Research ArticleSpecial Article (PRO/CON)

Portable Handheld Point-of-Care Ultrasound for Detecting Unrecognized Esophageal Intubations

Gabrielle A White-Dzuro, Lauren E Gibson, Lorenzo Berra, Edward A Bittner and Marvin G Chang
Respiratory Care May 2022, 67 (5) 607-612; DOI: https://doi.org/10.4187/respcare.09239

Abstract

Esophageal intubations are not an uncommon occurrence in prehospital settings, occurring as high as 17%. These “never events” are associated with significant morbidity and mortality especially when unrecognized or when there is delayed recognition. Here, we review the currently available techniques for confirming endotracheal tube intubation and their limitations, and present the case for the application of portable handheld point-of-care ultrasound as an emerging technology for detection of potentially unrecognized esophageal intubations such as during cardiac arrest. We also provide algorithms for confirmation of tracheal intubation.

Introduction

Esophageal intubations in the prehospital setting are not uncommon, occurring at a rate between 6%–17% in studies from Florida, Maine, Indiana, and New York.1-4 These “never-events” in health care are often not immediately recognized and are associated with a mortality rate as high as 90% in these studies. Incorrect endotracheal placement continues to occur despite the widespread use of confirmatory indicators, including colorimetric end-tidal CO2, self-inflating esophageal detector devices, lung auscultation, and observation of symmetric chest rise. In one study, clinicians failed to detect 25% of esophageal intubations despite the use of end-tidal CO2 or an esophageal detector device.

Multiple studies have confirmed the difficulty of placing endotracheal tubes (ETTs) in high pressure, hostile environments.5,6 In a retrospective study assessing out-of-hospital endotracheal intubation (ETI) by emergency medicine physicians, 3% of subjects had unrecognized esophageal intubations; and of these, 60% died due to prolonged hypoxia. The current standard of care for verifying ETI is the visualization of the ETT passing through the vocal cords, followed by the use of at least one additional technique for confirmation. Unfortunately, there are many situations in which visualization of the ETT passing through the vocal cords can be difficult, such as in patients with an anterior larynx or the presence of laryngeal edema or other causes of airway obstruction. It is also possible that the ETT can become dislodged after placement, particularly during patient repositioning or transport. Furthermore, a mistaken belief that a provider visualizes the ETT passing through the vocal cords can cause an anchoring with adverse consequences in the absence of other confirmatory information.

Here, we review the currently available techniques for confirming ETI and present the case for the application of portable handheld point-of-care ultrasound (POCUS) for the detection of potentially unrecognized esophageal intubation. Finally, we propose 2 algorithms to implement POCUS for confirming tracheal intubation.

Current Techniques to Confirm ETI

There are inherent limitations to each technique used to confirm ETI. Capnometry is an assessment of end-tidal CO2 levels through qualitative colorimetric assessment, whereas capnography provides a continuous display of the exhaled CO2. In a patient with a perfusing cardiac rhythm, the accepted standard for confirmation is end-tidal CO2 detection through continuous waveform capnography.7,8 However, there are still multiple situations in which capnography or capnometry may be unreliable, such as in cardiac arrest, where a patient does not have a perfusing rhythm. Capnometry may also provide false reassurance due to the detection of CO2 from the stomach or esophagus rather than from the lungs, which might occur if the patient recently ingested a carbonated beverage or received bystander ventilation.9,10 Quantitative waveform capnography is often not available in out-of-hospital settings, and studies have found that it has only 60–68% sensitivity at confirming ETI during cardiac arrest.11-13

Compared to capnometry and capnography, auscultation has a lower sensitivity (94%) and specificity (66–90%) for confirming ETI.7,14,15 For this reason, auscultation alone is not considered a sufficiently reliable method to confirm ETT placement. High levels of ambient noise can make auscultation particularly difficult, if not impossible, in many prehospital settings. Auscultation with ventilation after esophageal intubation results in insufflation of the stomach, increasing aspiration risk on subsequent intubation attempts, and, at worst, could be mistaken as breath sounds.

