Guest Post: Supraglottic Airway Devices Should Be Your First Line

This is a guest post written by Jeff Poland, NRP, FAWMc, FACPMc, for the Great EMS What-If-We’re-Wrong-A-Thon. I have a lot of experience in prehospital and perioperative airway management, and on every other day of the year am a stark proponent of the use of supraglottic airway devices only as a rescue airway in emergency situations – almost (around 99.9999999999999% of the time) never as a first line. But, below outlines the best reasoning I can come up with for why:

Supraglottic Airway Devices Should Be Your First Line

While endotracheal intubation has long been touted as the gold standard for airway securement, increasingly we are seeing more and more services and geographic areas move away from endotracheal intubation (ETI) in favour of first line placement of a supraglottic airway (SGA), with the option of ETI if the SGA fails. This is a prudent and much-needed step in the right direction for the following reasons:

Several studies [1,2] have indicated that prehospital intubation has a very low success rate. Intubation is a skill which requires a great deal of practice, and has no correlation with the experience that a paramedic has [3]. In other words, if you don’t do the skill a lot, you aren’t very good at it, and I think that is something that we all can agree on. With most of fire-based EMS, and a lot of third service EMS, focusing on a 5:1 paramedic:patient ratio [4], and the already low frequency of patients requiring this delicate procedure, which, if it fails, is catastrophic for the patient, most paramedics, especially in those systems, simply do not get the required amount of practice to remain proficient.

One of the main concerns regarding airway management is that the airway needs to work. SGAs are dislodged only minimally, and rarely are placed wrong [5]. When your patient needs an airway now, you should just put in a SGA and not have to worry about it any more. An old co-worker of mine once told me “why would I use an ET tube when this (the King Airway) is easier, quicker, and I absolutely know it’s in?” High-stress situations such as cardiac arrest and unconscious/unresponsive patients often have providers anxiety levels up, and an unrecognized oesophageal intubation is almost universally lethal. On the other hand, I have had one endotracheal intubation using a King Airway, and that required 45 minutes, a low profile MAC 3, an airway manikin, and a set of long Magill forceps. (Beth Lattone, of the Community College of Aurora’s Paramedic Program, if you’re reading this, this definitely was not on one of your airway heads, so I don’t even know why I brought it up.)

Supraglottic airways have also been shown to provide some measure of protection against vomiting [6]. This has been shown to be similar to that provided by cricoid pressure, a recognized mainstay in every emergency and failed airway algorithm, although it is much easier to use an SGA than it is to use cricoid pressure. Given that they can protect the airway up to 120cmH2O of pressure, tell me again how ETI is the gold standard?

Furthermore, the King LT has been shown to be equal to ETI in cardiac arrest, and the authors also claim that because of the more rapid airway control, it could be considered superior [7]. Instead of mucking around with trying to get a good laryngoscopic view during cardiac arrest, why not just pop in the SGA and not have to worry about it later on?

ETI is an old skill. Technology is increasing, and making things both better and easier for the provider. Why are some people so focused on keeping the old technology and refusing to adapt to the changing world? So many physicians have gone on record saying that they don’t support paramedics intubating, we continue to have abysmally high failure (and worse, unrecognized oesophageal intubation) rates, and those are time and cost consuming to fix. More and more paramedic programs are getting away with 5 simulated intubations, period, in order to pass, and it sounds like we are rapidly recognizing that ETI in the prehospital setting needs to go the way of the dodo. Even anaesthesiologists are using more and more SGAs for more and more cases. Isn’t it about time we get on board with these changes, and leave ETI for the docs who want to stay outdated?

While those are some compelling arguments against endotracheal intubation, I still firmly maintain my view that SGAs are a second-line intervention when ETI fails. Want to find out why? Join myself and my esteemed colleague Benjamin Dowdy on 21 June 2015 while we debate this issue live. For any further questions or comments, I can be contacted at jeff.poland@gmail.com.

References

1. http://informahealthcare.com/doi/abs/10.1080/10903120902935280
2. http://emj.bmj.com/content/22/1/64.full
3. http://www.rochestergeneral.org/~/media/Images/Imported/gedownload/etisuccessrate.pdf
4. https://www.auroragov.org/cs/groups/public/documents/document/019791.pdf
5. http://circ.ahajournals.org/cgi/content/meeting_abstract/122/21_MeetingAbstracts/A52
6. http://journals.lww.com/anesthesia-analgesia/Abstract/2008/02000/A_Comparison_of_Seal_in_Seven_Supraglottic_Airway.15.aspx
7. http://www.sciencedirect.com/science/article/pii/S0300957204000103

Challenging Tradition: Better Precordial Lead Placement

This post is part of a series presenting challenges to the traditions of EMS.

Challenging Tradition: Better Precordial Lead Placement

Application of the precordial electrodes for a 12-Lead ECG is a process steeped in over 75 years of tradition. Drs. Wolferth and Wood first described the usages of additional chest leads for the diagnosis of myocardial infarction using the leads IV, V, and VI in 1932[1] and by 1938 the standard nomenclature and position of the V-leads was described in a joint paper from the American Heart Association and the Cardiac Society of Great Britain and Ireland[2].

Since 1938, there has been little focus in validating the classical precordial lead placement. Instead, efforts to improve the sensitivity and specificity of the 12-Lead ECG focused on adding new electrodes[3,4,5] or improving existing morphological and ST-segmental criteria[6].

