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Table of Contents
Year : 2018  |  Volume : 7  |  Issue : 4  |  Page : 192-196

Three-window ultrasonography confirmation of endotracheal tube placement

1 Department of Emergency Medicine, University of California, Irvine, California, USA
2 Department of Pulmonary and Critical Care, University of California, Irvine, California, USA
3 Stritch School of Medicine, Loyola University Chicago, Illinois, USA

Date of Web Publication31-Dec-2018

Correspondence Address:
Dr. Shadi Lahham
333 City Boulevard West, Suite 640, Route 128-01, Orange, California
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/rcm.rcm_24_18

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Background: Establishing a definitive airway is often an initial step in the management of critically ill patients in the emergency department (ED). Currently, there is no universally accepted gold standard for airway confirmation. Recent literature has shown that point-of-care ultrasound (POCUS) may be helpful in confirming the correct endotracheal tube (ETT) placement. Objective: The objective of this study is to evaluate the accuracy of a comprehensive three-window POCUS assessment to confirm correct ETT placement. Methods: This was a prospective, single-center, observational study using a convenience sample of patients in the ED and Medical Intensive Care Unit. After presumed successful ETT intubation, three sonographic windows were obtained, which included the trachea, bilateral lung sliding, and diaphragm movement. Results: We enrolled a total of 140 patients. There were no esophageal intubations. The three-window POCUS method correctly identified 132 of 137 ETTs placed in the trachea with 96.4% sensitivity (95% confidence interval [CI] 91.7%–98.8%) and 33.3% specificity (95% CI 0.8%–90.6%). Only one of the three mainstem intubations was identified using POCUS. Ultrasound assessment was completed on average 25 min quicker than the usual confirmatory plain film radiography (95% CI 6.2–43.9 min, P = 0.005). Conclusions: The three-window POCUS assessment is a rapid and potentially reliable method to identify ETT intubation, but may not be reliable at confirming mainstem intubation.

Keywords: Critical care ultrasound, emergency ultrasound, intubation, pulmonary ultrasound, ultrasound

How to cite this article:
Lahham S, Wilson SP, Turner E, Subeh M, Rosen MA, Youssefian A, Anderson CL, Hosseini M, Rosen S, Gari A, Fox JC. Three-window ultrasonography confirmation of endotracheal tube placement. Res Cardiovasc Med 2018;7:192-6

How to cite this URL:
Lahham S, Wilson SP, Turner E, Subeh M, Rosen MA, Youssefian A, Anderson CL, Hosseini M, Rosen S, Gari A, Fox JC. Three-window ultrasonography confirmation of endotracheal tube placement. Res Cardiovasc Med [serial online] 2018 [cited 2021 Apr 22];7:192-6. Available from: https://www.rcvmonline.com/text.asp?2018/7/4/192/249048

  Introduction Top

Establishing a definitive airway is often an initial step in the management of critically ill patients. In the emergency setting, this can be particularly challenging. Depending on the experience of the intubating physician, up to a quarter of emergent intubations are incorrectly placed in the esophagus.[1],[2],[3],[4] Undetected esophageal intubation can result in significant morbidity and mortality. Even when an endotracheal tube (ETT) is correctly placed in the trachea, there is a risk of passing the tube too deep, resulting in a right or left mainstem bronchus intubation. These mainstem bronchus intubations can result in hypoventilation or pneumothorax and are believed to occur in up to a quarter of emergent ETT intubations.[5],[6],[7]

Standard methods for confirming proper ETT position include visualizing ETT passing through vocal cords, assessing for bilateral chest rise, auscultating bilateral lung fields, continuous pulse-oximetry measurements, identifying end-tidal CO2 through colorimetric or continuous measurements, and plain film radiography to confirm depth. While the American Heart Association recommends the use of capnography to confirm placement, there is no universally accepted gold standard as all these methods have limitations and are therefore usually performed in some combination based on physician preference.[8],[9]