Videolaryngoscopy is often a preferred method because not only does it allow direct visualization of the ETT through the vocal cords it also increases first-attempt success with intubation, especially in high-acuity situations and in patients with difficult airways. Among non-experts, videolaryngoscopy leads to higher rates of intubation success on first attempt, decreases time to achieve intubation, and reduces the incidence of esophageal intubation.16,17 However, videolaryngoscopy is more expensive than conventional direct laryngoscopy and can be challenging to use in situations where the camera is obscured by secretions or blood in the airway. Whereas videolaryngoscopy significantly reduces esophageal intubation, it does not completely prevent them as seen in a study by Mosier et al18 where the rate of esophageal intubation was reduced from 12.5% with direct laryngoscopy to 1.3% with videolaryngoscopy. Despite direct visualization of the ETT during intubation, it is possible for an ETT to migrate out during chest compressions or securing of the ETT.

Fiberoptic bronchoscopy can also be used to quickly confirm successful ETI assuming the bronchoscope is readily available and pre-setup for use.19 However, often fiberoptic scopes are not readily available depending on the setting; and when needed emergently, they take time to deploy given their often large footprint and the setup time could prolong total time required to confirm ETI especially in emergencies such as cardiac arrest. Furthermore, fiberoptic scopes are expensive and may need to be decontaminated between usage, which may limit their availability and use for ETI confirmation. The use of fiberoptic bronchoscopy for ETI confirmation is also dependent on having access to reliable suction, and visualization is often limited when there is significant airway bleeding.

It is important to note that provider experience is an important factor in determining the likelihood of success with ETI.20,21 Wang et al22 found improved patient survival when emergency medical services (EMS) providers with more intubation experience performed intubation. The odds ratio was 1.5 for survival if intubated by rescuers with > 50 previous intubations as compared to those with < 10 intubations.

The Role of Point-of-Care Ultrasound (POCUS)

There have been several systematic reviews verifying the accuracy of POCUS in determining ETT placement.23-26 We have also recently published a review on the use of handheld POCUS in emergency airway management.27 Multiple ultrasonographic techniques can confirm tracheal intubation. Lung ultrasound can be used to visualize the parietal and visceral pleura sliding against each other, often referred to as lung sliding. For this technique, a linear probe is placed longitudinally on the anterior chest wall in the midclavicular line at the level of the third to fifth rib interspaces, first on one side and then the other. The pleura can be visualized as a bright line between the rib shadows. With inhalation or delivery of a positive-pressure breath, the pleura slides in the view (Supplemental Video 1, see related supplementary materials at http://www.rc.rcjournal.com). In the case of esophageal intubation or other obstructions to positive-pressure ventilation, there will be no pleural motion (Supplemental Video 2, see related supplementary materials at http://www.rc.rcjournal.com). Motion-mode (M-mode) tracks the movement of the pleura over time. On this assessment, a speckled appearance (described as a “sandy beach”) represents pleural motion (Fig. 1A), implying appropriate lung ventilation. In contrast, a linear appearance (similar to a “bar code”) represents no motion of the pleura (Fig. 1B) that may suggest esophageal intubation (absent lung sliding bilaterally) or mainstem intubation (absent lung sliding unilaterally). Studies have shown bilateral lung sliding to have a sensitivity and specificity of 92–100% and 100% and positive and negative predictive values of 100%, respectively, for successful tracheal intubation.25,28,29 The use of M-mode aids in the diagnosis of lung sliding and shortens the learning curve associated with its assessment.30 It is important to note that the absence of lung sliding is also seen in other conditions such as pneumothorax, mucous plugging, pneumonia, severe COPD, and pulmonary fibrosis.

Fig. 1.
Fig. 1.

M-mode of lung ultrasound allows for assessment for lung sliding. Panel A shows a “sandy beach” appearance consistent with pleural movement. Panel B shows a “bar code” appearance consistent with a lack of pleural motion.