In 1971, the concept of body surface potential mapping (BSPM) was introduced as an alternative to the standard 12-Lead ECG [7], and by the 1980's it was recognized as providing larger gains in sensitivity in acute myocardial infarction detection over the usage of the classical precordial leads[8]. However, BSPM relies on expensive recording and post-processing techniques, and is cumbersome in its requirement for a large electrode vest which envelops the chest of the patient.

Figure 1: 80-Lead body surface potential mapping locations.

In 1985 the first paper on improving the positions of the precordial leads using BSPM was introduced by Drs. Kornreich et al[9]. They explored electrode locations which provided higher degrees of sensitivity and specificity than the traditional precordial lead placement and continued their research into 2008 with a paper describing 4 additional leads which could be added to the traditional 10 electrodes to provide information similar to that of a BSPM[10].

Research in 2002 by Drs Kors and Herpen found that moving only two precordial electrodes (V4 and V6) was required to transform the 6 precordial electrodes into a viable interpolated BSPM[11]. Their paper was notable in it sought to find the minimal derangement of the classical positioning in order to obtain diagnostic results.

In 2007 and 2008, Drs. Finlay et al explored alternative precordial lead placement using a data driven approach which sought to improve the sensitivity and specificity of MI, LVH, and other ECG abnormalities[12,13]. As with prior research, they proved again that the classical precordial lead positions perform poorly when compared to interpolated BSPMs, however, they acknowledged their improved lead positions were not practical in clinical application. Also of note, Drs. Finlay et al commented that any change to the precordial lead placement would be, "unlikely to succeed because the familiar format of the 12-lead ECG coupled with the considerable amount of diagnostic criteria accumulated in the literature mean that it is a tool with which most clinicians are extremely comfortable and which they are therefore unlikely to relinquish."[14]

However, in 2011, Drs. Peter Scott et al demonstrated a simple repositioning of the precordial electrodes which not only improved sensitivity and specificity of acute myocardial infarction identification, but also could be performed in a practical manner[15]. Using data derived from 80-lead BSPM tracings, they performed analysis which found the most appropriate positions of the precordial leads to be located along a horizontal line beginning from V1 and V2 and extending along to the midaxillary.

Figure 2: Optimal location of the precordial leads V1-V6 for the detection of acute myocardial infarction.

This paper has a high potential to challenge the status quo in not only pre-hospital acquisition of 12-Lead electrocardiograms but also in-hospital. The electrode positions given are simple to apply, and could provide for a lesser degree of inter-operator variability in positioning. More importantly, this optimized placement provided for a higher sensitivity and specificity across all types of myocardial infarction.

In personal correspondence with Dr. Scott, I inquired as to the changes this presented to other common uses of the 12-Lead ECG--such as bundle branch block definitions or VT vs SVT algorithms--and he related that this research served to open the door to further research into the practical clinical benefits.

• Does the evidence support challenging traditional precordial lead placement?
• What possible limitations does this lead placement present?
• What barriers exist to the adoption of this lead placement today?

References

1. Wolferth CC, Wood FC. The electrocardiographic diagnosis of coronary occlusion by the use of chest leads. Am J Med Sci 1932;183:30-35.
2. Barnes AR, Pardee HEB, White PD, et al. Standardization of precordial leads. Am Heart J 1938;15:235-239.
3. Perloff JK. The Recognition of Strictly Posterior Myocardial Infarction by Conventional Scalar Electrocardiography. Circ 1964;30:706-718. [FullText]
4. Erhardt LR, Sjogrn A, Wahlberg I. Single right-sided precordial lead in the diagnosis of right ventricular involvement in inferior myocardial infarction. Am Heart J 1976;91:571-6. [PubMed]
5. Zalenski RJ, Cook D, Rydman R. Assessing the diagnostic value of an ECG containing leads V4R, V8, and V9: The 15-lead ECG. Ann Emerg Med 1993;22:786-793. [PubMed]
6. O'Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction: A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circ 2013;127:e362-e425. [FullText]
7. Barr RC. Selection of the Number and Positions of Measuring Locations for Electrocardiography. IEEE Trans Biomed Eng 1971;18(2):125-138.
8. Kornreich F, Rautaharju PM. The missing waveform and diagnostic information in the standard 12 lead electrocardiogram. J Electrocardiol 1981;14(4):341-50. [PubMed]
9. Kornreich F, Rautaharju PM, Warren J, et al. Identification of best electrocardiographic leads for diagnosing myocardial infarction by statistical analysis of body surface potential maps. Am J Cardiol 1985;56(13):852-6. [PubMed]
10. Kornreich F, MacLeod RS, Lux RL. Supplemented standard 12-lead electrocardiogram for optimal diagnosis and reconstruction of significant body surface map patterns. J Electrocordiol 2008;41(3):251-6. [PubMed]
11. Kors JA, van Herpen G. How many electrodes and where? A "poldermodel" for electrocardiography. J Electrocardiol 2002;35 Suppl:7-12. [PubMed]
12. Finlay DD, Nugent CD, Kors JA, et al. Optimizing the 12-lead electrocardiogram: a data driven approarch to locating alternative recording sites. J Electrocardiol 2007;40(3):292-9. [PubMed]
13. Finlay DD, Nugent CD, Donnelly MP, Black ND. Selection of optimal recording sites for limited lead body surface potential mapping in myocardial infarction and left ventricular hypertrophy. J Electrocardiol 2008;41(3):264-71. [PubMed]
14. Ibid. 12.
15. Scott PJ, Navarro C, Stevenson M, et al. Optimization of the precordial leads of the 12-lead electrocardiogram may improve detection of ST-segment elevation myocardial infarction. J Electrocardiol 2011;44(4):425-431. [PubMed]