Charles N. Pozner
Stephen J Nelson
Introduction
Airway evaluation and management is the first priority of health care providers in an emergency, regardless if it occurs in or out of the hospital. The austere environment in which prehospital providers must function (e.g., poor positioning and lighting, disruptive surroundings, limited assistance) demands that airway care be carried out both thoughtfully and skillfully to ensure the best outcomes.
The gold standard of airway management is the assurance of adequate oxygenation and minute ventilation. Every prehospital provider must acquire and maintain the necessary skills to ensure that this goal can be achieved until arrival at the hospital, regardless of the device used or the technique employed.
Endotracheal intubation has evolved to become the most common advanced airway procedure to be employed in the prehospital setting. The incidence of difficult intubation in emergency medical services (EMS) is 11%. Studies of prehospital endotracheal intubation have reported success rates from as high as 96.6% to less than 75%. This highly variable success rate, coupled with the dire consequences of failure, has been the foundation of much discussion concerning the range of airway interventions necessary to optimize patient outcome in the prehospital setting.
The approach to airway management in EMS is no different than the ED or the OR. Chapters 1 to 3, and particularly Chapter 2, provide the framework with which to approach airway management in the prehospital setting. In this chapter, we introduce alternative airway devices available for prehospital use. These devices can be either primary airway management tools or rescue devices when endotracheal intubation cannot be performed or has failed. In 2006, the National Association of EMS Physicians published a position statement on the use of alternative airways in the prehospital setting. We discuss the devices available and their prehospital use. For discussion of surgical airways, refer to Chapter 16.
The Clinical Challenge
The goal of airway management is to establish and maintain optimal minute ventilation and oxygenation, and to minimize the risk of aspiration throughout the course of care. When a patient is conscious and spontaneously breathing, close monitoring may be all that is necessary to accomplish this goal. It is the role of the EMS provider to immediately intervene when the patient can neither maintain nor protect his or her airway, or when the patient needs assistance with oxygenation and/or ventilation.
Historically in EMS, mouth-to-mouth ventilation or placement of an oro- or nasopharyngeal airway coupled with bag-mask ventilation (BMV) have been the initial and primary methods of providing oxygenation and ventilation to the patient who is unable to sustain adequate gas exchange. Failing access to and training with more sophisticated devices and techniques, these are the only options available until either advanced providers arrive on-scene or the patient reaches the hospital.
With adequate training, placement of an endotracheal tube has traditionally been considered the next procedure attempted. In the event that a patient is not a candidate for intubation or that intubation is unsuccessful, bag-mask ventilation (BMV) retains its primary role in assisted ventilation.
The introduction of medication-assisted intubation (e.g., rapid sequence intubation [RSI]) has led EMS systems to ensure that their advanced providers are trained in the use of alternative airway devices, in addition to BMV, as a means to rescue the airway in the event intubation following paralysis and/or sedation is unsuccessful. The growth of experience with and research in the prehospital use of these alternative airway devices has led EMS medical directors to examine the use of these devices as an alternative to endotracheal intubation for advanced providers and as an alternative to BMV for basic-level providers. In their 2005 guidelines, The European Resuscitation Council recommends that if ventilation cannot be provided through an endotracheal tube, alternative airway devices should be employed for ventilation in the management of cardiac arrest. The American Heart Association guidelines are less directive, stating that their use appears to be safe.
Alternative Airway Devices
Bag-mask Ventilation
Although there is a proclivity toward the use of alternative airway devices for assisted ventilation at all EMS provider levels, expertise with BMV is essential, despite the fact that it is a difficult technique to master. In fact, proper BMV coupled with oro- and/or nasopharyngeal airways and cricoid pressure is capable of providing adequate minute ventilation in the majority of circumstances in which assisted or artificial ventilation is required, and provides a measure of protection against gastric insufflation and the aspiration of gastric contents. Improper use can increase the risk of gastric insufflation, regurgitation, and aspiration of stomach contents. More in-depth discussion of the BVM can be found in Chapter 5.
Extraglottic Devices
Supraglottic Device Class
LMA Type
Introduced in 1981 and approved for use in the United States in 1992, Brain developed the first supraglottic airway device, the laryngeal mask airway (LMA). This blindly inserted device has several advantages over mask ventilation, including ease of use and the ability to provide an airtight seal without head or mandibular manipulation.
Typical of all extraglottic devices (EGDs), supraglottic airways transfer the mask seal from the face to a supraglottic location. (Refer to Chapter 10 for details on insertion.)Although ventilation is facilitated, protection from aspiration is not as reliable as with a cuffed endotracheal tube in the trachea. Some have found that although the application of cricoid pressure after insertion of the LMA decreased gastric insufflation, it tended to hinder ventilation. Finally, improper placement resulting in inadequate mask seal and ventilation is not uncommon, particularly as facility with these devices is acquired.
