Supraglottic airway devices are widely used in the pre-hospital environment because of their simplicity, speed of insertion, and efficacy(1). Some argue the term extraglottic airway device is more appropriate since portions of many of the devices lie below the level of the glottis(2)Regardless, and in the interest of simplicity, this article will use the term supraglottic airway device (SAD) to describe the family of orally inserted devices whose distal end lies in the hypopharynx or esophagus.
Supraglottic versus endotracheal: Which is better?
Researchers in Japan compared the effects of out-of-hospital endotracheal (ET) intubation versus the family of SADs using several survival outcome measures (3). Although more patients who were intubated achieved return of spontaneous circulation (ROSC) in the field and survived long enough to get to the emergency department, there were no differences in the devices in survival to hospital admission, one-month survival, or neurological outcome at one month.
In a nationwide population-based observational study involving more than132,000 cases of out-of-hospital cardiac arrest, researchers found the odds of having favorable neurological outcome one month after the arrest were slightly higher for patients who received pre-hospital ET intubation when compared to use of a supraglottic device, although the authors did not feel the difference between the two groups was clinically significant (4). Together, these studies suggest use of the SADs does not place patients who suffer out-of-hospital cardiac arrest at a disadvantage for long-term survival.
Development of the SAD
One of the first SADs to come on the market was the Laryngeal Mask Airway (LMA), invented by an anesthesiologist named Archie Brain in England (5). Brain was attempting to find a hands-free approach to ventilation that did not involve inserting a tube into the patient’s trachea. He reasoned if he could move the bag-mask seal from the face to the laryngeal inlet, he could ventilate the patient effectively using low pressure. After development and cadaveric testing of several prototypes, Brain successfully used the device on a patient undergoing general anesthesia.
The first two reported cases of LMA use in the pre-hospital setting involved patients trapped in vehicles following a vehicle collision (6). In both cases, vehicle damage made it impossible for paramedics to visualize the glottis. Blind insertion of the LMA allowed the rescue crews to successfully ventilate the patients during extrication.
Easier to train with the SAD
Researchers found medical and paramedical student first-attempt success rates were significantly higher for LMA rather than for ET tube placement (7). In addition, the researchers detected end-tidal carbon dioxide levels about 50 seconds sooner with the LMA, suggesting earlier effective ventilation with the LMA. Other researchers have demonstrated that EMS personnel can provide ventilation through an LMA that is as effective as ventilation through an ET tube (8).
SAD side effects and adverse outcomes
In the rare instance when the LMA fails to secure the patient’s airway, however, the complication rate is quite high. Using data from both ambulatory and nonambulatory anesthesia settings, researchers found more than 62 percentof the adult patients with LMA failure developed significant adverse respiratory events such as desaturation, hypercapnia, or increased peak inspiratory pressures (9).
In a similar study involving pediatric patients undergoing general anesthesia at a tertiary care academic medical center, researchers found the LMA failure rate (defined as replacement of the LMA with an ET tube) to be 0.86 percent, with many of these cases resulting in hypoxemia, hypotension, and tachycardia (10). A Cochrane Review of randomized controlled trials of obese participants aged 16 years and older undergoing general anesthesia found the rate of LMA failure to be about three to five percent (11). Whether pre-hospital rates of LMA failure or complications are similar remains unknown.
A meta-analysis of in-hospital use of the LMA demonstrated the incidence of aspiration associated with the device is comparable to aspiration incidence associated with face mask and tracheal tubes (12). However, one should consider this data with caution as it included in-hospital cases only where patients are prospectively screened and prepared. This is not the case for the pre-hospital environment.
Dual lumen SADs
Another early type of SAD that became popular in the pre-hospital environment is the esophageal tracheal combitube (ETC), often referred to simply as the Combitube. This device is a double-lumen tube with a proximal and a distal cuff that each have a separate inflation port. After blind oral insertion and inflation of both cuffs, ventilation is possible regardless of whether the distal portion of the tube has come to rest in the esophagus or the trachea.
Auscultation of the chest is an unreliable indicator of correct placement and experts recommend either qualitative or quantitative capnography for ventilation and correct placement confirmation (13).
