Cuff under-inflation may itself be associated with suboptimal performance of the LMAS.
The LMAS is safe for use in pediatrics.Only five of 418 (1.2% ) insertions were reported as failures.For three of the five, the leak was significant enough to warrant a change in LMAS size.Two of the five were known complications in our study.One patient developed airway activation shortly after insertion and vomited.The LMAS was removed and the patient was promptly intubated.No particulate material or gastric content was noted when the endotracheal tube was suctioned.Gross blood-staining of the LMAS was reported in another patient due to traumatic insertion.The overall low incidence of LMAS complications may also be attributed to low adverse event reporting.
The limitation of this audit is the fact that that LMAS sizes 3 and 4 accounted for the majority of cases in this study and no patient required a size 1 LMAS.In addition to this, sizes 1.5 and 2.5 were utilized in very few cases (n= 7) since these sizes were not available for clinical use until a few months prior to the conclusion of this review.This study did not attempt to investigate user preference or why certain LMA devices were utilized.Also, in addition to being a retrospective study without postoperative follow-up, this was a single-site study and our findings may not necessarily reflect practice in other clinical settings or institutions.
In summary, this study shows the LMAS to be a highly successful and reliable device, regardless of user experience.Our audit shows that the LMAS was rarely used for more invasive surgical procedures or in young children and infants, despite its advanced features and functionality.The recommended tests to ensure proper positioning were rarely performed by providers.Further studies into the etiology of user LMA preference along with studies of the LMAS in difficult airways are needed to continue our understanding of the practical utilization of second-generation supraglottic airway devices in the pediatric population.
This was a non-funded research project.Values reflected in table are number (percentage) or mean (SD).

Table 1 .
Description of LMA Airway Devices Used.table are number (percentage).

Figure
Figure.Laryngeal Mask Airway Supreme.
One of the authors (PO) serves as a Consultant for Teleflex Medical, Inc., maker of the laryngeal mask airway.None of the additional authors of this study have any disclosures.
table are mean (SD) range.
2. The number of attempts at placement was documented in 396/418 (95%) of cases.The firstattempt success rate at placement was 96.4% (382/396), and the second and third-attempt success rates were 100% .Five of 418 (1.2% ) insertions were reported as failures.Of the 5 failed insertions, the LMAS was replaced with a different size in 3 patients and with an endotracheal tube in 2 others.A vast major of the cases were general superficial procedures such as minor general sur- Laryngeal Mask Airway Supreme in Children Nobuyuki-Hai Tran et al. ble