Evolution of Airway Intubation Device Designs and Advancement

---

Starting with a title of “evolution,” readers may think they are about to have another history lesson on airway devices, but this is not a history lesson. This article serves as a guide to how we as anesthesiologists have arrived at our current technology, and it also provides thoughts on the next areas for development. It is important to approach any topic with a biodesign mentality.¹ The fundamental belief of biodesign is that a product should be produced from a “need.”

Meeting Needs

The earliest airway devices were made to facilitate visualization of the airway and vocal cords,² driven by surgical needs to deal with laryngeal pathology. The need to visualize the larynx for tracheal intubation did not come until later when the ability and need to ventilate a patient became possible. Tracheal intubation was not described until 1913, not much more than 100 years ago. If you look at the device used in 1913, you will appreciate that it has not come far in development in over 100 years. As the practice of anesthesia grew from open drop ether introduced in 1846, to cyclopropane introduced in 1933, the need for contained intratracheal administration of anesthesia became more important.

The next major advance in the consistent intubation of the trachea with a breathing tube was the Miller laryngoscope blade.³ The interested reader can look at this publication from 1941 and appreciate that the Miller blade has not changed significantly since its first description. Two years later, in 1943, Dr. R.R. Macintosh realized a need for a laryngoscope blade design with a curved angle to improve visualization of the larynx while causing less trauma.⁴ It is curious that after only two years since Miller described his blade design, Macintosh referred to the Miller blade as the “standard laryngoscope.” As many clinicians have experienced, direct laryngoscopy (DL) with the typical Miller or Macintoshblade will not intubate all individuals, and thus arose the need for additional devices to manage the difficult airway.

Solving Standard Geometry

Clinicians and medical technology (medtech) inventors have since realized the inability to intubate the trachea using the “standard geometry” Miller or Macintosh blades. The past 70 years have seen a collection of devices developed to solve the difficult intubation situation. While the gold standard for the anticipated difficult airway still may be awake fiberoptic intubation, this procedure requires time, user skill and training, patient compliance, and for many reasons, it may not be the procedure of choice. Many options that came to market as useful alternatives to DL have fallen out of favor after the introduction of the video laryngoscope (VL) around 2001. The data have been very convincing that the success of the VL is far superior to DL.^5,6 In addition, VLs increase the frequency of successful intubations as well as decrease laryngeal trauma and hoarseness. However, even with the VL, users who are not trained in DL or VL do not have the same level of intubation success.⁵ The advent of the VL has seemed to eliminate many other advanced airway devices, while the use of DL continues to linger as the method of choice for uncomplicated intubations. Let’s return to the medtech inventor who is considering the needs for the next best solution for intubation. The “needs statement” for this next inventor might consider various “must-have” items on their list, such as perfect first-pass success, ease of use, low cost and nontraumatic use. The same medtech inventor might like other “like-to-have” items on their list, such as minimal training and low environmental impact. A clinician may argue that most of these needs are already met by the VLs currently on the market. From the clinician’s point of view, the difference in VLs is minor and success may only come down to user comfort and experience.

Innovating Intubation

Now, what is the next step in medtech innovation for tracheal intubation? It seems that the VL market is saturated with similar devices that are relatively expensive compared with DL. The next medtech innovator might consider the needs that are missing from the current VL market. A list of “must-have” statements on the next development front needs to consider 1) ease of use, 2) decreased learning curve, 3) lower cost and 4) ease of use outside the OR.

What do all these laryngoscopes have in common? Ultimately, they represent a continuation of the same approach our field has used for over a century—the manual use of tools to obtain a view of the larynx so that the clinician can manually advance a styleted (or bougie-guided) endotracheal tube into the airway—albeit with some new bells and whistles. Along with the warranted and common love of the VL, this has led to stagnation in airway device innovation despite the ongoing unmet needs from complex airways and inexperienced providers. One may rightly ask whether this is the final frontier of airway management.

The average academic anesthesiologist may believe the intubation issue has been solved because there are not many airways that can’t be overcome with current technology in experienced hands. Most intubations are still accomplished with DL even if VL has shown to be more successful and cause less patient trauma.⁵ The anesthesia community is a conservative group and has been slow to adopt new technologies, which will always be a challenge for innovators trying to make advancements in the field. Currently, it appears that technology for intubation becomes more complicated with more expensive options while solving a diminishing problem in the OR.

Moreover, airway management is not exclusively an anesthesiology practice. A 2017 Cochrane review noted that success of intubation did not improve with VL when considering inexperienced users.⁵ The inexperienced or occasional user might be the hospital intensivist, ER physician, paramedic or emergency medical technician. When it comes to airway management, there are several things that distinguish this group of caregivers from anesthesiologists in the OR. Compared with the wide assortment of devices and adjuncts in the OR, there are typically many fewer items available outside the OR. Conditions are not controlled, and patients are physiologically unstable and have limited reserve, thus reducing the time available to complete airway management before hypoxia occurs. Relative to an anesthesiologist, the inexperienced or occasional VL operator lacks the same level of baseline training, daily repetition, detailed knowledge of airway anatomy, and experience with distorted anatomy and airway pathology.