Early reports of the ease of insertion and effectiveness of ventilation quickly led to its popularity. Use of the Combitube in adult patients who suffered cardiac arrest produced blood gas analysis results comparable to results obtained by using an ET tube (14). The Combitube proved to be an effective method of airway control in trauma patients with a failed intubation attempt (15). Researchers in Wisconsin could find no difference in ROSC, survival-to-hospital admission, or survival-to-hospital discharge rates between patients managed by EMTs with a Combitube or paramedics with ET tube (16).
The complexity of the double lumen, double port system and the frequent need for multiple attempts at insertion are major criticisms of the Combitube (1). Clinically, a retrospective review of pre-hospital run reports from adult patients whose airways were managed with a Combitube found the complication rate to be about 27 percent(17). These complications included the inability to place the device, dental trauma, and subcutaneous emphysema. Use of the Combitube in adult patients who suffered an out-of-hospital cardiac arrest has resulted in esophageal tears with accompanying subcutaneous emphysema, pneumomediastinum, and pneumoperitoneum (18).
Single lumen SADs
The laryngeal tube, often referred to as a King tube, simplified the design of the Combitube by using a single lumen with a single port that inflates both cuffs simultaneously. Mean placement time was significantly reduced for the King tube compared to the ET tube when inserted by emergency medicine resident physicians, fourth year medical students, and paramedic students (19). In a series of trauma scenarios, paramedics managed the simulated patient’s airway with an ET tube, a Combitube, or a King airway (20). The fastest form of advanced airway control was with the King airway. In a block randomization comparison of ET intubation versus insertion of the King tube in 13 geographically distinct EMS agencies, researchers found no significant difference in placement success or time to ventilation between the two devices, suggesting the King tube was a safe and effective airway device (21).
Despite the fact that 62 percentof King tube insertions were rated as easy, paramedics in Norway reported problems with insertion in 53 percent of the patients (22). These problems include difficulty seating the tube, vomiting and aspiration, dislodgement and the inability to auscultate lung sounds during ventilation. An evaluation of pre-hospital insertion of a King tube in two European countries found that almost 40 percent of the patients developed significant tongue swelling (23). In several of the cases, removal of the tube immediately created life-threatening complications for the patients.
Evolutionary developments of SADs
One of the most recent SADs to reach the pre-hospital environment is the i-Gel. The distal portion of the device is covered with a thermoplastic elastomer that molds to the pharyngeal and laryngeal anatomy (1). The device incorporates a gastric channel that permits decompression and suctioning of stomach contents to reduce the risk of aspiration (24). Cadaveric studies of the i-Gel demonstrate reliable and consistent supraglottic seating necessary for effective ventilation (25).
A fifty patient case series of i-Gel insertion in an operating room found first time successes placement rates of 90 percent with a mean insertion time of 11 seconds (26). Two retrospective clinical audits conducted in the United Kingdom found first time successful insertion of the i-Gel in patients who suffered out-of-hospital cardiac arrest was higher than for ET tube insertion (27). Paramedics in Southern Germany recorded 90 percent first time successful insertion rates for the i-Gel during resuscitation attempts of adults who suffered an out-of-hospital cardiac arrest (28). In addition, the paramedics rated 80 percent of the insertions as easy and could detect no ventilation leak in 80 percent of the patients.
However, in a three-patient case series involving regurgitation, the i-Gel did not adequately protect one patient’s airway from aspiration during an elective surgery, although the patient had an uneventful recovery (29). Rescuers attempting to resuscitate a young male who was the victim of drowning could not effectively ventilate the patient through an i-Gel and were forced to remove the device. Aspiration of seawater may have increased lung compliance thereby requiring ventilation pressures much higher than can be provided with the device (30). In an audit of patients who suffered out-of-hospital cardiac arrest, 59 percent had inadequate ventilation with the use of the i-Gel (31).
Over the last few decades, a new SAD appears in the literature at a rate of one per year (32). Only a few of these devices are intended for use as an emergency airway device in the pre-hospital environment. Most of the literature involves ease of use, ventilation parameters, or speed of insertion. Literature describing the effects of SAD use on clinical outcomes is sparse.
References
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