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 Table of Contents  
Year : 2020  |  Volume : 7  |  Issue : 4  |  Page : 179-185

Utility of upper airway ultrasound for confirmation of endotracheal tube placement in the pediatric intensive care unit setting

Department of Pediatrics, Bharati Vidyapeeth Medical College and Hospital, Pune, Maharashtra, India

Date of Submission22-Mar-2020
Date of Decision10-May-2020
Date of Acceptance18-May-2020
Date of Web Publication13-Jul-2020

Correspondence Address:
Dr. Jitendra S Oswal
Department of Pediatrics, Bharati Vidyapeeth Medical College and Hospital, Pune . 411 043, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JPCC.JPCC_40_20

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Introduction: Confirmation of correct placement of the endotracheal tube (ETT) is as important as the procedure itself. Point-of-care ultrasound today is an indispensable modality in the intensive care unit (ICU) for augmenting the clinical assessment and guiding critical care procedures. In this study, we used point-of-care ultrasound to confirm ETT placement and compared the time taken to confirm the ETT placement by ultrasound and capnography (the gold standard of confirmatory ETT placement).
Materials and Methods: The current study was a prospective study done in a tertiary care teaching hospital. Children between 1 month and 18 years of age were included in the study. Airway ultrasound was done during the intubation procedure by placing the probe transversely over the suprasternal notch, and the confirmation of placement of the tube in the trachea was done by visualizing the absence of double trachea sign, and later confirmed by capnography. The average time taken for confirmation by ultrasound and capnography was determined.
Results: A total of 127 intubations were included. The average time taken for confirmation of placement of the ETT by airway ultrasound from the time of insertion of the laryngoscope blade was 26.8 ± 5.7 s, whereas by capnography, it was 35.5 ± 5.8 s. The study showed that airway ultrasound has a high sensitivity of 98.2% to detect tracheal intubation and specificity of 100% to detect esophageal intubation when compared to capnography.
Conclusion: Airway ultrasound can serve as a novel method of confirming the ETT placement in the pediatric ICU with comparable sensitivity, specificity with the added advantage of a significantly faster time of confirmation with respect to capnography.

Keywords: Airway ultrasound, capnography, double trachea sign, endotracheal intubation

How to cite this article:
Sarangi B, Reddy VS, Walimbe A, Oswal JS, Patro SK. Utility of upper airway ultrasound for confirmation of endotracheal tube placement in the pediatric intensive care unit setting. J Pediatr Crit Care 2020;7:179-85

How to cite this URL:
Sarangi B, Reddy VS, Walimbe A, Oswal JS, Patro SK. Utility of upper airway ultrasound for confirmation of endotracheal tube placement in the pediatric intensive care unit setting. J Pediatr Crit Care [serial online] 2020 [cited 2021 Jun 25];7:179-85. Available from: http://www.jpcc.org.in/text.asp?2020/7/4/179/289520

  Introduction Top

Endotracheal intubation is a seemingly simple yet decisive aspect of airway management in the face of acute life-threatening emergencies and a crucial aspect of resuscitation of a critically ill child in the intensive care unit (ICU). However, the procedure comes with its own set of challenges. Prolonged or repeated attempts at endotracheal intubation increase the risk of complications such as hypoxemia and hemodynamic compromise. The relevance of these possible complications is higher in infants and children who with a higher vagal tone[1] and relatively lower functional residual capacity[2] are more prone to hypoxemia related events. Multiple factors affect successful and smooth intubation. These factors are patient related, including airway anatomy itself, and the physiological aberrations and operator dependent such as experience, tube selection, and pharmacological choices. Hence, the correct placement of the endotracheal tube (ETT) must be facilitated in every possible way and even more with inexperienced operators. Conventionally, various methods have been described to check the correct placement of the ETT; direct visualization of the tube passing through the vocal cords during laryngoscopy, looking for an adequate and equal chest rise, 5-point auscultation, detecting the presence of misting in the tube, improving oxygen saturation and vital parameters, capnometry and capnography, fibreoptic bronchoscopy and chest X-ray. Of all the above, capnography and bronchoscopy are considered the gold standard in verifying the tracheal position of the ETT.

