Supraglottic Airways: A Look From Above

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Introduction

Advanced airway management in EMS systems around the country ranges from surgical airways to laryngoscopy, either video or direct, to the use of a supraglottic airway (SGA) device. As a “blind” airway device, the King Airway has largely replaced the Combitube as the civilian and military SGA of choice due to its design and ease of use. However, over the past decade, there have been many other SGAs, particularly iterations of the laryngeal mask airway (LMA), that have come to market. It is the wide and varied options for an SGA that have necessitated this evaluation as we hope to provide guidance to EMS agencies in choosing a device for their service.

This article serves to provide a comprehensive overview of many of the current SGAs available on the market to allow an EMS system to review and possibly adopt into their system. Given the sheer volume of products on the market, we have selected a representative cohort for review in this article, but it does not represent all available devices.

Background

Airway management in the prehospital setting is a cornerstone of patient care for all level of EMS providers. Maintaining a patent airway prior to hospital arrival is one of the few life sustaining interventions that can be applied to all patient interactions. One large retrospective study identified 11.9% of EMS calls pertain to patients in respiratory distress and between 20-30% of patients require some form of airway intervention.¹

Related

• Advanced Airway Choice in Out-of-Hospital Cardiac Arrest. Can the i-gel® Make a Difference in Patient Survival?
• Optimal Prehospital Airway Management Depends on EMS System Efficiency
• It’s About Paramedic Intubation Skill Maintenance, Not ETI vs. SGA

Airway interventions can include basic positioning, suctioning, application of oxygen, bag valve mask utilization with/without adjuncts including oral and nasal airways and positive pressure ventilation with more advanced techniques. These more advanced techniques include the use of SGAs, endotracheal intubation (ETI), or cricothyrotomy. Historically, ETI has been a pillar in airway management for paramedics. Over time, it has been noted that ETI success rates dramatically alter a patient’s chances at survival. The success of intubation by a prehospital provider is related to the patient’s anatomy and medical presentation, the EMS providers level of proficiency in the skill, the frequency of successful skill utilization throughout their career, and their confidence in the logistical aspects of the procedure.²

In the last 10 years, the use of prehospital intubation has increased in European countries while it has decreased in the United States. A meta-analysis showed that there is still a significant difference in successful intubation when comparing physicians to non-physician providers in the prehospital setting.² Given the challenges of patient care in the prehospital environment, there have long been considerations of a more simplified airway management approach utilizing SGAs given their many theoretical and practical advantages.

The concept of SGAs emerged in the early 1980s.³ These extra glottic devices do not violate the larynx, but instead are inserted through the oropharynx, and produce a sealed airway below the tongue but above the vocal cords. SGA types continue to expand with modifications in the materials utilized, exact sealing locations within the devices, and number/order of steps required for their placement. The SGAs ease of use, speed of insertion, predictability, and simplicity of training have made them a viable first line airway technique for unconscious patients needing airway management, back up modality to failed ETI, and subsequent alternative to ETI during airway placement for awake patients in both the prehospital and hospital setting. These devices have been proven successful in many specific medical conditions pertaining to airway management as well as in controlled and more austere environments.

Currently, the use of an SGA is within the national scope of practice for AEMTs, but in some states it is within the scope of practice for EMRs, further highlighting its simplicity and widespread usage. Due to widespread usage, there are now well over 50 subtypes of SGAs available on the market. Of these, there are a much smaller number of broad categories of SGAs including the Laryngeal Mask Airway (LMA), i-gel, King Laryngeal Tube (King LT), and Esophageal Tracheal Combitube (Combitube).

ETI has long been considered the “gold standard” of securing an airway; however, recent literature has demonstrated many advantages on the use of supraglottic devices in the prehospital setting.

Many studies cite their simplicity and ease of use.³ Pennant et al showed that first attempt success rates were higher with LMA vs ETI in medical and paramedicine students⁴ Not only have SGAs been shown to have higher first pass success, but they have demonstrated as effective ventilations as ETI.

Through this ease of use, it has been postulated that this prevents interruptions in chest compressions and the time off the chest relating to better perfusion during CPR and better neurological outcomes.² The most recent discussion on the use of SGA versus ETI has centered around two large studies: the PART Trial and the AIRWAYS-2 Trial. The PART Trial compared King LT SGA with ETI and noted significantly better clinical outcomes with King LT in the prehospital setting.⁵ This is somewhat contrasted to the AIRWAYS-2 Trial that compared i-gel to ETI and that showed no difference in outcomes.⁶ To synthesize these studies’ results, both studies noted the ease of use of SGA increased first-attempt success rates, which favors SGA use, and at least comparable patient outcomes.

