Ultrasound Confirmation of Endotracheal Tube Placement

Written by: Maurice Hajjar, MD (NUEM PGY-2) Edited by: Alex Ireland, MD (NUEM PGY-4) Expert commentary by: John Bailitz, MD

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Introduction

Although the cuff is inflated and the laryngoscope is removed, no emergent intubation is complete without first confirming the correct placement of the endotracheal tube (ETT). A variety of indicators exist that can confirm ETT placement into the trachea rather than the esophagus—chest rise, condensation in the tube, auscultation of breath sounds, lack of abdominal breath sounds, visualization with a video or fiberoptic laryngoscope, and both quantitative waveform capnography and qualitative (or colorimetric) capnometry. 

However, situations exist in which these techniques may be unavailable, impractical, or can even fail or mislead providers. A hectic cardiac arrest scenario may present the perfect storm. Chest compressions preclude providers from visualizing chest rise. Gastric contents or blood can mask tube condensation or preclude visualization of the cords with a video laryngoscope. Colorimetric capnometry can have low sensitivity in patients without a palpable pulse and can also be falsely positive if exposed to blood or gastric contents [1]. The sensitivity of quantitative waveform capnography decreases significantly in cardiac arrest as it requires adequate pulmonary circulation which may be absent in this or other low flow states [2,3]. Furthermore, despite increasing use, it may be unavailable at the institution altogether [4]. 

Taken together, there is a relatively high risk of esophageal intubation in this scenario which bears disastrous consequences. Any single method of confirming ETT placement is imperfect; as such, there is room for unique modalities in emergent intubations. 

Using Point of Care Ultrasound to Confirm Endotracheal Tube Placement

Why it works

Point of care ultrasound (POCUS) is readily available in emergency departments (EDs) and intensive care units in most settings and both intensivists and emergency providers have at least some training in its use at the bedside. Conceptually, the use of transtracheal US to confirm ETT placement relies on the differing anatomy of the trachea and esophagus. Recall that the trachea remains open due to cartilaginous rings while the esophagus will collapse unless filled (e.g., by an ETT). Thus, an esophagus with an ETT will be more readily visualized adjacent to the trachea than one without. 

The sonographic appearance of the trachea is characterized by a bright, hyperechoic curvilinear structure with posterior shadowing and reverberation artifact (Figure 1). If the trachea was intubated, then a single bullet sign [5] (Figure 2) will be visualized, which is an increase in both the echogenicity and the posterior artifact indicating the presence of an air-filled ETT. 

Figure 1: Sonographic view of trachea showing air-mucosa interface with posterior reverberation and shadowing artifact. [Photo courtesy of John Bailitz, MD]

Figure 2: Clip demonstrating the bullet sign: a single air-mucosa interface with increased posterior shadowing and artifact indicates the trachea has been intubated. [Photo courtesy of John Bailitz, MD]

Conversely, if the esophagus is intubated, then a double tract sign [6] (Figure 3) will be visualized, which is the appearance of a “second” trachea, or a similar hyperechoic line with posterior shadowing and reverberation artifact lateral to that of the trachea. This second air-mucosa interface indicates that the esophagus is stented open by an air-filled ETT.

Figure 3: Clip demonstrating the double tract sign: the appearance of a second air-mucosa interface with posterior artifact adjacent to the trachea indicates the esophagus has been intubated. [Photo courtesy of John Bailitz, MD]

How it is used

As alluded to above, the primary use of US in confirming ETT placement is determining that the trachea, rather than the esophagus, has been intubated. This can be confirmed either statically or dynamically. In static confirmation, the US probe is used post-intubation to visualize either the bullet sign or the double tract sign. Additionally, if the operator is uncertain, she or he could lightly move the ETT up and down to ascertain if there is movement in the region of the trachea or esophagus7. In dynamic confirmation, the US probe is used during intubation to visualize the increase in artifact as the tube passes into the trachea or the appearance of artifact as the tube passes into the esophagus.

Of note, transtracheal US cannot be used to determine the distance of the ETT from the carina or to determine if the right mainstem bronchus has been intubated. Thoracic ultrasound, however, can be used to observe bilateral pleural sliding but requires multiple ventilations. Additionally, anatomical variance may cause the esophagus to be positioned directly posterior to the trachea, leading to false positive tracheal intubations [8]. 

Technique [6–8]

1. Use a high frequency linear probe with sonographic gel applied liberally. 

2. Place the probe superior to the suprasternal notch in a transverse orientation, being careful to minimize downward pressure.

3. Adjust sonographic depth (depending on body habitus) to visualize the trachea and, if visible, the esophagus which will typically lie posterolateral to the trachea. 

