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August 1, 2013
Breathe easier: Devices that improve ventilation
During the early days of EMS development, three airway control and ventilation methods existed in the prehospital arena; head positioning with bag-valve-mask (BVM) ventilation, esophageal obturator airways (EOA), and endotracheal intubation. Early researchers demonstrated that even experienced EMTs and paramedics had difficulty providing effective ventilation when using head-positioning and the BVM (Elling & Politis, 1983).
Researchers in South Carolina found the failure rate of the esophageal cuffs in EOAs to be unacceptably high (Bass, Allison, & Hunt, 1982) while researchers in Iowa reported significant displacement of the larynx and trachea following EOA insertion (Low, Jensen, & Cavanaugh, 1982). Multiple case reports from that time reported both esophageal and gastric rupture following EOA insertion by trained prehospital crewmembers (Adler & Dykan, 1983; Crippen, Olvey, & Graffis, 1981; Harrison, Nord, & Beeman, 1980).
Experts considered the endotracheal tube as the most the most efficacious airway control device and encouraged EMS to adopt endotracheal intubation as the airway of choice for many critically ill or injured patients (Pepe, Copass, & Joyce, 1985). Moreover, early American Heart Association guidelines classified endotracheal intubation as a “definitely helpful” intervention for cardiac arrest resuscitation (American Heart Association, 1992).
Endotracheal intubation as gold standard?
Subsequently, paramedics and prehospital medical directors began accepting endotracheal intubation as the “gold standard” of airway control (Dickinson, Cohen, & Mechem, 1999) as the procedure allowed advanced providers to establish, maintain, and protect the airway from aspiration.
Endotracheal intubation also facilitates oxygenation and ventilation, prevents airflow into the stomach during BVM ventilation, provides a route for some medications when IV access is not available, and permits suctioning of the trachea and bronchi (Saunders, 2012).
A direct relationship exists between skill proficiency and skill performance (Latman & Wooley, 1980). EMS personnel are more successful with skills they perform on a regular basis. In order to remain proficient at tracheal intubation, an expert panel on airway management at the Proceedings of the Guidelines 2000 Conference for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care recommended that every paramedic within an EMS system perform at least 10 out-of-hospital intubations each year (Barnes et al., 2001). The panel further recommended that the agency delivering EMS should provide considerable retraining for any paramedic who could not meet that minimum standard.
Evidence suggests that the yearly mean average for paramedics may be half that amount and that 40% of medics may not have an opportunity for endotracheal intubation in any given year (Wang et al., 2005).
A variety of airway devices
Given that the efficacy of tracheal intubation is questionable, the high incidence of misplaced tracheal tubes, and the low frequency of intubation per individual medic, many EMS systems are searching for alternative airway control devices. The ideal device would be easy to place by every medic in the system, even those that may not often treat many critical patients. The device would also have to be safe for patients and must provide ventilation that is at least equal to the tracheal tube.
Supraglottic airway devices
The most common advanced airway used alternatively to endotracheal intubation belongs to a group called supraglottic airways. There are many varieties of supraglottic airway devices (SAD) however, there are only four basic categories; laryngeal masks, laryngeal tubes, double-lumen tubes, or the miscellaneous or other SAD. One feature common to the four categories is that rescuers can insert the devices without direct laryngoscopy. This makes the devices attractive because EMS personnel find both the initial training and skill maintenance easier when compared to endotracheal intubation (Russi, & Miller, & Hartley, 2008; Russi, Wilcox, & House, 2007).
Also, since the devices do not require direct laryngoscopy, EMS personnel can insert them without having to interrupt chest compressions in patients suffering from cardiac arrest. This will increase the total amount of time that rescuers are pushing on the chest.
When properly trained, EMS personnel can safely provide ventilation that is at least as effective as ventilation provided with a bag-valve mask or an endotracheal tube (Cady, Weaver, Pirrallo, & Wang, 2009; Dörges, Wenzel, Knacke, & Gerlach, 2003; SOS-Kantos Study Group, 2009).
Recently, researchers with the Resuscitation Outcomes Consortium (Wang et al., 2012) retrospectively examined airway data from two previously published cardiac arrest outcome studies (Aufderheide et al., 2011; Stiell et al., 2011). The researchers found that adult patients who suffered an out-of-hospital cardiac arrest were about one and one-half times more likely to survive to hospital discharge with satisfactory functional status if EMS personnel inserted an endotracheal tube compared to SGA insertion. Secondary data analysis found the odds of survival were almost two times greater if EMS used a bag-valve mask (BVM) than if they used any of the advanced airways. An animal study suggests that SGA cuff inflation (even to the manufacturer’s recommendation) may cause carotid artery compression with a concomitant 15-50% reduction in blood flow to the brain when compared to ETI or no advanced airway (Segal et al., 2012).
Video assisted laryngoscopy
One important newcomer to the field of prehospital airway management is indirect fiberoptic or video-laryngoscopy. These devices permit visualization of the laryngeal structure through a view tube with a lens system or through a digital camera lens embedded in the laryngoscope blade.
Video-laryngoscopy improves glottis visualization in a manikin with the greatest improvements seen in simulated difficult airway scenarios (Aziz, Dillman, Kirsch, & Brambrink, 2009). Compared with direct laryngoscopy, video laryngoscopy improved visualization of the airway structures in patients requiring emergency airway maneuvers outside of an operation room. (Jones, Agrawal, & Schulte, 2013).
No perfect airway device
EMS personnel must be aware that no perfect airway control device exists. Each presents with its own benefits and risks. Endotracheal intubation may provide many advantages; however, the literature highlights numerous complications associated with this procedure in the prehospital environment.
Supraglottic airways are a reasonable alternative to endotracheal intubation and may reduce some of the risks of advanced airway placement seen with endotracheal tubes. Likewise, video-laryngoscopy appears to improve glottic visualization; however, there utility of that technology in the out-of-hospital environment remains unknown.
It is worth noting that no definitive evidence exists that demonstrates improved survival rates offered by insertion of an advanced airway for patients who suffered cardiac arrest (Neumar et al., 2010). When compared to bag-valve-mask ventilation, the use of any advanced airway during the resuscitation attempt from out-of-hospital cardiac arrest decreases neurologically favorable survival (Hasegawa, Hiraide, Chang, & Brown, 2013).