Review of Commercially Available Supraglottic Airway Devices for Prehospital Combat Casualty Care

PhD*,† ABSTRACTBackground: Airway obstruction is the second leading cause of potentially survivable death on the battlefield. The Committee on Tactical Combat Casualty Care lists airway optimization among the top 5 battlefield research and development priorities; however, studies show that combat medics lack access to the recommended supraglottic airway (SGA) devices. SGA devices are an alternative airway management technique to endotracheal tube intubation. Reports have shown SGA devices are easier to use and take fewer attempts to provide patent airflow to the patient when compared to endotracheal tube intubation. Military settings require a higher degree of skill to perform airway management on patients due to the environment, limited availability of equipment, and potential chaos of the battlefield. Finding the optimal SGA device for the military setting is an unmet need. The International Organization for Standardization describes basic functional requirements for SGA devices, as well as patient configurations and size limitations. Beyond that, no SGA device manufacturer states that their devices are intended for military settings. Materials and Methods: We conducted a market review of 25 SGA devices that may meet inclusion into the medics’ aid bag. The company’s official “Instructions for Use” document, Google Scholar, and FDA reports were reviewed to obtain information for each SGA device. Results: Twenty-five commercially available SGA devices are explored from manufacturer online sources. A commercially avail- able device list is shown later in this paper, which provides the device’s features, indications, and contraindications based on the manufacturer’s product information documentation. Conclusions: There are a variety of devices that require further testing to determine whether they should be included in sets, kits, and


Airway Management on the Battlefield
Airway obstruction is the second leading cause of potentially survivable death on the battlefield. 1 Airway management, which is critical in resolving airway obstruction, is the process of inserting a tube or device through the mouth and providing assisted breathing to the trachea. Data from the REACH study showed an underutilization of advanced airway management in the prehospital, combat setting during the early phases of the Iraq war. 2 Additionally, high mortality has been associated with advanced airway management in the prehospital combat setting. 3,4 More recent data establish that treating airway obstruction, together with respiratory compromise and noncompressible truncal hemorrhage, are the key foci to improving survival in prehospital combat casualty care. 5,6 The Committee on Tactical Combat Casualty Care (CoTCCC) lists airway optimization among the top 5 battlefield research and development priorities, but meaningful technological advances remain elusive. 7,8 TCCC guidelines recommend an early emphasis on the King Laryngeal Tracheal (KingLT™) and a more recent emphasis on the use of the i-gel™ devices. These devices and others like it are called supraglottic airways (SGAs).
In 1988, Dr Archie Brain developed the laryngeal mask airway (LMA), which provides a seal on the opening of the trachea in order to provide airflow. This device is considered the first SGA device, and many devices with the same purpose have been developed since. 9 Previously, cricothyrotomy, a surgical airway technique in which an incision is made through the cricothyroid membrane, was used to provide airflow to patients in prehospital combat settings. 10 Schauer et al. found comparable clinical outcomes for cricothyrotomy versus SGA device placement in combat settings, suggesting that SGAs may be a viable alternative to surgical airways, which are fraught with low success and high complication rates. 11,12 Another commonly used airway technique is endotracheal intubation (ETI), which requires an endotracheal tube (ETT) to be inserted into the trachea in order to provide airflow. It, too, has variable success in the hands of prehospital combat medical personnel. 2 Several studies, in a civilian setting, have shown SGAs to have advantages in ease of use, speed, safety, and number of attempts to secure airflow when compared to ETI. [13][14][15][16][17][18] Another study has compared the firstattempt insertion success rate of different SGA devices by operators with a military background. The study found a higher success rate with the LMA Supreme, i-gel, and LMA ProSeal compared to the Laryngeal Tube Suction-D and the SLIPA airway. 19 However, there is little objective information on SGA use in the actual military setting.
This paper provides a scoping review of SGA devices with a focus on specifications, technical features, and adverse reports relevant to prehospital combat casualty care. To date, there is no comprehensive review of SGAs as they relate to the military combat setting. The collection of specifications for SGA devices provides information that will improve the decision-making process for combat medical personnel procuring and using SGA devices. Additionally, our information can be used by manufacturers to improve SGA devices in terms of military use. This study identifies the need and recommends further investigation and testing of SGA devices for use in a military combat environment.

