To Intubate or Not to Intubate?
Kenny Navarro // January 31, 2014
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 patients1. Moreover, early American Heart Association guidelines classified endotracheal intubation as a “definitely helpful” intervention for cardiac arrest resuscitation2.
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 intubation3. 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 course4. However, researchers in Cincinnati soon found EMT-Basics could not reliably and consistently differentiate between esophageal and endotracheal placement using traditional assessment techniques5, and success in a classroom setting did not necessarily result in high success rates in actual patients6.
In fact, researchers prematurely stopped an evaluation of endotracheal intubation success by EMT-Basics in rural Indiana due to the unacceptably high intubation failure rate7. 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 low8.
Regardless, the National EMS Scope of Practice Model did not include endotracheal intubation as a skill for the EMT or Advanced EMT levels of certification9. 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 country10. 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 arrest11. 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 infarction12. 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 alone13. Prehospital intubation is associated with increased mortality in trauma patients who present in the field with a Glasgow Coma Score of 314.
Traumatic brain injury
Prehospital intubation of patients who suffer traumatic brain injury remains controversial15. Prehospital intubation of traumatic brain injury results in higher mortality compared to emergency department intubation16,17. 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 mask18.
Prehospital intubation is associated with decreased survival in patients suffering from moderate to severe head injury19. 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 mask20.
In many EMS systems, supraglottic airways have become the rescue airways of choice because of their simplicity, speed of insertion, and efficacy21. Prehospital insertion times are not significantly different between endotracheal tubes and supraglottic airways22. 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 alone23,24.
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 SGA25.
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 ETI26.
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 significant27.
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 pressures28.
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 tachycardia29. 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 ventilation30.
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 placement31.
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 airway32. A cadaver study demonstrated wide variability among seven different supraglottic airways in their ability to seal the esophagus and prevent regurgitation33. 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 tubes34.
A radiological study of the LMA demonstrates laryngeal distortion produced by the device35. 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 airway36.
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 humans37. 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) devices38. A prehospital investigation involving two separate EMS agencies found similar results39.
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 emergencies40-42. 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 benefit43.
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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