Sensitivity and specificity of capnography is 100% when there is a proper four-phase capnographic waveform [Figure 1].[3] Flatline on capnography is indicative of esophageal intubation but may also occur in cases with poor pulmonary blood flow such as massive pulmonary embolism, prolonged cardiac arrest, and the presence of an obstructed ETT. A capnograph with more than six waveforms confirms correct ETT placement. Considering the few limitations and the possibility of reduced availability of capnography in peripheral or smaller hospitals, there is a need for alternative techniques which can help in rapid and accurate confirmation of ETT in the trachea. Moreover, a technique providing real-time data may be slightly more viable than having to wait for confirmation via six capnograph waveforms as an unsuccessful attempt may not allow the luxury of those extra seconds in a critically ill or previously hypoxemic child.
Figure 1: Four phases of capnogram

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Point-of-care ultrasound has revolutionized practice in the ICUs around the world, and today is an essential modality offering several benefits in physiological and functional assessments of patients. It has also ensured a fourfold increase in the safety of procedures such as central line insertion. Today, portable ultrasound machines are readily available in Emergency Departments and ICUs of the majority of the centers irrespective of geographical location. Point-of-care ultrasound has been used to determine the correct placement of ETT by various methods, including direct confirmation by the presence of signs such as a snow-storm sign, comet-tail artifact with posterior shadowing and absence of double trachea sign (double tract sign). Indirect confirmation is also possible by visualizing lung sliding in the presence of seashore signs on M mode and bilateral diaphragm motion toward the abdomen.

In this study, we attempted to analyze the use of point of care ultrasound to visualize the airway to confirm the tracheal placement of ETT during intubation and compared the time taken to confirm the correct placement of ETT by airway ultrasound and capnography.

  Materials and Methods Top

It was a prospective single-center study conducted in a pediatric ICU of a tertiary care teaching hospital after approval from the institutional ethics committee.

The primary objective was to confirm the correct placement of ETT by verifying the absence of the double trachea sign using airway ultrasound. Double trachea sign [Figure 2] is the presence of two air mucosal interfaces after insertion of the ETT, thus indicating the presence of ETT in the esophagus (implying that correct placement of the ETT showed the absence of the double trachea sign). The secondary objectives were to determine the time taken to confirm individually the correct placement of ETT by airway ultrasound and capnography from the time of introduction of the laryngoscope blade in the mouth.
Figure 2: Double trachea sign present

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Children between 1 month to 18 years of age who required intubation in the Pediatric ICU were included in the study. In the interest of the safety of the patient, only the first attempt at intubation was considered. Children with anatomical abnormalities in the neck and those who were brought in gasping state or cardiorespiratory arrest were excluded. Written informed consent from parents was taken.

Three pediatric intensivists were recruited for the study. Roles were assigned as follows: The first one was responsible for intubation, second being the one who had received formal training in point of care ultrasound and the third who would keep record of the procedure and the time taken to confirm the endotracheal placement of the tube by ultrasound and capnography. Airway ultrasound was performed using the HLF 38 (Sonosite) linear probe with a frequency of 6–13 Mhz [Figure 3], while Smiths Medical transducer with Nihon Kohden monitors was used to measure capnography. The time taken for each confirmation by sonography and capnography was recorded with a stopwatch. A screening of structures surrounding the airway was performed before the procedure and the important structures including trachea and esophagus were identified. All the children were intubated as per rapid sequence intubation protocol based on local policy. The third intensivist noted the time when the laryngoscope blade was inserted into the mouth. The first intensivist performed the intubation while the second intensivist simultaneously performed airway ultrasound by placing the probe transversely over the trachea between the suprasternal notch and cricothyroid membrane in real time. Post intubation, correct placement of the ETT was considered with the absence of double trachea sign by point of care ultrasound, which was confirmed by capnography. ETT placement by capnography was confirmed when end-tidal CO2(EtCO2) was more than 4 mmHg at the end of six breaths with the characteristic waveform recorded. In the event of the presence of double trachea sign as well, capnograph was attached, and the absence of EtCO2 was confirmed following which re-intubation was attempted, and the second attempt was excluded [Figure 2] and [Figure 4].
Figure 3: HLF 38 (Sonosite) linear ultrasound probe with frequency of 6-13 Mhz used in our study

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Figure 4: Double trachea sign absent