SGA Design
The original SGA device, the LMA classic, is shown in Supplementary Figure S1. The LMA classic exhibits an inflatable cuff, inflated by the inflation line and valve. The cuff is attached to the airway tube where the air source is attached to the proximal connector. SGA devices are typically manufactured as disposable (one-time use), but some models can be bought as reusable versions. Furthermore, commercially available SGA devices are categorized by the first or second generation.

First-Generation SGA Devices
First-generation devices are simple airway tubes with no gastric channels. Most first-generation devices are of the same shape and design as the LMA classic; they have inflatable cuffs connected to an airway tube with little to no additional features.

Second-Generation SGA Devices
Second-generation devices are defined by having design features to reduce the risk of aspiration, such as gastric channels. 20 These devices often have other advanced features, such as bite blocks (tough sections of the material designed to withstand the force of a bite) and ETT channels (conduits for ETTs to pass into the trachea). The LMA Protector is a second-generation SGA device, having gastric channels, and is shown in Supplementary Figure S2. During use, the patient may regurgitate gastric acid from the stomach. The gastric acid will flow up the esophagus and may lead to pulmonary aspiration, which can result in morbidity and even mortality. 21 Design developments have led to gastric channel incorporation into second-generation SGA devices to provide an effective route for gastric acid away from the larynx of the patient.

SGA Compared Anatomy
SGAs are inserted through the mouth into the larynx and provide a seal on the opening of the trachea. In comparison, oropharyngeal airway devices are inserted into the larynx but do not provide a seal. ETTs require insertion further down the airway into the trachea. Finally, nasopharyngeal airways are placed just above the epiglottis, the upper part of the larynx.

Military Combat Casualty Care Need
Combat medics provide combat casualty care in conditions where little to no light is available, using bulky and heavy equipment, while in the middle of combat chaos. The amount of space available in the combat medic's aid bag also limits the medic's ability to provide combat casualty care. It is easy to infer that airway management, already a difficult and complex prehospital procedure, takes a higher degree of skill in a military environment compared to a civilian setting. Therefore, since SGA devices are known for their ease of use, low number of attempts to use successfully, and speed of use when compared to ETI, SGA devices should be studied and tested to determine the optimal inclusion in combat medic's aid bag.
The military environment affects the decision of the optimal SGA device for inclusion in a combat medic's aid bag. Currently, there is no military-grade SGA device; SGA devices have not been tested under military standard testing (MIL-STD-810 H) to test the devices against the environmental conditions the devices are likely to experience in their lifetime. Current SGA devices have been designed and manufactured for civilian settings and not for the battlefield, military conditions. There is a need, therefore, to test the commercially available SGA devices to determine which available device can handle the military setting the best.

METHODS
All information was generated on a web-based approach. The International Organization for Standardization (ISO) was used as a reference for information on the design standards of SGA devices. The list of commercially available SGA devices was compiled through a literature search on Google Scholar (Google Inc.; Mountain View, California USA) as well as an online search using Google. Google Scholar indexes research articles and abstracts from most major academic publishers and repositories worldwide, including Pubmed, Elsevier, WorldCat, etc. Information on each device was obtained from the company's official "Instructions for Use" or "Product Information" document. If information was missing from these documents, a Google Scholar search was completed in an attempt to find the missing information. The FDA Manufacturer and User Facility Device Experience database were used to compile adverse reports for each device. Keywords used to compile the list of SGA devices include: "supraglottic airway device," "oropharyngeal airway device," "laryngeal device," "supralaryngeal device," and "extraglottic device." Google and Google Scholar Boolean operators were used as necessary. Devices were included if they met the criteria of a SGA device, a device that provides a seal on the opening of the trachea and is capable of acting as a passageway for ventilation. 22 One author (G.B.C.) performed the search and generated the list of devices. Two authors (D.J.Z. and C.N.B.) reviewed the list of selected devices to ensure that they met the criteria for SGA device. Two authors (M.N.G. and S.J.S.) obtained the information on each device, and 2 authors (D.J.Z. and C.N.B.) reviewed the information obtained. The search resulted in the selection of 25 SGA devices.