4. Interpret:

   1. If performing static confirmation post-intubation, look for the bullet sign or the double tract sign.

   2. If performing dynamic confirmation during intubation, look for an increase in motion artifact posterior to the trachea or the appearance of a “second” trachea (double tract sign). 

Brief Review of Evidence

A meta-analysis pooled data from 11 studies and 969 intubations and showed an aggregate sensitivity of 98% and specificity of 94% in emergency intubations, with capnography as the gold standard [5]. More recently, a meta-analysis of 17 studies and 1,596 patients showed a sensitivity of 98.7% and specificity of 97.1%, with a positive likelihood ratio of 34.4 and a negative likelihood ratio of 0.019. This compares favorably to pooled data from studies examining capnography, which in one meta-analysis showed slightly lower sensitivity but similar specificity (93% and 97%, respectively)2,10. Furthermore, POCUS has several distinct advantages over capnography as mentioned above. 

POCUS is a skill familiar to many ED providers. A pilot study in a non-emergent, controlled operating room setting of patients intubated by anesthesiologists demonstrated that ED providers with no formal airway US training could identify tracheal intubations with a sensitivity and specificity approaching 100% [8]. In a cadaver study, the performance of residents compared favorably to that of ultrasound fellowship-trained emergency physicians, ranging from 91-100% sensitivity and 48-96% specificity depending on cadaver body habitus [11].

In the emergent setting, ultrasound assessment not only has high sensitivity and specificity for tracheal intubation but can be performed rapidly. A study of patients being intubated for impending respiratory failure, cardiac arrest, or trauma found that ED residents trained in airway US could identify tracheal intubation using ultrasound with 98.9% sensitivity, 94.1% specificity, and a 93% concordance with criterion standard quantitative capnography. Furthermore, confirmation of ETT tube with ultrasonography could be performed within an average of nine seconds [6].  During CPR, real-time tracheal ultrasonography was 100% sensitive and 85.7% specific for detecting tracheal versus esophageal intubation compared to the combined criterion standard of waveform capnography and auscultation. Furthermore, this study examined ultrasonography performed during chest compressions, suggesting that ultrasonography can be a highly reliable method of ETT confirmation without interrupting compressions [12]. 

Summary

• Established methods of confirming ETT placement in an emergent intubation are imperfect. 

• Quantitative waveform capnography has reduced sensitivity in the setting of a cardiac arrest or other low-flow states and requires multiple ventilations prior to confirmation. 

• Ultrasound can rapidly be used to confirm ETT placement with comparable sensitivity and specificity to criterion standards without requiring ventilation or an interruption of chest compressions.

• Providers with some familiarity with US can use it to distinguish between tracheal and esophageal intubations reliably.

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Expert Commentary

Thank you for his outstanding review of an exciting and relatively new application in Emergency Ultrasound. Although the literature on this topic has exploded in the last few years, tracheal ultrasound was already included in the 2015 ACLS Guidelines as a reliable method to confirm endotracheal intubation. 

As a longtime ultrasonographer and resuscitationist, I find this application particularly useful in two common ED situations. The first is out of hospital cardiopulmonary arrest in which the patient was already intubated by paramedics in the field. As the patient arrives in the resuscitation bay, there are a number of competing priorities. Rapid confirmation of correct endotracheal tube placement during chest compressions allows the team to quickly move on to other priorities. The second is the difficult intubation of the crashing ED patient. Particularly, in patients who are obese or otherwise have distorted airway anatomy, the ultrasound machine provides real time visualization of the endotracheal tube placement, or a rapid confirmation immediately after. In either situation, the ultrasound machine will certainly be helpful not only for confirmation of ETT location, but further for ruling out pneumothorax and main stem intubation, before moving onto other causes of cardiac arrest such as cardiac tamponade, massive PE, and blood loss. 

Regarding technique, dynamic visualization during intubation may be difficult particularly if external laryngeal manipulation while is being preformed. So static visualization immediately after placement is often more feasible. Forceful, or up and down movement of the tube may dislodge an endotracheal tube, damage the airway, or stimulate a cough or vomiting in the non-paralyzed patient. Instead, simply gently rotating the tube from side to side creates an easily visible change in the tracheal air column if correctly located, or “esophageal sliding” of the mucosa over the endotracheal tube if incorrectly placed in the esophagus.