Recently, several studies have demonstrated that point-of-care ultrasound (POCUS) may be both sensitive and specific for correct ETT placement. The single-window approach with the lung sliding sign has been demonstrated to be a potentially reliable method for determining appropriate ETT placement during both elective and emergent intubation.[10],[11],[12] Another single-view technique, visualization of the anterior trachea, has been demonstrated to be a potential reliable method to confirm nonesophageal intubation, but cannot identify mainstem intubations.[13] A novel study by Park et al. also had favorable results using both transtracheal visualization along with lung sliding to confirm ETT placement.[14] A third single-window approach, which evaluates for diaphragmatic motion has also shown promise in identifying correct ETT position.[15] However, to date, there have been no studies evaluating the use of a comprehensive three-window approach to assess the lungs, trachea, and diaphragm together to confirm correct ETT placement.


We sought to evaluate the accuracy of a comprehensive three-window POCUS assessment to confirm the placement of ETT in the trachea or mainstem bronchus when compared to the usual postintubation clinical assessment. We then sought to compare the accuracy and time-intervals of a comprehensive three-window POCUS assessment to appropriately identify the correct ETT trachea only placement (nonmainstem bronchus intubation) to a postintubation plain film radiograph.

  Methods Top

Study design

This study was a prospective, observational study using a convenience sample of patients that underwent emergent intubation in the Emergency Department (ED) or Medical Intensive Care Unit (MICU). The study site institutional review board approved this study.

Study setting and population

This study was performed at an academic 350-bed level 1 Trauma Center between July 2011 and August 2013, with an annual ED patient census of 50,000 visits. Any patient requiring emergent intubation as a result of cardiac, respiratory, or impending neurologic failure while a research assistant was available was eligible for enrollment in the study. Research assistants were available between the hours of 8:00 am and midnight, 7 days per week. Patients were excluded if they were <18 years of age, pregnant, or undergoing elective or fiber optic intubation.

Study protocol

All physicians involved in data collection were required to review an instructional presentation and receive a brief hands-on bedside training session by one of the study coinvestigators before participating in the study. This training session required physicians to identify all relevant anatomical landmarks on live, healthy models using ultrasound to qualify for participation. Thirty-three physicians qualified for the study and thirty-on participated by enrolling at least one patient into the study using the three-window POCUS assessment. Physician experience varied between 1st year resident and fellowship trained attending physicians. Sonosite M-Turbo and Edge ultrasound machines (FUJIFILM, Seattle WA) equipped with linear array (10-5 MHz) and phased array (5-2 MHz) transducers were used to obtain all ultrasonographic images.

Emergent intubations were performed by direct or video-assisted laryngoscopy at the discretion of the physician performing intubation. Immediately, after presumed successful intubation (determined by combination of visualization of ETT passing through vocal cords, assessment of chest rise, lung auscultation, pulse-oximetry, and end-tidal CO2 measurements at the discretion of the intubating or supervising physician), a plain film radiograph of the chest was ordered in accordance with the current standard of care. Following intubation, a research assistant brought the ultrasound machine to bedside for evaluation while X-ray technician was contacted for postprocedural imaging. Next, either the intubating or supervising physician performed the three-window POCUS examination, while the patient was undergoing manual ventilation and reported their immediate interpretation before reviewing the plain film chest radiograph. There was no provision to blind the physician performing the sonographic evaluation from the result of the intubation; in some instances they were the same person.

Ultrasound protocol

The first ultrasound window obtained was visualization of the ETT within the trachea [Figure 1]. For visualization of this window, a linear array transducer was placed in a transverse plane midline and superior to the suprasternal notch. After intubation, we verified proper ETT placement by visualizing a hyperechoic and curved structure in the trachea that produced “comet tails” and hypoechoic artifacts projecting posteriorly. Visualization of a second airway or hypoechoic shadows within the esophagus was considered an esophageal intubation.
Figure 1: Illustration of transverse ultrasound view of the anterior neck. Trachea is located in the middle of the image with distal shadow due to air