Transtracheal ultrasonic assessment is another technique to confirm ETI. With this technique, the ultrasound probe is placed transversely at the level of the suprasternal notch. ETI is confirmed by visualization of a collapsed esophagus adjacent to the trachea (Fig. 2A) or by the absence of the “double tract” sign, which is the presence of 2 air-mucosae interfaces suggestive of esophageal intubation (Fig. 2B). In both pediatric and adult populations, the transtracheal ultrasound technique alone has a sensitivity of 92–100%, a specificity of 97–100%, and positive and negative predictive values of 100% and 71–100%, respectively, for successful tracheal intubation.23-25,31 With the combination of lung sliding and transtracheal assessment in a single evaluation, the sensitivity and specificity are 100% and 80–100% and positive and negative predictive values of 99–100% and 100% for confirming successful tracheal intubation.28,32,33

Fig. 2.
Fig. 2.

Transtracheal ultrasound allows for the determination of tracheal or esophageal intubation. Panel A shows a collapsed esophagus adjacent to the trachea, consistent with tracheal ventilation. Panel B shows the “double tract” sign, which is the presence of 2 air-mucosae interfaces, consistent with esophageal intubation.

Whereas determining esophageal intubation is critical for preventing unnecessary mortality, preventing mainstem intubation is essential for ensuring adequate ventilation and protecting against barotrauma. Studies have shown that 10–15% of patients intubated in the prehospital setting arrives at the hospital with a mainstem intubation.4,34 Use of ultrasound with the determination of bilateral lung sliding is a more accurate method for excluding the presence of mainstem intubation compared to auscultation. Ramsingh et al35 compared lung auscultation to ultrasound assessment by blinded anesthesiologists randomized to subjects with tracheal, right mainstem, and left mainstem intubations in the operating room. They found auscultation to have a sensitivity and specificity of only 66% and 59% for detection of mainstem intubation, whereas ultrasound assessment had a sensitivity and specificity of 93% and 96%, respectively, for successful tracheal intubation.

Accessibility of Lung Ultrasound

An important aspect of the utility of a new technology is its accessibility, including its cost, ease of use, and associated learning curve. The introduction of new portable, handheld devices is making ultrasound an increasingly accessible technology.36,37 These devices are relatively inexpensive compared to traditional ultrasound machines, ranging in price from $2,000–$12,500, and are quite small, allowing them to be stored in an ambulance or carried in the pocket of an EMS provider; ideal for use in the prehospital setting. Available devices conveniently connect to smartphones or tablets and can quickly transfer information to providers at an accepting hospital over a cellular network. These portable ultrasound devices allow for integration with picture archiving and communication systems and the sharing of images for learning and consultation purposes. Some devices have also incorporated teleguidance technology, which could enable first responders to receive guidance from remote expert providers through live-image acquisition and feedback.

Multiple recent studies have shown that practitioners can quickly become proficient in POCUS.38-42 Mason and colleagues39 examined pre- and post-test performance after three 1-h training sessions for flight nurses with no prior ultrasound experience. They saw a statistically significant improvement in their ultrasound interpretation skills during the brief training period. A study of emergency medicine residents and attending physicians showed that after a brief tutorial and 2 practice attempts they were able to interpret ultrasound for intubation with near-perfect sensitivity and specificity and at an average speed of 4 s.38 Another study showed that after a brief presentation first responders were able to correctly identify lung sliding with a sensitivity and specificity of 0.95 and 1.00.

Tracheal POCUS to confirm ETI can be performed quickly and with minimal training.16,43,44 Chowdhury et al found that anesthesia trainees were faster at identifying the location of the ETT with ultrasound than with auscultation or capnography.45 Pfeiffer et al43 similarly found that when compared with lung auscultation and capnography lung ultrasound was just as fast as auscultation alone and faster than the standard method of combined auscultation and capnography. Outside the scope of this article, ultrasound may also play a role in identifying the cricothyroid membrane to perform a cricothyrotomy in case of failed intubation and difficult ventilation, especially in settings where patients are suspected of being a difficult intubation, which ultrasound also has a role in assessing.27,46