It is necessary to note that most of the body of SGA research has focused on comparisons between SGA and ETI in out-of-hospital cardiac arrest. Several studies have attempted to compare BVM ventilation alone with the use of SGA, however they are retrospective registry analyses or meta-analyses and have limited findings that seem to show equivalence between BVM and SGA.⁷ There is also limited study in the setting of pediatrics. Several studies have shown them to be safe and effective, but there have been no true comparison studies. The most noted study by MA Guasche et al compared neurological outcomes of ETI with BVM in the pediatric population and found no difference.⁸

In summary, the body of evidence supports the use of SGAs as at least comparable to ETI with several studies reporting potential improved outcomes. Where the data is most robust, in comparison to ETI, is that SGAs are easier to use and are quicker to place which may contribute to findings of improved outcomes.

Product Review

– LMA Classic
o Product description
▪ This is a first generation, cuffed perilaryngeal sealer that is non-directional and non-esophageal sealing.⁹
▪ Technically, this is a reusable device with an elliptical mask using a cuff attached to a ventilation tube. The aperture bars on the mask prevent the epiglottis from obstructing ventilation. It masks the glottis with the distal tip sitting just posterior to the cricoid cartilage while the proximal portion sits against the base of the tongue. An inflation port allows for mask inflation to create an adequate seal.
o Upsides of Usage
▪ In a 1990s study, untrained nurses were able to place the LMA Classic successfully 71% of the time during cardiac arrest management during first pass.¹⁰
▪ In one study, compared to ETI, the LMA Classic can be placed markedly faster (38 seconds vs 88 seconds).¹¹
▪ During an in-hospital pediatric study, the LMA Classic was placed successfully greater than 90% of the time on first pass.¹²
▪ During an in-hospital resuscitation of over 300 neonates, the LMA Classic was placed successfully on first pass over 98% of the time without aspiration complications.¹³
▪ Compared to other SGAs there does not appear to be any increased rates of airway trauma on insertion in both adult and pediatric patients.¹⁴
o Downside of Usage
▪ Like other SGAs, the LMA Classic is not a definitive airway and because it does not seal the trachea from the esophagus, aspiration events are a possibility. However, the most common complications include poor seal, failed insertion, and need for repositioning.15 Specifically, the seal failure tends to occur at higher airway pressures.¹⁶
▪ Compared to other SGAs, the LMA Classic does not allow for insertion of a gastric tube or specifically facilitate ETI through the device.
o Durability
▪ Moderate durability given the reusability with stability similar to LMA Proseal. However, there are not multiple tether locations which may make it more difficult to secure the airway with either tape or commercial tube securing device.
o Pediatric Usage
▪ Multiple sizes are available. Specifically, pediatric sizes are available and easy to purchase.

– LMA Fastrach (FT LMA)
o Product description
▪ This is a second generation, cuffed perilaryngeal sealer that is directional and non-esophageal sealing.⁹
▪ FT LMA, or better known as the intubating LMA, utilizes a more rigid airway tube, a tracheal tube ramp, and larger internal diameter to allow for up to an 8.0 specially made ETI tube to be placed blindly into the trachea after LMA placement. The inflation of the mask is identical to that of the LMA Classic.
o Upsides of Use
▪ A single prehospital trial demonstrated paramedics were able to secure ETI through the FT LMA 88% of the time compared to 63% of the time with standard intubation techniques.¹⁷
▪ In a large hospital-based study, ETI was successful over 98% of the time with FT LMA after three attempts.¹⁸
▪ During simulated cardiac arrest management, paramedic students placed the FT LMA faster and were able to ventilate quicker on first pass success than the LT.¹⁹
o Downsides of Usage
▪ No large prehospital studies have been done proving efficacy of converting to ETI through the device.
▪ The device requires a specialized endotracheal tube to facilitate subsequent endotracheal tube placement.
▪ The rate of bloodstain and mucosal edema was noted to be higher in FT LMA compared to LMA Classic and LMA Supreme.²⁰
▪ No gastric port is available on the device.
▪ There are more steps required to utilize this device as a conduit for ETI then if simply placing a SGA requiring more training and preparation by crews.
▪ Esophageal intubations have been noted through the device but are detected using standard techniques, specifically end tidal CO2 monitoring.
o Durability
▪ More stable product design with more rigid structure allowing more stability with slightly more increased tether points which make it easier to secure the airway with either tape or commercial tube securing device.
o Pediatric Usage
▪ No small pediatric sizes are available as it is only for 30kg and up and there are only three total sizes available. Sizes are easy to purchase.

