A significant cause of preventable prehospital deaths is failure to adequately control the airway. In the early days of EMS development in the United States, there were very few airway control techniques available to prehospital care providers. Endotracheal intubation was the primary technique used to manage unsecure airways in an emergency department, and some EMS pioneers encouraged the fledgling EMS industry to adopt endotracheal intubation as the airway of choice for many critically ill or injured patients. Moreover, early American Heart Association guidelines classified endotracheal intubation as a “definitely helpful” intervention for cardiac arrest resuscitation.
Background on prehospital endotracheal intubation
In 1994, the United States Department of Transportation added an 18-hour optional module to the National Standard curriculum that would permit, with proper oversight, EMT-Basic providers to perform endotracheal intubation. Researchers in Los Angeles demonstrated that EMT-Basic providers could achieve endotracheal intubation first-attempt success rate of 94 percent on manikins immediately following a 4-hour training course. However, researchers in Cincinnati soon found EMT-Basics could not reliably and consistently differentiate between esophageal and endotracheal placement using traditional assessment techniques, and success in a classroom setting did not necessarily result in high success rates in actual patients.
In fact, researchers prematurely stopped an evaluation of endotracheal intubation success by EMT-Basics in rural Indiana due to the unacceptably high intubation failure rate. Despite these early failures, adding qualitative colorimetric end-tidal carbon dioxide detectors eliminated tracheal tube misplacement by EMT-B providers, although first-time success rates in actual patients was still low.
Regardless, the National EMS Scope of Practice Model did not include endotracheal intubation as a skill for the EMT or Advanced EMT levels of certification. The National Scope of Practice model does not specifically prohibit states from allowing EMTs to perform endotracheal intubation; however, the psychomotor skill and associated cognitive requirements are not part of the EMS Education Standards for the country. States who wish to add this skill to locally certified EMTs must prepare the curriculum and develop competency standards.
Cardiac arrest and endotracheal intubation
Despite early support for endotracheal tube insertion, the American Heart Association acknowledges the lack of conclusive evidence demonstrating improved survival resulting from advanced airway insertion for adult victims of cardiac arrest. The need for endotracheal intubation in the field is an independent predictor of mortality in patients suffering cardiac arrest secondary to ST-segment elevation myocardial infarction. After controlling for initial arrest rhythm and other confounding variables, endotracheal intubation attempts in adult patients who suffered an out-of-hospital cardiac arrest were associated with increased mortality when compared to the use of a bag-valve mask alone. Prehospital intubation is associated with increased mortality in trauma patients who present in the field with a Glasgow Coma Score of 3.
Traumatic brain injury
Prehospital intubation of patients who suffer traumatic brain injury remains controversial. Prehospital intubation of traumatic brain injury results in higher mortality compared to emergency department intubation.[16,17] A propensity-matched study of traumatic brain injury with a Glasgow Coma Score less than 8 found significantly higher adjusted mortality rate and worsened admission oxygenation for patients intubated in the field before arrival in the emergency department compared to those receiving oxygen by mask.
Prehospital intubation is associated with decreased survival in patients suffering from moderate to severe head injury. A review of the National Pediatric Trauma Registry examined over 31,000 pediatric patients with severe brain injury and found no survival benefits offered by prehospital intubation when compared to ventilation with a bag-valve mask.
In many EMS systems, supraglottic airways have become the rescue airways of choice because of their simplicity, speed of insertion, and efficacy. Prehospital insertion times are not significantly different between endotracheal tubes and supraglottic airways. With proper training, EMS personnel using supraglottic airways can provide ventilation that is at least as effective as ventilation provided with a endotracheal tube or bag-mask used alone.[23,24]
In an evaluation of over 3,300 patients who suffered an out-of-hospital cardiac arrest, researchers in Japan could not demonstrate statistically significant differences in neurologically intact survival rates between patients managed with an endotracheal tube or an SGA.
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 SGA or paramedics with ETI.
A three-year review of the out-of-hospital cardiac arrest cases conducted in Japan found that patients managed with an endotracheal tube were only slightly more likely to have better neurological function one month after the arrest when compared to patients managed with a supraglottic airway. Although the difference reached statistical significance, the researchers did not believe the difference was clinically significant.