RESULTS
Tables I shows a list of commercially available SGA devices found through a web-based search, a search through commercially available online means. Lists of devices were found through various articles, from users, and manufacturer websites. Table I also provides basic information, including manufacturer, country of manufacturer, reusability, the number of available sizes, and if intubation is required. Other information recorded was if each device included specific features, such as a gastric chamber and an inflatable cuff. The indications and contraindications listed by the manufacturer are shown in Tables II and III. Additionally, the manufacturer's website and other publications used to obtain data for an SGA are included in Table II. Select devices are shown in Supplementary Figures 1-6. Air-Q Blocker Indicated as a primary airway device when an oral endotracheal tube (OETT) is not necessary or as an aid to intubation in difficult airway situations. It is especially suited for applications when a bite block and/or access to the posterior pharynx and upper esophagus is desired.
https://cookgas.com/air-q-blocker/ Air-Q ILA The air-Q is indicated as a primary airway in applications that do not require an endotracheal tube. It is also especially suited as an aid for intubation in difficult airway situations when an OETT is desired.
https://www.salterlabs.com/anesthesia/airways/ air-q-intubating-laryngeal-airways.html AuraGain LM The Ambu AuraGain is intended for use as an alternative to a face mask for achieving and maintaining control of the airway during routine and emergency anaesthetic procedures.
The AuraGain may be used where unexpected difficulties arise in connection with airway management. The device is intended for use as a conduit for an endotracheal tube in cannot intubate-cannot ventilate situations, as well as situations where is it necessary to place an endotracheal tube after insertion of the AuraGain.
The device is not intended as a replacement of an endotracheal tube and is best suited for use in surgical procedures where tracheal intubation is not deemed necessary.
The AuraGain may also be used to establish a clear airway during resuscitation in profoundly unconscious patients with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation. https://www.ambu.com/airway-management-and-anaesthesia/laryngeal-masks/product/ambu-auragain-disposable-

laryngeal-mask
Aura-I LMA The Ambu Aura-i is intended for use as an alternative to a face mask for achieving and maintaining control of the airway during routine and emergency anaesthetic procedures in patients evaluated as eligible for a supraglottic airway or in situations where other attempts to establish an airway have failed.
The Ambu Aura-i may be used where unexpected difficulties arise in connection with airway management. The device is intended for use as a conduit for an endotracheal tube in cannot intubate-cannot ventilate situations, as well as situations where is it necessary to place an endotracheal tube after insertion of the Aura-i. The mask may also be preferred in some critical airway situations. The Ambu Aura-i may also be used to establish a clear airway during resuscitation in profoundly unconscious patients with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation.
https://www.ambu.com/airway-management-and-anaesthesia/laryngealmasks/product/ambu-aura-i-disposable- The Ambu AuraOnce is intended for use as an alternative to a facemask for achieving and maintaining control of the airway during routine and emergency anaesthetic procedures in fasted patients.
The Ambu AuraOnce may also be used where unexpected difficulties arise in connection with airway management.
The mask may also be preferred in some critical airway situations. The Ambu AuraOnce may also be used to establish a clear airway during resuscitation in profoundly unconscious patients with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation.
https://www.ambu.com/airway-management-and-anaesthesia/laryngeal-masks/product/ambu-auraonce-disposablelaryngeal-mask AuraStraight Intended for use as an alternative to a facemask for achieving and maintaining control of the airway during routine and emergency anaesthetic procedures in fasted patients. The Ambu AuraStraight may also be used where unexpected difficulties arise in connection with airway management.
The mask may also be preferred in some critical airway situations. The Ambu AuraStraight may also be used to establish a clear airway during resuscitation in profoundly unconscious patients with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation.   The LMA ProSeal TM is indicated for use in achieving and maintaining control of airway during routine and emergency anesthetic procedures in fasted patients using either spontaneous or positive pressure ventilation. It is also indicated for securing the immediate airway in known or unexpected difficult airway situations.
The LMA ProSeal TM is not indicated for use as a replacement for the endotracheal tube and is best suited for use in elective surgical procedures where tracheal intubation is not necessary.