– LMA Proseal
o Product Description
▪ This is a second generation, cuffed perilaryngeal sealer that is directional and esophageal sealing.⁹
▪ Utilizes a similar design as the LMA Classic with location of mask and the seal formed. Differences include its reusable status after decontamination by standard hospital cleaning techniques as well as the drainage port that allows for gastric contents to drain from the hypopharynx and theoretically reduce the amount of aspiration occurring during placement.
o Upsides of Usage
▪ Gastric port is separate from the ventilation port which is meant to allow for drainage of potential aspirates as well as for gastric tube insertion.
▪ Higher rates of seal formation compared to the i-gel for effective ventilations due to the dorsally located cuff of the device creating extra seal force.
▪ Similar oral pharyngeal leak pressures and first pass success rates and timing to both the LMA Supreme and i-gel.²¹
o Downsides of Usage
▪ No true tract available for ETI, requires either low success blind intubation or complex fiberoptic ETI.
▪ More expensive given its reusability making it potentially less ideal for prehospital operations.
▪ Flexible cuff makes it more prone to folding causing its first pass success rate to be lower than LMA Classic.²²
o Durability
▪ More durable material given its ability to be reused; however, it holds minimal tether points which make it more difficult to secure the airway with either tape or commercial tube securing device.
o Pediatric Usage
▪ Pediatric sizes are available and easy to purchase.

– LMA Supreme
o Product Description
▪ This is a second generation, cuffed perilaryngeal sealer that is directional and esophageal sealing.⁹
▪ Utilizes a similar concept to the LMA Classic with some modifications. There is a reinforced tip of the mask which prevents mask fold over and allows for seating the device extremely close to the arytenoids. There is a gastric port allowing for gastric decompression, ability of gastric contents to bypass the pharynx, and subsequently a reduced risk of aspiration.
▪ Further, the device has a semi-rigid, curved structure that allows for ease in following the contour path of the airway.
o Upsides of Usage
▪ When placed by prehospital providers on unconscious patients requiring ALS management, it had a 100% success rate.²³
▪ When placed by inexperienced military operators on over 500 patients in an operating room setting, the LMA Supreme was successfully placed on the first pass in the shortest amount of time compared to the i-gel, LMA Proseal, and King LT.²⁴
o Downsides of Usage
▪ No true tract available for ETI, requires either low success blind intubation or complex fiberoptic ETI.
▪ In some patients with abnormal anatomy, the ridged structure has been noted to be detrimental to placement and led to device failure.
o Durability
▪ Considered to be a more stable SGA during transport, specifically in austere environments given its more ridged structure via its oval airway cross section.
▪ There are multiple tether points via a built in bite block and fixation tabs are present which make it easier to secure the airway with either tape or commercial tube securing device.²⁵
o Pediatric Usage
▪ Pediatric sizes are available and easy to purchase.

– i-gel
o Product description
▪ This is a second generation, cuffless pre-shaped sealer that is esophageal sealing.⁹
▪ The i-gel’s main benefit is the lack of need to inflate the mask portion of the device. It seats similarly to the LMA style of SGAs, but its mask portion, made of thermoplastic elastomer, is meant to form an impression fit to the hypopharynx allowing for a stable seal. Intubation through the device is possible under fiberoptic guidance. It does have a gastric port in sizes except size 1.
o Upsides of usage
▪ Compared to the LMA-Proseal, the i-gel has acceptable airway sealing pressure, is easier to insert, and is less traumatic with lower incidence of sore throat. Hence, i-gel is a good alternative to LMA-Proseal.²⁶
▪ Compared to the LMA Classic, the mean duration of insertion time was 15.92 ± 1.62 s in the i-gel group versus 26.06 ± 5.12 s in the LMA Classic. However, overall comparison for time to placement did not differ amongst all different SGAs.¹²
▪ Blind intubation through the device is possible and when successful rapid; however, recommendations are to utilize fiberoptic methods to ensure proper placement.²⁷
▪ Proposed benefit in improving carotid artery blood flow given its lack of needing to be inflated for effective seal formation.
▪ It can support a gastric tube insertion on all sizes except a size 1.
o Downsides of usage
▪ There have been case reports of the i-gel melting during Helicopter EMS transports when exposed to extremely high temperatures for a significant amount of time (hours).²⁸ The manufacturer claims the melting temperature is between 200-240 degrees Celsius.
▪ Given the lack of inflation for the mask portion of the device, the i-gel does sit well within in the pharynx but is known to have less effective seal rates compared to other LMAs.²⁹ This seal rate does not improve with warming the mask prior to application.³⁰
o Durability
▪ Moderately durable design with multiple tether locations but small risk of device melting in extreme heat as documented in a case report.
▪ Sides of mask are durable and prevent folding during insertion of the device.
▪ There is a built in bite block and the i-gel manufacturer recommends the use of the included tape and/or the airway support strap as the primary means of securing the i-gel in place.
o Pediatric usage
▪ Many pediatric sizes are available and easy to purchase.