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  Results Top

A total of 127 children who required intubation were included in the study as per the inclusion criteria. Children between 1 month and 18 years of age were included with a mean age of 5.41 ± 4.64 years [Table 1]. Male-to-female ratio was 1.44:1. The indication for intubation was either central nervous, respiratory, cardiorespiratory, or neuromuscular system disease and in some cases multifactorial. All intubations were visualized in real time by ultrasound and were subsequently confirmed with capnography, as mentioned above. The average time taken for confirmation of the placement of ETT by airway ultrasound from the time of insertion of laryngoscope blade was 26.8 ± 5.7 s whereas the average time taken for confirmation of placement of ETT by capnography from the time of insertion of laryngoscope blade was 35.5 ± 5.8 s (P < 0.001). Double trachea sign-on airway ultrasound was seen in 11 patients, which was in concurrence with capnography, indicating esophageal intubation (specificity 100%). Of the rest 116 cases, ultrasound detected tracheal intubation in 114 (sensitivity 98.2%) cases, whereas in the two cases were detected as esophageal intubation. This was because of the difficult visualization of the airway in the two infants, which were falsely picked up as double trachea sign positive.
Table 1: General characteristics of the subjects

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The distribution of confirmation of ETT placement by airway ultrasound was significantly associated with confirmation of ETT placement by capnography (P < 0.001), with a relatively higher Cohen's Kappa value of 0.908. Higher Cohen-Kappa value indicates that there is a higher to perfect level of agreement between capnography and ultrasound. Diagnostic efficacy indices such as sensitivity, specificity, positive predictive value and negative predictive value of ultrasound against capnography as a gold standard in detecting successful endotracheal intubation is 98.2%, 100.0%, 100.0%, and 84.6%, respectively.

  Discussion Top

Endotracheal intubations can be challenging even for expert clinicians during high-risk situations. Inadvertent esophageal intubation can lead to potentially life-threatening complications. In an era when rapid sequence intubation has emerged as the standard of care in most ICUs where we have different physiologically difficult airways to deal with, successful single-attempt intubation becomes a pivotal step in resuscitation and prevention of added morbidity. Rates for incorrect placement of ETT has been noted up to 25% in certain units.[4],[5],[6],[7],[8] The hemodynamic and hypoxemic complications of failed or repeated attempts at intubation may be catastrophic, thus making the verification of correct ETT placement a step as important as the procedure itself. Endotracheal intubation can be confirmed by various methods. Physical examination methods such as 5-point auscultation have inadequate sensitivity (94%) and specificity (83%) when used as an independent method of confirmation of ETT placement. Other physical examination methods include visualization of a chest rise with bag and tube ventilation and the presence of misting in the tube. Visualization of the tube passing through the vocal cords is possible with an experienced operator and serves as a method of confirming the correct placement of the ETT. Obtaining a chest radiograph serves as a useful method of detecting not just the presence of the tube in the trachea but also the position of its tip. However, it is time consuming and associated with radiation exposure. Fiberoptic bronchoscopy is also a reliable method of confirmation of ETT position, although not available easily in all ICUs. Confirmation by capnography is the most accurate and is a gold standard, according to the American College of Emergency Physicians (ACEP). ACEP states that capnography confirmation of endotracheal intubation approaches 100% sensitivity and specificity in the patient with an inflated cuffed ET tube and spontaneous circulation while in cardiac arrest sensitivity approaches 76%.[9]

The capnograph analyzer produces infrared rays that detect the CO2 molecules and generates a four-phase graph depending on the concentration of CO2 molecules in different periods of inspiration and expiration. The main disadvantage of carbon dioxide detectors is that they generate false-negative results in cases of poor pulmonary blood flow like massive pulmonary embolism, prolonged cardiac arrest, and the presence of an obstruction in the ETT. False-positive results are seen in patients when there is esophageal intubation after the consumption of large quantities of carbonated beverages and in the presence of high quantities of infrared absorbing gases like nitrous oxide used in operating theaters [Figure 5].[10]
Figure 5: Capnograph showing decreasing trend suggesting endotracheal tube obstruction/postesophageal intubation