LMA Supreme
The LMA Supreme is indicated for use in achieving and maintaining control of airway during routine and emergency anesthetic procedures in fasted patients using either spontaneous or positive pressure ventilation.
It is also indicated for use as the rescue airway device in CPR procedures, in which the LMA ProSeal, LMA Classic, or the LMA Unique have traditionally been used. The LMA Supreme is also indicated as a "rescue airway device" in known or unexpected difficult airway situations. The LMA Supreme may be used to establish an immediate clear airway during resuscitation in the profoundly unconscious patient with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation.
It may also be used to secure an immediate airway when tracheal intubation is precluded by the lack of available expertise or equipment or when attempts at tracheal intubation have failed.

Air-Q Blocker
The air-Q Blocker is contraindicated in patients at high risk for regurgitation and/or aspiration. This includes, but is not limited to, patients undergoing major thoracic or abdominal surgery, patients who are nonfasted, morbidly obese, pregnant >14 weeks, or suffer from delayed gastric emptying or esophageal refl ux. Users must weigh the benefits of emergency airway needs with the potential risk of aspiration in these patients. air-Q Blocker's should be used in unconscious or topically anesthetized patients only.

Air-Q ILA
The air-Q is contraindicated in patients at high risk for regurgitation and/or aspiration. This includes, but is not limited to, patients undergoing major thoracic or abdominal surgery, patients who are nonfasted, morbidly obese, pregnant >14 weeks, or suffer from delayed gastric emptying or esophageal reflux. Users must weigh the benefits of emergency airway needs with the potential risk of aspiration in these patients. air-Q's should be used in unconscious or topically anesthetized patients only. AuraGain • Patients who have not fasted (including those cases where fasting cannot be confirmed).
• Patients who have had radiotherapy to the neck involving the hypopharynx.
• Patients with inadequate mouth opening to permit insertion.
• Patients representing for emergency surgery who are at risk of massive reflux, such as acute intestinal obstruction or patients having been injured shortly after ingesting a substantial meal.