Some have questioned the safety of supraglottic airway devices. Researchers conducting an observational study in Michigan found that although the incidence of laryngeal mask failure (defined as rescue endotracheal tube placement following laryngeal mask removal) was low, more than 62 percent of the patients with laryngeal mask failure developed significant adverse respiratory events, which included desaturation, hypercapnia, or increased peak inspiratory pressures.
In an evaluation of over 11,000 pediatric patients undergoing general anesthesia, laryngeal mask airway failure (defined as replacement of the LMA with an endotracheal tube) occurred in one out of every 117 patients (0.86 percent), with many of these patients developing hypoxemia, hypotension, and tachycardia. After introducing the laryngeal tube to the management of out-of-hospital cardiac arrest, rescuers reported problems with insertion in almost 53 percent of the patients, despite the fact that 62 percent of the insertions were rated as “easy.” The problems included proper initial tube seating in the supraglottic space, leakage, vomiting and aspiration, dislodgment, and an inability to auscultate lungs sounds during ventilation.
One potential hazard that could develop with the use of a laryngeal tube comes with inadvertent tracheal placement. Should that happen, the tube would completely occlude the airway and prohibit effective ventilation. However, in a manikin study involving 500 placements facilitated by the use of a laryngoscope, rescuers did not have one tracheal placement.
One oft-cited potential hazard associated with supraglottic airways is aspiration despite proper placement of the device. One case report describes projectile vomiting over a distance of 1.2 meters in a patient with a properly placed laryngeal mask airway. A cadaver study demonstrated wide variability among seven different supraglottic airways in their ability to seal the esophagus and prevent regurgitation. 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.
A radiological study of the LMA demonstrates laryngeal distortion produced by the device. Using a swine model of cardiac arrest, researchers demonstrated that inflating the cuffs to the manufacturer’s recommendations on several types of SGAs resulted in carotid artery compression with a concomitant 15-50 percent reduction in cerebral blood flow when compared to ETI or no advanced airway.
However, magnetic resonance imaging of a human patient with a properly placed laryngeal tube failed to reveal any vascular distortion, suggesting that the artery compression seen in pigs may not occur in humans. This area will require further investigation.
Non-invasive positive pressure ventilation
Finally, early use of non-invasive positive pressure ventilation (NIPPV) may decrease the need for endotracheal intubation altogether. A meta-analysis of in-hospital studies involving patients suffering from the effects of pulmonary edema demonstrated reduced mortality and reduced need for endotracheal intubation by early use of continuous positive airway pressure (CPAP) devices. A prehospital investigation involving two separate EMS agencies found similar results.
On the other hand, researchers in San Diego, Canada, and the United Kingdom could not demonstrate reduced intubation rates or mortality improvement associated with the prehospital use of CPAP in patients with acute respiratory emergencies.[40-42] Some speculate that the lack of demonstrable benefit in prehospital CPAP studies may be the result of methodology limitations rather than a true lack of benefit.
Airway control remains a top priority in the prehospital management of critically ill and injured patients. Endotracheal intubation is a definitive method of airway control; however, prehospital use of this technique may come with an unacceptably high risk of complications and adverse outcomes. Supraglottic airway insertion may offer a reasonable alternative, although it may produce a different set of complications. Noninvasive positive-pressure ventilation (NPPV) may prevent the need for advanced airway placement in some patients.
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Kenny Navarro is an Assistant Professor in the Department of Emergency Medicine at the University of Texas Southwestern Medical School at Dallas. He also serves as the AHA Training Center Coordinator for Tarrant County College. Mr. Navarro serves as an Emergency Cardiovascular Care Content Consultant for the American Heart Association, served on two education subcommittees for NIH-funded research projects, as the Coordinator for the National EMS Education Standards Project, and as an expert writer for the National EMS Education Standards Implementation Team. Send correspondence concerning any articles in this section to Kenneth W. Navarro, The University of Texas Southwestern Medical School at Dallas, 5323 Harry Hines Blvd MC 8890, Dallas, Texas 75390-8890, or e-mail firstname.lastname@example.org