The anesthesiologist who practices frequent intubations obtains a unique body of knowledge of the anatomy of the larynx, and repetition leads to advanced hand–eye coordination to explore and expose the laryngeal anatomy. Years of clinical experience better inform device and tube size selection to further increase first-pass success rates and reduce airway trauma. The VL does not solve the gaps in anatomic knowledge and hand–eye coordination of the untrained or less practiced caregiver. Thus, the logical course for medtech innovation is exploration of a solution for failed intubations outside the OR, in lower-resource settings with inexperienced providers, and that is where the next needs statement should be directed. The needs statement for this development would be less requirement for advanced training, limited requirement for hand–eye coordination and no requirement for knowledge of airway anatomy. One consideration that might fulfill these requirements would be a “blind” intubation technique such as through a laryngeal mask airway, or with a device such as the Trachlight (Laerdal Medical).⁷ The rapid advancement of machine learning/artificial intelligence may deliver a device that also solves this need, but current complexity and cost may slow adoption outside the hospital.⁸

For the non-anesthesiologist emergency airway provider, airway management is likely to be one of several emergency skill sets that must be maintained in the absence of frequent performance clinically. For these providers, a device that is simple to operate, user-friendly, and requires minimal advanced training and hand–eye coordination would be ideal. This would reduce the burden of training and maintenance of skills on occasional airway providers. It is well described that the stress of a high-stakes, time-pressured emergency impairs cognitive and motor performance.⁹ Partial mitigation of these deleterious effects on human performance by a simply designed and intuitive device might also improve success rates.

Conclusion

A discussion of the consequences of failed intubation is also warranted, as it applies to both expert and nonexpert airway providers. The ultimate step in a cannot-intubate/cannot-oxygenate (CICO) scenario is emergency front-of-neck access (eFONA). Emergency cricothyrotomy performed by anesthesiologists has a high failure rate and is a complex procedure that most anesthesiologists expect to perform rarely, if ever, during their career.¹⁰ The psychological stress and time pressure inherent in a CICO scenario further complicate successful performance of eFONA.¹¹ Maintenance of this skill set requires a self-motivated clinician to attend periodic training workshops, which offer deliberate practice on porcine or 3D-printed models. There is evidence of skills deterioration within a period of several months, suggesting that yearly training is required to maintain competency.¹² For the busy anesthesiologist, this may be impractical, and unfortunately these skills deteriorate from lack of use and practice. For the occasional airway provider, maintenance of this skill set is even less likely, and skill decay occurs as quickly as three months after training.¹³ All these factors paint a bleak picture for clinicians who find themselves in a CICO scenario.

However, the good news, as Chrimes et al put it, is that “de novo occurrence of a CICO event … is the exception rather than the rule.”¹¹ Instead, alveolar oxygen delivery is typically initially successful via mask or supraglottic ventilation, but subsequently is lost after repeated attempts at airway instrumentation. As airway trainers ourselves, we have seen firsthand how difficult it is to transmit the expertise of our field to the novice airway manager. This fact further highlights the need for a device capable of achieving a near-perfect first-pass success rate, independent of operator experience, that will establish an airway durable enough to eliminate additional instrumentation. Such a device could be employed outside the OR to minimize airway trauma until transport to an OR location with experienced anesthesiologists, advanced airway equipment and surgical airway backup for definitive management. The device also could be used by anesthesiologists in the unanticipated difficult airway situation to rapidly establish ventilation and temporize while waiting for advanced equipment and additional resources. In such a future, we may take another large step toward considering airway management a “solved problem.”

References

1. Zenios S, et al. Biodesign: The Process of innovating Medical Technologies. Cambridge University Press; 2015.
2. Burkle CM, et al. Anesthesiology. 2004;100(4):1003-1006.
3. Miller RA. Anesthesiology. 1941;2:317-320.
4. Macintosh RR. Lancet. 1943;241(6233):205.
5. Lewis SR, et al. Br J Anaesth. 2017;119(3):369-383.
6. Ruetzler K, et al. JAMA. 2024;331(15):1279-1286.
7. Hung OR, et al. Can J Anaesth. 2006;53(1):107-108.
8. Wu YH. Anesth Analg. 2024 Feb 21.
9. Kelly FE, et al. Anaesthesia 2023;78(4):479-490.
10. Cook TM, et al. Br J Anaesth. 2011;106(5):617-631.
11. Chrimes N, et al. Br J Anaesth. 2020;125(1):e38-e46.
12. Chang SS, et al. Korean J Anesthesiol. 2018;71(4):289-295.
13. Turner JS, et al. AEM Educ Train. 2023;7(4):e10900.

Copyright © 2024 McMahon Publishing, 545 West 45th Street, New York, NY 10036. Printed in the USA. All rights reserved, including the right of reproduction, in whole or in part, in any form.