Aura-I LMA
The device is not intended as a replacement of an endotracheal tube and is best suited for use in surgical procedures where tracheal intubation is not deemed necessary. In patients with severe oropharyngeal trauma, the Aura-i should only be employed when all other attempts to establish an airway have failed. The Ambu Aura-i is not recommended to be used in: • Patients who have not fasted (including those cases where fasting cannot be confirmed).
• Patients with inadequate mouth opening to permit insertion.
• Patients who have had radiotherapy to the neck involving the hypopharynx.
• Patients representing for emergency surgery who are at risk of massive reflux, such as acute intestinal obstruction or patients having been injured shortly after ingesting a substantial meal. The Ambu Aura-i does not protect the patient from the consequences of regurgitation and aspiration. Ambu Aura-i should only be used in patients who have been clinically evaluated by a clinician familiar with anesthesia as eligible for a laryngeal mask or in a situation where other attempts to establish and airway have failed. When the Ambu Aura-i is used in profoundly unconscious patients in need of resuscitation or in an emergency patient with a difficult airway situation (i.e., "cannot intubate, cannot ventilate"), there is a risk of regurgitation and aspiration. This risk must be carefully balanced against the potential benefit of establishing an airway (see the guidelines established by your own local protocol). The Ambu Aura-i should not be used for resuscitation or emergency treatment of patients who are not profoundly unconscious and who may resist insertion. AuraOnce The device is not intended for use as a replacement of the endotracheal tube and is best suited for use in surgical procedures where tracheal intubation is not deemed necessary. In patients with severe oropharyngeal trauma, the Ambu AuraOnce should only be employed when all other attempts to establish an airway have failed. The Ambu AuraOnce is not recommended to be used in: • Patients who have not fasted (including those cases where fasting cannot be confirmed).
• Patients with inadequate mouth opening to permit insertion. • Patients who have had radiotherapy to the neck involving the hypopharynx.
• Patients representing for emergency surgery who are at risk of massive reflux, such as acute intestinal obstruction or patients having been injured shortly after ingesting a substantial meal. The Ambu AuraOnce does not protect the patient from the consequences of regurgitation and aspiration. Ambu AuraOnce should only be used in patients who have been clinically evaluated by a clinician familiar with anesthesia as eligible for a laryngeal mask airway. When the Ambu AuraOnce is used in profoundly unconscious patients in need of resuscitation or in an emergency patient with a difficult airway situation (i.e., "cannot intubate, cannot ventilate"), there is a risk of regurgitation and aspiration. This risk must be carefully balanced against the potential benefit of establishing an airway (see the guidelines established by your own local protocol). The Ambu AuraOnce should not be used for resuscitation or emergency treatment of patients who are not profoundly unconscious and who may resist insertion.  • The airway device is not proven to protect the airway from the effects of regurgitation and aspiration. The risk of regurgitation and aspiration must be weighed against the potential benefit of establishing an airway. LM Portex Soft Seal N/A LMA Solus N/A LMA Classic 1. Patients who have not fasted, including patients whose fasting cannot be confirmed. 2. Patients who are grossly or morbidly obese, more than 14 weeks pregnant or emergency and resuscitation situations or any condition associated with delayed gastric emptying, or using opiate medication prior to fasting.
The LMA Classic is also contraindicated in: 3. Patients with fixed decreased pulmonary compliance, or peak inspiratory pressure anticipated to exceed 20 cm H2O, because the device forms a low-pressure seal (approximately 20 cm H2O) around the larynx. 4. Adult patients who are unable to understand instructions or cannot adequately answer questions regarding their medical history since such patients may be contraindicated for LMA ClassicTM use. 5. The LMA ClassicTM should not be used in the resuscitation or emergency situation in patients who are not profoundly unconscious and who may resist device insertion. LMA CTrach N/A LMA Fastrach 1. Nonfasted patients, including patients whose fasting cannot be confirmed and in other situations where there may be retained gastric contents. 2. Patients who are, more than 14 weeks pregnant, or those with any condition associated with delayed gastric emptying, or using opiate medication prior to fasting. 3. Patients with fixed decreased pulmonary compliance, such as patients with pulmonary fibrosis or because the peak airway inspiratory pressures are anticipated to exceed 20 cm H2O. When passing a fiberoptic bronchoscope (FOB), it should not be passed through the LMA FastrachTM airway aperture unless protected by the ETT. Otherwise, the FOB tip may be damaged by contact with the epiglottis elevating bar. 4. When selecting seal pressure for the LMA FastrachTM ETT, an intracuff pressure measuring device should be used in conjunction with the Minimal Occluding Volume or Minimum Leak techniques. Cuff inflation should be monitored regularly to a "just seal" pressure. Any deviation from the selected seal pressure should be investigated and corrected immediately. 5. The use of aerosolized local anesthetic agents has been associated with the formation of pin holes in LMA FastrachTM ETT SU cuffs. 6. Use only ventilators or anesthesia equipment with standard 15-mm connectors to ensure secure connection with the LMA FastrachTM ETT connector. Always ensure that the connector is securely seated in the breathing circuit to prevent disconnection during use. 7. Three-way stopcocks or other devices should not be left inserted in the inflation valve for extended periods of time. The resulting stress could crack the valve causing the cuff to deflate. 8. Laryngeal spasm may occur if the patient becomes too lightly anesthetized during surgical stimulation or if bronchial secretions irritate the vocal cords during emergence from anesthesia. If laryngeal spasm occurs, treat the cause. Only remove the device when airway protective reflexes are fully competent. 9. Do not pull or use undue force when handling the inflation line or try to remove the device from patient by the inflation tube as it may detach from the cuff spigot. 10. If airway problems persist or ventilation is inadequate, the LMA FastrachTM should be removed and an airway established by some other means.
(continued)  11. Store the device in a dark cool environment, avoiding direct sunlight or extremes of temperatures. 12. Used device shall follow a handling and elimination process for bio-hazard products in accordance with all local and national regulations. 13. Ensure all removable denture work is removed before inserting the device. 14. Gloves should be worn during preparation and insertion to minimize the contamination of the device. 15. The LMA FastrachTM is not indicated for use as an alternative to the ETT. 16. Clinicians must weigh the theoretical risk against the benefits of establishing an airway with the LMA FastrachTM in patients in whom cervical spine motion is undesirable. 17. Only use with the recommended maneuvers described in the instructions for use.