Since its introduction, modifications of the LMA-type design, the introduction of other innovative EGDs (see Chapter 10) and the provision of single-use devices have broadened the opportunity for their use in EMS. For instance, Brain introduced the intubating LMA (ILMA) in 1997, a supraglottic device (SGD) that not only permitted one to rescue gas exchange, but also reliably facilitated blind intubation through the device. (See Chapter 10 for details on insertion.)
In the event that the ILMA provides adequate gas exchange in the field and transport times are short (e.g., urban EMS systems), many believe that intubation through the device should not be performed in the field and that the decision as to how best to achieve a definitive airway should be deferred to hospital arrival.
The ProSeal laryngeal mask airway (PLMA), a modification of the LMA-type design, is designed to minimize the risk of aspiration if regurgitation occurs and improve mask seal. This device incorporates a tube that passes through the mask to permit the insertion of a gastric tube to decompress the stomach and aspirate regurgitated gastric contents. Designed with a larger mask and a softer wedge-shaped cuff, it facilitates a better fit in the pharynx, and its deeper bowl provides an enhanced cuff seal due to its more anterior position. Unfortunately, the device is much more difficult to insert than other SGDs. This has prompted the introduction of a similar, yet disposable device called the LMA Supreme. This device has superior insertion and seal characteristics, and has the potential to be a substantial advance on other SGD designs (see Chapter 10, Fig. 10-3).
In summary, although the LMA was embraced more slowly by emergency medicine than anesthesia, it is now being widely employed in both emergency medicine and the prehospital setting. The American Heart Association, the American Society of Anesthesiologists, and others have advocated the use of the LMA as a rescue device in the setting of failed intubation. Refer to Chapter 10 for a list of available SGDs.
Retroglottic Device Class
Esophageal Obturator Airway
The first extraglottic airway device to be used in the prehospital setting was the esophageal obturator airway, and it is of historical interest only. Introduced in the late 1970s, this blindly inserted device, when properly positioned, placed a cuffed obturator into the esophagus. A face mask was then applied to the device to permit BMV. This device and a subsequent version, the esophageal gastric tube airway, were widely used as both primary and rescue airway devices. Many complications were reported, including esophageal rupture, aspiration, and inadvertent tracheal occlusion by the obturator. Because of its complication profile, difficulty in placement, and failure to provide adequate gas exchange, continued use of either device in modern EMS systems is to be condemned.
Esophageal Tracheal Combitube
In 1987, Frass introduced the esophageal tracheal Combitube (ETC; see Chapter 10). It is a blindly inserted, double-lumen tube with balloon cuffs to be positioned below (esophageal) and above (hypopharyngeal) the glottis, permitting ventilation through periglottic fenestrations located between the proximal and distal cuffs. Ventilation is also possible if the device is inadvertently inserted into the trachea (<5% of insertions; see Chapter 10, Fig. 10-20). Since its introduction, the ETC has become a common alternative airway device employed in EMS as both a primary and a rescue airway device because of its ease of placement, the preferred neutral cervical positioning for placement in trauma patients, and a perceived benefit of the cuffed esophageal tube in the unfasted patient. Complications associated with the use of the ETC include aspiration, pneumothorax, pneumomediastinum, airway injuries, and esophageal lacerations and perforations. Some authors recommend employing laryngoscopy to avoid trauma to the airway.
King LT airway (Laryngeal Tube Airway in Europe)
The King LT, approved for use in the United States in 2003, has been introduced into the armamentarium of airway devices available to prehospital providers. See Chapter 10 for a detailed description of this device and a discussion of the evidence with respect to its use. This device is an airway tube with a small distal balloon at the tip and a larger balloon at the midportion of the tube. Both balloons are inflated simultaneously, employing a single syringe. Like the ETC, when positioned properly, the distal balloon is located in the upper esophagus and the proximal balloon in the hypopharynx (see Chapter 10, Fig. 10-21). The King LT differs from the ETC in that it possesses superior insertion characteristics and has a single pilot balloon to be inflated, conferring an ease of use. Its disadvantage is that inadvertent tracheal placement does not permit ventilation, and there is a paucity of published evidence regarding success and complication rates.
Although there have been other devices developed, the ETC and the King LT remain the most commonly deployed EGDs in the prehospital setting in the Untied States.
Evidence
1. How common is the difficult and failed airway in EMS? As mentioned previously, the incidence of difficult or failed intubation in the operating room (OR) setting is 1.1% to 3.8% and 0.13% to 0.3% of cases, respectively (1). So, it is not uncommon to see a difficult airway even in the OR. The incidence of difficult intubation in EMS, not surprisingly, is three to ten times that seen in the OR at 11% (2). Studies of prehospital endotracheal intubation have reported success rates ranging from less than 75% to as high as 96.6% (3,4). It is this variation that has called into question the advisability of prehospital care personnel performing endotracheal intubation in general, and RSI in particular (see Chapter 25).
2. Is there a statement that identifies the most appropriate airway management devices for prehospital care workers? In 2006, the National Association of EMS Physicians published a position statement on the use of alternative airways in the prehospital setting (5).