Point-of-Care Ultrasound Algorithm

We propose 2 standardized ultrasound algorithms to confirm proper ETI for use by prehospital EMS crews. The standardized algorithms are designed to assist providers in quickly identifying the location of an ETT and in correcting the situation if there is an esophageal or mainstem intubation. Both algorithms recommend that intubation be performed by an experienced member of the EMS crew using videolaryngoscopy. The use of videolaryngoscopy allows other members of the team to visualize the passage of the ETT through the vocal cords and provides a recording of the intubation for medicolegal purposes. Before securing the ETT, POCUS should be used with other standard techniques to confirm its location. Standardized algorithms will help providers interpret their findings and quickly correct them in the setting of esophageal intubation. The first proposed algorithm is designed to be used when there are fewer than 3 members of the airway team (Fig. 3), whereas the second proposed algorithm is intended for scenarios when 3 or more providers are present (Fig. 4). In this secondary scenario, one provider performs intubation, one provides intubation assistance, and the third focuses solely on point-of-care transtracheal ultrasound. Tracheal ultrasound does allow for real-time assessment of ETT location before ventilation, but it can be distracting if it’s not the sole focus of a single provider to perform ultrasound during the intubation as we have found from experience as part of our institution’s airway response team. When intubation is done as a 2-person team, the provider who is assisting in intubation is often helping to administer anesthetic drugs, manage hemodynamics, and provide laryngeal manipulation, which makes it challenging for the same person to perform tracheal ultrasound to assess the real-time ETT location. In settings such as the ICU where there are nurses and respiratory therapists who can be delegated these tasks, it may be possible to perform our second proposed algorithm when there are fewer than 3 providers as was likely the case in the prospective, multi-center, observational study by Mourad et al47 where the same algorithm was used to confirm ETI, detect mainstem intubations, and adjust tube positioning in the critically ill with a high degree of accuracy.

Fig. 3.
Fig. 3.

This algorithm can guide prehospital EMS crews through point-of-care ultrasound to assess for tracheal or esophageal intubation. This algorithm is preferred if only one or 2 providers are part of the airway team. ETT = endotracheal tube.

Fig. 4.
Fig. 4.

This algorithm can guide prehospital EMS crews through point-of-care ultrasound to assess for tracheal or esophageal intubation. This algorithm is preferred if only 3 or more providers are part of the airway team, and one provider is dedicated solely to point-of-care ultrasound (POCUS). ETT = endotracheal intubation.

Both of our proposed algorithms converge on the assessment of bilateral lung sliding to both confirm correct ETT placement as well as adequate ventilation. We acknowledge that whereas lung sliding requires ventilation and, therefore, puts the patient at risk of insufflation with an incorrectly placed ETT, this is not uncommon for other confirmatory techniques such as end-tidal CO2 detection. If lung sliding is absent bilaterally, the ETT should be removed immediately as the risks of esophageal intubation outweigh the benefits of remaining intubated. With unilateral lung sliding, mainstem intubation should be the first consideration, and the depth of the ETT should be assessed. Other etiologies of unilateral lung sliding include a pneumothorax, mucous plugging, airway obstruction, or severe COPD.

Summary

Esophageal intubation is a common complication of ETI associated with morbidity and mortality. Limitations in the availability and accuracy of existing techniques for confirmation of ETT position contribute to the occurrence of the complication. POCUS has been demonstrated to easily and accurately identify the ETT position during intubation. We suggest the utilization of lung and transtracheal POCUS in conjunction with other assessment techniques for confirmation of the appropriate ETT position especially during scenarios where confirmation with end-tidal CO2 may not be reliable such as cardiac arrest. The proposed algorithms can serve as a means to integrate portable handheld POCUS into the existing practice of prehospital providers to detect esophageal intubations. With these measures, we hope to reduce the incidence of unrecognized esophageal intubation and truly turn these into “never-events.”

Acknowledgments

We thank Dr Michael Gottlieb for the use of his image of tracheal ultrasound (Fig. 2).

Footnotes

  • Correspondence: Marvin G Chang MD PhD, Harvard Medical School, Division of Cardiac Anesthesia and Critical Care, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, 55 Fruit Street GRB 444, Boston, Massachusetts, 02114. E-mail: mgchang{at}mgh.harvard.edu

  • The authors have disclosed no conflicts of interest.

  • Supplementary material related to this paper is available at http://rc.rcjournal.com.

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