LMA Flexible
Due to the potential risk of regurgitation and aspiration, do not use the LMA Flexible TM as a substitute for an endotracheal tube in the following elective or difficult airway patients on a nonemergency pathway: 1. Patients who have not fasted, including patients whose fasting cannot be confirmed. 2. 2. Patients who are grossly or morbidly obese, more than 14 weeks pregnant or emergency and resuscitation situations or any condition associated with delayed gastric emptying or using opiate medication prior to fasting. The LMA Flexible TM is also contraindicated in: 3. Patients with fixed decreased pulmonary compliance, or peak inspiratory pressure anticipated to exceed 20 cm H2O, because the device forms a low-pressure seal (approximately 20 cm H2O) around the larynx. 4. Adult patients who are unable to understand instructions or cannot adequately answer questions regarding their medical history since such patients may be contraindicated for LMA Flexible TM use. 5. The LMA Flexible TM should not be used in the resuscitation or emergency situation in patients who are not profoundly unconscious and who may resist device insertion.

LMA Guardian N/A LMA Proseal
Due to the potential risk of regurgitation and aspiration, do not use the LMA ProSeal TM as a substitute for an endotracheal tube in the following elective or difficult airway patients on a nonemergency pathway: • Patients who have not fasted, including patients whose fasting cannot be confirmed.
• Patients who are grossly or morbidly obese, more than 14 weeks pregnant or those with multiple or massive injury, acute abdominal or thoracic injury, any condition associated with delayed gastric emptying, or using opiate medication prior to fasting. The LMA ProSeal TM is also contraindicated in: • Patients with fixed decreased pulmonary compliance, such as patients with pulmonary fibrosis, because the airway forms a low-pressure seal around the larynx. • Patients where the peak airway inspiratory pressures are anticipated to exceed 30 cm H2O with LMA ProSeal TM .
• Adult patients who are unable to understand instructions or cannot adequately answer questions regarding their medical history since such patients may be contraindicated for use with LMA ProSeal TM . LMA Protector LMA Protector™ must not be used in the case of the following: • Patients who have had radiotherapy to the neck involving the hypopharynx as there is risk of trauma and/or a potential failure to seal effectively. • Patients with inadequate mouth opening to permit insertion. • Patients presenting for emergency surgery who are at risk of massive reflux due to such conditions as acute intestinal obstruction or ileus or patients who have been injured shortly after ingesting a substantial meal (but see above under Indications for Use). • Patients requiring head or neck surgery where the surgeon will be unable to gain adequate access due to the presence of the device.  There are various types and generations of SGA devices available on the market, but none are military grade or claim to be useful for combat casualty care in military settings. Manufacturers do not provide useful specifications for the military setting, such as weight, dimensions, or the ability of the devices to operate in extreme environments and chaotic conditions. The standard SGA sizing chart based on the patient's weight and age is listed in Table IV. The sizing table is meant to provide an approximate reference for all devices.
Supplementary Table S1 sorts the FDA Adverse Reports by category for each SGA device. "Cuff Inflation/Deflation Issue" includes any issue causing the cuff of the device to leak, fail to inflate, or fail to deflate. "Difficult to Insert Properly" includes reports in which the device requires multiple attempts to insert or insertion cannot be completed. "Damage to the SGA" includes any damage to the SGA outside of the cuff area. This includes punctures to the airway tube, pieces of the ventilator connector breaking off, seals failing, or a complete break of the airway tube. "Injury to Patient" includes any negative effects experienced by the patient, which may have been caused by the SGA, after a procedure. This includes hoarse voice, damage to the vocal cords, or damage to any nerves in the airway. "Foreign Body" includes any incident in which a piece of the SGA broke off and was later found in the patient. "Miscellaneous Adverse Reports" includes issues with labeling and using other airway devices with the SGA.