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The second ultrasound (US) window evaluated for bilateral lung sliding as evidence of adequate ventilation of both lungs [Figure 2] and [Figure 3]. For this window, the linear array transducer was placed vertically with the orientation marker cephalad, in the midclavicular line, perpendicular to the ribs, in the second or third intercostal space of the chest bilaterally. With this view, ventilation was confirmed with the visualization of sliding between the parietal and visceral pleura. The ETT was suspected of being inserted too deeply into the contralateral mainstem bronchus if sliding appeared to be decreased or absent compared to the contralateral side. Similarly, the presence of bilateral, symmetric lung sliding indicated proper placement of the ETT within the trachea resulting in equal ventilation of both lungs.
Figure 2: Illustration of M-mode showing the anterior chest wall with lung sliding

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Figure 3: Illustration of M-mode showing the anterior chest wall with lack of lung sliding

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The third US window aimed to identify bilateral downward diaphragmatic excursion during lung insufflation [Figure 4]. The phased array transducer was placed over the lower chest from seventh to ninth intercostal spaces bilaterally in the mid-axillary line to detect diaphragmatic motion. We assumed that if the diaphragmatic excursion was decreased unilaterally, then the ETT was inserted into the contralateral mainstem bronchus and therefore, not ventilating the ipsilateral lung. Conversely, we assumed that if the ETT was in the correct position, ventilation of both lungs should produce bilateral, symmetric diaphragmatic movement.
Figure 4: Ultrasound illustration of the visualization of the diaphragm (arrow)

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Outcome measures

Prior to reviewing the chest X-ray, physicians reported to the research assistant their interpreted location of the ETT to be in the trachea, esophagus, right mainstem bronchus, left mainstem bronchus, or unknown. We recorded time to three-window POCUS completion, time to plain film radiography completion, and time to official plain film radiography interpretation of ETT placement (trachea, left or right mainstem bronchus) by radiology. A true positive was defined as an ETT intubation (not mainstem intubation) confirmed on plain film radiography, as diagnosed using POCUS. A true negative was defined as and esophageal intubation, confirmed with ultrasound.

Data analysis

We collected and managed study data using Research Electronic Data Capture electronic data capture tools (Harris). We analyzed the data using Stata (Version 12.1, StataCorp, College Station, TX, USA). We calculated test characteristics for ultrasound interpretations using CO2 capnography as the gold standard for tracheal intubation and plain radiology radiograph interpretation to confirm that there was no mainstem intubation. Mean time to ultrasound and plain film radiograph completion are reported. We used a one-sample t-test to compare the mean time of ultrasound and plain film radiograph completion.

  Results Top

Characteristics of subjects

We enrolled a total of 140 patients, of which 61 (43.6%) were intubated in the ED and 79 (56.4%) in the MICU. The majority of study participants were male (57.9%) with median age being 59 years old, and median body mass index was 26.7 [Table 1].
Table 1: Basic patient demographics, known medical history and location of intubation

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Main results

The three-window POCUS method correctly identified the ETT to be either in the trachea or mainstem bronchus (nonesophageal) in all 140 instances, sensitivity of 100.0% (95% confidence interval [CI] 97.4%–100.0%) when compared to the postintubation clinical assessment as previously described. No esophageal intubations were identified using POCUS.

Secondary results

The three-window POCUS method correctly identified 132 of 137 ETTs placed in the trachea. Of the remaining three patients with mainstem intubation, only one was identified with POCUS. Sensitivity and specificity for correct ETT in the trachea only by three-window POCUS was 96.4% (95% CI 91.7%–98.8%) and 33% (95% CI 0.84%–90.6%), respectively. The mean time between intubation and three-window POCUS completion was 27.8 min (95% CI 21–34 min). Positive predictive and negative predictive values were 98.5% (95% CI 96.7%–99.3%) and 16.7% (95% CI 3.2%–55.2%), respectively. The mean time between intubation and plain film radiography completion was 52.8 min (95% CI 36–70 min). Mean time between intubation and official radiology interpretation was 474 min (95% CI 370–522 min). Three-window POCUS was completed on average 25 min faster than plain film radiography (95% CI 6.2–43.9 min, P = 0.005).