3. How easy is it to learn how to use these devices?
BVM
Although it is often difficult to adequately ventilate patients with a BVM in the controlled environment of a hospital, it still remains the most commonly used emergency ventilation device in both the hospital and the prehospital setting. As early as 1986, Cummins et al. (6) reported that maintenance of an adequate mask seal is difficult and often requires more than one person to be effective; a luxury often not readily available in the prehospital setting. A study of emergency nurses reported a 25% skill retention rate 6 months after training (7).
Supraglottic Airways
The LMA has been found to be relatively easy to place by paramedics and other allied health professionals (8,9). Prehospital placement of an LMA in pediatric populations has also been shown to be straightforward. Although median insertion times were longer with the LMA as compared to BVM (30 seconds vs. 4 seconds), this was not considered to represent a clinically significant difference (10). In 2000, in a study of the ILMA, Levitan et al. (11) reported a 97% success rate, with a mean time to ventilation of 18 seconds and a mean time to intubation of 17 seconds in a variety of providers, including medical nonintubators and nonmedical personnel after a 60-minute training session. Dries et al. (12) reported similar ease of use in the aeromedical setting. In a review of PLMA literature, insertion success rates have ranged between 90% and 100%; however, studies included in this review were not in the prehospital environment (13).
Retroglottic Airways
Successful placement of the ETC in the prehospital setting as a primary airway device is reported to be 71% to 98%, and 64% to 100% as a rescue airway (14,15,16). In a retrospective analysis of ETC placement for failed endotracheal intubation in the prehospital setting, Calkins, Miller, and Langdorf (15) reported a success rate of 70%, and 16% of placements were tracheal. The King LT has been shown to be relatively easy to place. In a study by Russi, Wilcox, and House (17), paramedics with no previous exposure or training were able to place the King LT with 100% success in simulated trauma and medical cases. Again, the paucity of literature on the King LT obviates the possibility of discussing hazards and complications of the device.
4. Although these devices provide an adequate airway, do they protect the airway?
Supraglottic Airways
Although definitive airway protection from regurgitation and aspiration must never be assumed when employing an LMA, rates of aspiration in the anesthesia literature have been reported to be as low as 0.02%, likely related to the fasted state of operative patients (18). Stone, Chantler, and Baskett (19), in their study of 713 cardiac arrest patients undergoing assisted ventilation, reported a lower incidence of regurgitation with the LMA than with BVM (LMA 3.5%, BVM 12.4%, respectively). The design characteristics of the PLMA (e.g., tighter seal, esophageal drainage tube) have resulted in a decreased incidence of aspiration in studies comparing it to the LMA. Unfortunately, because these data are derived from animal, cadaver, or OR studies, the advantages of the PLMA in the prehospital setting can only be considered theoretical (20).
Extraglottic Airways
In Quebec, where ETC is performed as a basic-level procedure for all cardiac arrests, Vézina et al. (21) reported an aspiration rate of 17%. Although it is generally believed that the esophageal balloon confers an element of protection against aspiration, there is good evidence that the risk of aspiration with use of the ETC is at least that of the LMA. There is no literature on the aspiration rate of the King LT to permit comparisons or compute risk.
5. Can these devices be employed in trauma patients? Use of the LMA in the management of prehospital trauma patients has undergone limited study. There are conflicting reports on the safe use of the LMA in patients with cervical spine trauma. Keller, Brimacombe, and Keller (22), in a study using pressure sensors attached to the vertebrae in a stable cadaveric cervical spine model reported unacceptable posterior vertebral displacement when an LMA was employed. However, Brimacombe and Berry (23), in a fluoroscopically assessed cadaveric model using a destabilized cervical spine, reported no difference in displacement between the LMA and direct laryngoscopy. In a difficult trauma airway algorithm developed by Ollerton et al. (24), they found that placement of an LMA can be performed both effectively and safely. Although the PLMA would theoretically have an advantage over the LMA in trauma patients due to its tighter seal and esophageal drainage tube, it is best placed in the sniffing positions.
In a study of 420 head trauma patients, the Combitube was used as a rescue airway when endotracheal intubation was unsuccessful (15% of all cases). ETC insertion and ventilation were successful at a rate of 95% when employed as a rescue airway (25).
6. Are there certain situations where I should use a specific device over another? The majority of the literature addressing the use of EGDs in the prehospital environment concerns the LMA and the ETC. There is a paucity of data specific to the prehospital environment related to other devices to scientifically guide one with respect to device selection. However, most experts agree that systems ought to (a) seriously evaluate whether to promote EGD-based ventilation as a first-line device in unresponsive, apneic patients and relegate BMV to a subsidiary role; and (b) ensure that advanced life support providers have proficiency and the immediate availability of an EGD in the event that neither BMV nor endotracheal intubation is possible, particularly if medications are employed to facilitate airway management.
References
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