DISCUSSION
While TCCC guidelines emphasize the King LT and i-gel, there are many SGA devices available on the market. Additionally, there is little data guiding these decisions beyond expert opinion. The information gathered in this paper provides useful information for a quick comparison of SGA devices in a civilian setting, but there are features important for a combat environment that are not available via an online search. These devices should be durable, easy to use, and quick to insert. In comparison with ETI, SGAs have advantages in ease of use, speed, safety, and the number of attempts to secure airflow. Also, SGAs have comparable outcomes to cricothyrotomy, which has high complication rates, meaning SGAs can be an alternative to other commonly used airway methods.
While some of the SGA devices have been evaluated with military personnel in a trial setting, further research is required to determine optimal devices for a combat setting. In the studies by Studer et al., 28 predeployment soldiers were trained with the King LT, and all but 1 were able to successfully use the device. 23 In Hensel et al., 285 military personnel were trained to use the LMA Supreme and King LT. 24 The King LT was rated better than the LMA Supreme in terms of success rate, insertion time, ability to judge correct placement, and degree of difficulty. In Nicole et al., 44 emergency department personnel evaluated the LMA Unique, King LT, and the i-gel in terms of successful placement. 25 The trial found the i-gel had a higher success rate than the LMA Unique, which had a higher success rate than the King LT. A post hoc analysis on airway management provided at the point of injury on the battlefield highlights the differences between a civilian and combat setting. 26 The analysis concludes that airway management solutions need to be optimized based on battlefield injuries rather than patients in cardiac arrest, which is the majority in a civilian setting. Therefore, while trial studies can provide useful clinical information, more information is required to determine the optimal devices.
The adverse effects from Supplementary Table S1 show issues that have been reported for SGA devices. The devices reported the most are the LMA Supreme (122), LMA Proseal (96), and the LMA Classic (50). The devices with the most cuff inflation/deflation issues are the LMA Proseal (64), LMA Supreme (49), and LMA Classic (42). Furthermore, insertion issues were seen most in the King LT (13), LMA Supreme (7), and the AuraStraight (6). While cuff and insertion issues are crucial in a battlefield environment, adverse reports alone are not indicative of one device being better than another.

MFG REQUIREMENTS AND STANDARDS
The ISO is an international organization comprised of multiple bodies whose function is to develop and publish standards. A product that has an ISO certification has proof that it adheres to specific guidelines and whose design and functioning possess a certain degree of reliability. 27 ISO standards for medical devices focus mainly on their design and manufacture. ISO 11,712 describes the essential requirements needed for the design of any supralaryngeal airways and connectors. It is important to note that supralaryngeal device is another designation for SGA devices and, therefore, ISO 11,712 is applicable to the devices evaluated in this paper. 28 This international standard defines dimensions, basic properties, and the procedure for the size designation of the airway devices.

Operation
The standard dictates that the device should be able to perform its function when the patient is in the supine position, and the head and neck are at neutral positions. Also, the device should also provide air patency when the patient's head and neck are at least ±30 • in the following configurations. Shown in Supplementary Figure  In addition, the device should also allow for air circulation in the following positions, shown in Supplementary Figure  S3: • Trendelenburg's position (whole body inclined 10 • , with head pointing down). • Sitting (torso and legs having 45 • of separation).
In terms of dimensions, ISO 11,712 states that the size of an SGA should range from sizes 0 to 6, with 0 being the smallest and 6 being the largest. Also, the smallest increment in between sizes should be 0.5. The transition number from pediatric to adult should be 3. It is important for devices used in a combat setting to follow the standard in order to minimize usage difficulties. However, some devices, such as the air-Q models, do not follow the standard sizing chart but instead follow their own arbitrary sizing. Some devices reach a maximum size below 6, such as the i-gel, which maxes out at size 5, but is approximately the same size and fits the same patient demographics as size 6 devices. In addition to the ISO sizing, the manufacturers are permitted to decide the maximum size of the devices that can fit through the tubing. These devices can include but are not limited to tracheal tubes, suction catheters, fiberoptic scopes, and bougies, among others. 29

CONCLUSION
There are currently 25 SGA devices on the market. All are FDA registered, but no devices are specifically designed with military features in mind. While the information gathered in this paper is useful for quick comparisons of SGA devices in a civilian setting, efforts are being made to understand how best the device can be adopted in combat within a prehospital setting. With the ease of use and quick insertion of SGAs, an optimal device can be crucial on the battlefield. This paper should be used to inform further research to determine optimal SGAs for use in a combat casualty care setting. Future research should be focused on user feedback, military testing, and clinical outcomes.