  Discussion Top

In critically ill patients, establishing an airway is often the first step in resuscitation. Thus, when indicated, it is imperative to establish a definitive airway as quickly and safely as possible. Although there are different tools and techniques to confirm correct placement of an ETT, there is no agreed on gold standard as each method has its limitations. Typically, in emergent airways, a combination of direct laryngoscopy, end-tidal CO2, and auscultation are used to confirm placement. In the present study, our data suggest that in situ ations requiring emergent intubation, the three-window POCUS assessment may be both an efficient and accurate method for the early and correct placement of the ETT in the trachea when used as an adjunct to the clinical assessment, but may not be accurate at identifying a mainstem intubation. We stress the importance of the clinical assessment, as the intubating clinician generally utilizes a combination of all the tools available in rapid succession to determine if another intubation attempt is needed. For this reason, our primary aim compared the accuracy of detecting a nonesophageal intubation to the clinical assessment, given that clinicians would reattempt intubation before using ultrasound or chest radiography. Attempting to blind the sonologist with a presumed esophageal intubation could lead to the disastrous consequences of an esophageal intubation.

Interestingly, in the evaluation of three-window POCUS against plain film radiography to confirm trachea versus mainstem bronchus intubation, we observed an adequate sensitivity to allow for the potential temporary delay of confirmatory plain film radiography in instances where further clinical care supersedes the additional confirmation of plain film radiography or there is a delay to obtaining conventional radiographs. Such an instance would be in the unstable patient who needs central venous access or other invasive lines for hemodynamic monitoring. This delay in confirmation is also supported by the prior studies on ultrasound confirmation of ETT,[10],[13],[16],[17],[18],[19],[20],[21] as well as the meta-analysis by Das et al. but is not meant to replace standard of care or deviation from hospital policy.[22]

The most concerning finding in our study was that we observed two mainstem bronchus intubations that were missed by the POCUS assessment, yet were detected by plain film radiography. Both of these were found to be 1–2 cm past the carina. We believe that in these two cases, since the ETT was minimally distal to the carina, air was able to pass into the contralateral lung through the side port and provided enough ventilation to the contralateral lung to create a detectable lung sliding and diaphragmatic excursion by sonographic assessment. We suspect that if the ETT had been advanced slightly further, the opposite lung would have not been ventilated and thereby likely been more evident on US. It is because of these two missed mainstem bronchus intubations that we also cannot advocate discontinuing use of the plain film radiography in confirmation of ETT placement, but still believe there may be a role for the early detection and adjustment of the majority of improperly placed tubes. In addition, our study population did not have any esophageal intubations thus we are not able to draw conclusions on esophageal intubations based on our data.


There were several limitations to our study. First, it was performed at a single center with a robust hospital-wide POCUS program, which may not be the case at other institutions. Therefore, it is possible that our physician sonographers (sonologists) may be more skilled at image acquisition and interpretation than physicians at other sites. Second, our sonologists were not blinded to the result of the intubation and would be able to interpret the patient's clinical condition such as continuous pulse oximetry and capnography. These findings alone would suggest probable appropriate ETT placement. Furthermore, though not part of our data collection, in some cases, the physicians performing the intubation had also performed the sonographic evaluation, which further confounds the issue of blinding. If the physician visualized the ETT passing through the cords during intubation, they would have a higher confidence of the ETT being in the correct location. In addition in our data, no esophageal intubations were identified using POCUS, thus, we cannot definitively state any conclusions on the ability of POCUS to identify esophageal intubation based on our data set. Finally, the small sample size does not allow adequate power to make a true noninferiority comparison.

  Conclusions Top

In our study, the three-window POCUS appears to be a reliable adjunct for the early confirmation of correct ETT placement in the trachea. Our data indicates that this method is not reliable for identifying mainstem bronchi intubations. With future advances in ultrasound technology and training, there may be a role for this technique to confirm placement while awaiting plain film radiography or even reduce the need for postintubation plain film radiography. Additional large-scale studies with greater number of esophageal and mainstem intubations are required to validate this conclusion.


The authors would like to acknowledge UCI Department of Emergency Medicine, UCI Pulmonary and Critical Care department, Emergency Medicine Research Associates Program, MICU Research Associates Program

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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[PUBMED]  [Full text]  
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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