– King LT (LT-D and LTS-D)
o Product Description
▪ This is a second generation, cuffed pharyngeal sealer with esophageal cuff^.9
▪ In its basic (standard) version, the laryngeal tube is made up of a tube with a larger balloon cuff in the middle (oral pharyngeal cuff) and a smaller balloon cuff at the end (esophageal cuff). The tube is bent at an angle of 30-45° in the middle; the bend is located in the larger cuff. There are two apertures, located between the two cuffs, through which ventilation takes place. Both cuffs are inflated through a single small lumen line and pilot balloon. The cuffs are high-volume, low-pressure cuffs with inflating volume ranging from 10 ml (size 0) to 90 ml (size 5). A large bore syringe, which is marked with the required volume for each size, is used to inflate the cuffs. A cuff inflator can also be used, in which case the cuffs should be inflated to a pressure of 60cmH2O. Three black lines on the tube indicate the depth of insertion when aligned with the teeth.
o Upsides of Usage
▪ Designed to function if placed within the esophagus which leads to high success rates given the natural predilection of airways to be placed in this location. Studies have reported that it is as effective as ETI in out of hospital cardiac arrest.⁵
▪ Double lumen technology allows for placement of a gastric tube and subsequent decompression if needed. Teeth marks allow for depth measurement for accurate placement. Single inflation points for both cuffs allow for rapid securement in the airway.
o Downsides of Usage
▪ The King LT-D does not protect against gastroesophageal reflux and aspiration, but a newer model, the King LTS-D, has a gastric channel for suctioning available. Inserted at a 45 degree rotation from centerline at corner of mouth and rotated into position (per manufacturer instructions).
▪ Animal studies have shown impairment in carotid artery blood flow due to balloon inflation.³³
o Durability
▪ Studies have been performed and the device is rated to be autoclaved 50 times before being considered ineffective indicating it is made of durable equipment
▪ There is a tether point of which make it possible to secure the airway with either tape or commercial tube securing device.
o Pediatric Usage
▪ Pediatric sizes are available and easy to purchase even down to multiple newborn sizes.

– air-Q
o Product Description
▪ This is a second generation, cuffless pre-shaped sealer and non-esophageal sealer.⁹
▪ This is a single lumen laryngeal mask airway that allows for subsequent intubation through the device. Features a guide ramp within the mask to assist with proper placement of ETT and a design specifically made to assist in lifting the epiglottis out of the way.
o Upsides of Usage
▪ Color coding scheme for size makes it easier to know which size to use. Single lumen with single cuff that speeds application. May not need further inflation if monitoring balloon is “taught” after insertion.
o Downsides of Usage
▪ Gastroesophageal reflux is still possible and only one of the three models (air-Q Blocker) holds a gastric port. Cases of improper insertion of blind airway are known but you can blindly intubate through the device.
o Durability
▪ Noted to be as durable as other LMAs on the market due to the equipment utilized to produce the device and there is a single tether point of which make it possible to secure the airway with either tape or commercial tube securing device.
o Pediatric usage
▪ Pediatric sizes are available and easy to purchase.