Final shout outs to the authors of this well written blog. But also to Dr. Michael Gottlieb, full disclosure my former fellow, for his considerable research in this area. Dr. Gottlieb first identified the need for better confirmatory methods as an EM intern. Although I was initially skeptical as a resuscitationist, Dr. Gottlieb quickly convinced me with a well-done literature review during which he identified a gap in the existing literature. Dr. Gottlieb then took the initiative and turned one research question into an exciting are of scholarship for his career and the many fellows that followed that benefitted from Dr. Gottlieb’s mentoring. This is such a wonderful example of turning a simple clinical question into a rich and rewarding area of leadership through scholarship!

John Bailitz, MD

Vice Chair for Academics

Department of Emergency Medicine

Northwestern Feinberg School of Medicine

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Citations

1. MacLeod BA, Heller MB, Gerard J, Yealy DM, Menegazzi JJ. Verification of endotracheal tube placement with colorimetric end-tidal CO2 detection. Ann Emerg Med [Internet] 1991 [cited 2019 Jan 8];20(3):267–70. Available from: http://www.ncbi.nlm.nih.gov/pubmed/1899985

2. Li J. Capnography alone is imperfect for endotracheal tube placement confirmation during emergency intubation. J Emerg Med [Internet] 2001 [cited 2019 Jan 8];20(3):223–9. Available from: http://www.ncbi.nlm.nih.gov/pubmed/11267809

3. Takeda T, Tanigawa K, Tanaka H, Hayashi Y, Goto E, Tanaka K. The assessment of three methods to verify tracheal tube placement in the emergency setting. Resuscitation [Internet] 2003 [cited 2019 Jan 8];56(2):153–7. Available from: https://www.sciencedirect.com/science/article/pii/S0300957202003453

4. DeIorio NM. Continuous end-tidal carbon dioxide monitoring for confirmation of endotracheal tube placement is neither widely available nor consistently applied by emergency physicians. Emerg Med J [Internet] 2005 [cited 2019 Jan 13];22(7):490–3. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15983084

5. Das SK, Choupoo NS, Haldar R, Lahkar A. Transtracheal ultrasound for verification of endotracheal tube placement: a systematic review and meta-analysis. Can J Anesth Can d’anesthésie [Internet] 2015 [cited 2019 Jan 11];62(4):413–23. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25537734

6. Chou H-C, Tseng W-P, Wang C-H, et al. Tracheal rapid ultrasound exam (T.R.U.E.) for confirming endotracheal tube placement during emergency intubation. Resuscitation [Internet] 2011 [cited 2019 Jan 9];82(10):1279–84. Available from: http://www.ncbi.nlm.nih.gov/pubmed/21684668

7. Chao A, Gharahbaghian L. Tips and Tricks: Airway Ultrasound [Internet]. Am. Coll. Emerg. Physicians Emerg. Ultrasound Sect. 2015 [cited 2019 Jan 13];Available from: https://www.acep.org/how-we-serve/sections/emergency-ultrasound/news/june-2015/tips-and-tricks-airway-ultrasound/#sm.00000hnz0e2u2ofnizwz7io2f5wg6

8. Werner SL, Smith CE, Goldstein JR, Jones RA, Cydulka RK. Pilot study to evaluate the accuracy of ultrasonography in confirming endotracheal tube placement. Ann Emerg Med [Internet] 2007 [cited 2019 Jan 9];49(1):75–80. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17014927

9. Gottlieb M, Holladay D, Peksa GD. Ultrasonography for the Confirmation of Endotracheal Tube Intubation: A Systematic Review and Meta-Analysis. Ann Emerg Med [Internet] 2018 [cited 2019 Jan 16];72(6):627–36. Available from: http://www.ncbi.nlm.nih.gov/pubmed/30119943

10. Gottlieb M, Bailitz J. Can Transtracheal Ultrasonography Be Used to Verify Endotracheal Tube Placement? Ann Emerg Med [Internet] 2015 [cited 2019 Jan 11];66(4):394–5. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25805115

11. Gottlieb M, Bailitz JM, Christian E, et al. Accuracy of a novel ultrasound technique for confirmation of endotracheal intubation by expert and novice emergency physicians. West J Emerg Med [Internet] 2014 [cited 2019 Jan 13];15(7):834–9. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25493129

12. Chou H-C, Chong K-M, Sim S-S, et al. Real-time tracheal ultrasonography for confirmation of endotracheal tube placement during cardiopulmonary resuscitation. Resuscitation [Internet] 2013 [cited 2019 Jan 10];84(12):1708–12. Available from: http://www.ncbi.nlm.nih.gov/pubmed/23851048

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How To Cite This Post

[Peer-Reviewed, Web Publication] Hajjar M, Ireland A. (2019, Nov 4). Ultrasound Confirmation of ETT Placement. [NUEM Blog. Expert Commentary by Bailitz J]. Retrieved from http://www.nuemblog.com/blog/us-ett.

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