Direct Comparison Studies

• In a simulated tactical environment, 19 paramedic students were able to place an i-gel faster than King LT. The i-gel was placed in 14 seconds vs 39 seconds for the King LT. Further, all participants preferred the i-gel.³⁴
• In a multi-year, single county EMS system of patients with supraglottic airways placed for cardiac arrest, it was demonstrated that the i-gel had a first pass success of 92% vs King LTS-D showing a first pass success of 79%. Additionally, overall success rates for both SGAs showed 90% vs 83% for i-gel and King LTS-D ³⁵
• When comparing an LMA Classic to the i-gel in difficult airway manikins, the time to successful placement for 100 nurse students was 29 seconds vs 10 ³⁶
• When comparing five different SGAs (King LTS-D, LMA Supreme, air-Q, i-gel, and Combitube) in their ability to produce negative intrathoracic pressure during simulated cardiac arrest with an impedance threshold device placed, the King LTS-D and Combitube did not seal the airway in a manner to generate or maintain negative intrathoracic pressure.³⁷

Discussion

Given the wide range if supraglottic airways on the market and the continued advancement of the technology, it can be technically challenging to evaluate all the options and recommend only one type of SGA for an EMS system. Therefore, this is not a comprehensive review, but we endeavored to review many of the most popular products on the market and offer considerations for the evaluation process. Furthermore, much of the research that provides the foundation of such a recommendation is limited to evaluating single or a few types of SGAs.

This minimizes the applicability of the data. We also acknowledge the unique aspects of each department and that there are unique resource and implementation considerations that must be factored. We evaluated the SGAs based on several factors that we felt were important to a system: ease of use, speed of placement, availability of multiple sizes, gastric port availability, ETI possible through the SGA, price, and durability.

One of the most important factors for an EMS system to consider is the familiarity of a device and the “learning curve” required to implement new devices. Products that involve multiple ports and balloons (i.e. combitube) tend to take more time to apply and involve several steps. This naturallycincreases the learning curve for implementation on a system-wide basis and can also lead to application errors.

A further favorable aspect of an SGA is adaptability to various patient sizes. Many products do offer various sizes and pediatric applications. Sizing an airway can be a challenge in the prehospital setting and various methods of sizing have been devised from weight based and height based algorithms. Device sizes are coded by color or numerically labeled for use.

Another major factor is cost. Cost goes beyond just the cost of the device and includes the durability and shelf life of the device as well as the cost of training to implement a new device. Cost must further be considered in the setting of frequency of use and therefore, department specific volumes must be taken into consideration as well as overall budgets.

Ultimately, balancing all of these factors in relation to the needs of a specific EMS system will provide the best choice. Care should be taken to ensure that the process for product evaluation is patient centered and assures the safety of products is considered.

Recommendation

After comprehensive review of the literature we have noted there to be a large variety of SGAs available for utilization in the prehospital setting. After filtering down to the most common devices and most popular devices on the market and performing a more in depth review, we noticed a few small differences that might make a few devices superior to implementation into an EMS system.

The LMA Classic is a first generation SGA and its largest problem for an EMS system is its lack of tether points and possible durability issues. The LMA Proseal is a reusable device making it more expensive and therefore potentially less ideal for EMS usage where sterilization may not be readily available. Further, LMA FT requires an increase in purchasing material given the need for a specific ETI tube to perform ETI through the device.

The Combitube is more complex to place given the need to inflate multiple balloons and it has less available sizes making it less ideal. This leaves four devices that offer different aspects of clinical care. The LMA Supreme is relatively easy to place and is durable with a gastric port, but it requires very complex devices to perform ETI through the device. The King LT is a longstanding pillar of EMS care and while it may not excel in any aspect, its long term familiarity cannot be underestimated. The air-Q has only one variant with a gastric port but can facilitate ETI through blind insertion or fiberoptic methods while being durable and relatively easy to place. Finally, the i-gel allows ETI through fiberoptic techniques, is easy to use, and has a gastric port while being durable and reasonably priced. For these reasons, we think the last four devices may offer some potential advantages over the others for EMS use, fully understanding that local consideration is needed.

In summary, we have noted there to be a large variety of SGAs available for utilization in the prehospital setting. When an EMS department is considering a specific SGA for their department the following considerations must be taken into account and balanced based on department specific attributes to identify the optimal device for selection. First, how rapidly can the device be successfully placed by providers? Second, is the device durable, available in multiple sizes, and have the capability to be adequately secured during an often chaotic prehospital environment?

Third, is there a mechanism for some form of ETI through the device to assist in definitive airway management? Fourth, does the device mitigate the risk of aspiration with advanced technology? When looking at these four questions, a department can arrive at a device that fits their specific needs.

Editor’s note: This manuscript was updated on April 7, 2021, with clarifications from the authors.

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