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Point-of-care ultrasound has gained tremendous momentum as a diagnostic and therapeutic tool in the ICU. The fact that it is painless, noninvasive, reproducible, radiation-free, provides real-time data, and being relatively inexpensive makes it a valuable asset to possess and be familiar with. Some of the more routine applications of point-of-care ultrasound in ICUs include checking optic nerve sheath diameter as a marker of raised ICP, doing echocardiography for fluid responsiveness, lung ultrasound for detection of consolidations, atelectasis, effusions and pneumothorax, and abdominal ultrasound as a screening procedure in cases of blunt abdominal trauma. It has also augmented the safety of multiple critical care procedures, including central line insertions, pleural and peritoneal taps, and drain insertions. The majority of signs seen in lung ultrasound is artifactual and arises from the pleural line due to the presence of air underneath. Similarly, even though the larynx and trachea are filled with air, the inherent soft tissue around them creates a contrast making them suitable for visualization with ultrasound. All the structures surrounding the airway, including the cricoid, thyroid, and arytenoid cartilages are fairly echogenic whereas the air-mucosal interface of the trachea appears as a hyperechoic structure. Clinical applications of airway ultrasound that have emerged over the years include identification of difficult airway, identification of the cricothyroid membrane, prediction of appropriate ETT size, confirmation of endotracheal intubation and correct ETT depth, facilitation of percutaneous dilational tracheostomy, prediction of postextubation stridor and many others

Multiple methods of determining the correct placement of ETT using airway ultrasound have been described over the years, almost all of which have been reported by anesthesiologists and ICU Physicians as being highly sensitive and specific.[11] These methods, however, have not been studied as much in pediatric patients where the process of endotracheal intubation poses a major threat, if unsuccessful. To add to that, in the hands of an inexperienced operator trying to master endotracheal intubation, the risk of complications is much more. At the same time, doing airway ultrasound without an appropriate sized pediatric linear probe remains a challenge, especially in the infants. Thus, the ability of the various airway ultrasound methods to detect successful intubation requires a detailed study in the pediatric population to be used as an aid in the Emergency department as well as pediatric ICUs.

Patil et al. used ultrasound to detect the placement of the tube by checking the presence or absence of snowstorm sign as well as the double tract sign.[11] The snowstorm sign is basically the disturbance of tracheal air mucosal interface with comet tail artifacts or fluttering as the tube passes through the trachea while the double track sign refers to the appearance of a second air-filled structure adjacent to the trachea. They also used ultrasound to determine the depth of insertion of the ETT with saline-filled cuff technique. The study reported an overall sensitivity of airway ultrasound to confirm correct ETT placement as 96% with a positive predictive value of 100%.

Kabil et al. used tracheal ultrasound for detection of successful intubation in 40 patients by checking for the absence of double trachea sign and presence of a single air-mucosal interface with comet-tail artifact and posterior shadowing.[12] They used fibreoptic bronchoscopy to confirm the ETT placement. It was found that the sensitivity of tracheal ultrasound in the detection of ETT placement was 97.5%, with a specificity of 100%. The time consumed during tracheal ultrasound for the confirmation of the tube position was also recorded and was found to be shorter than the usual method of confirmation by fiberoptic bronchoscopy.

In a meta-analysis conducted by Das et al. it was found that trans-tracheal ultrasound used to detect ETT placement by comet-tail artifact technique had a sensitivity of 98% and specificity of 94%.[13] Gnanaprakasam and Selvaraj had proposed an ultrasound assessment of the subglottic region for determination of the external diameter of the uncuffed ETT size to be better than modified Cole's formula.[14] The subglottic diameter at the cricoid region was used to predict the uncuffed ETT size in children aged between 2–6 years and compared to another group where modified Cole's formula was used. They found that the incidence of appropriate tube selection was 74.7% in the ultrasound-based group as opposed to 45.3% in the modified Cole's formula group, thus labeling airway ultrasound as a better tool for appropriate tube size selection.

Sim et al. used the presence of bilateral lung sliding to confirm the endotracheal position which is an indirect way of determining ETT placement.[15] Lung sliding is seen on real time as the visceral pleura and lung move together in a direction opposite to the parietal pleura and chest wall as the lungs expand during inspiration. In their study, the presence of unilateral lung slide suggested main stem intubation, thus warranting repositioning of the tube. Rodríguez-Fanjul et al. used supra-sternal view and confirmed placement of ETT by lung ultrasound by visualization of the endotracheal tip in the tracheal region, presence of lung sliding, diaphragmatic excursion, and lung pulse sign.[16]

There are various methods of confirming an ETT placement by use of ultrasound, as shown in [Table 2]. Of all the methods, confirmation of the tube by the absence of a double tract or double trachea sign appears to be the most effective with a high sensitivity and specificity.
Table 2: Methods used for confirmation of endotracheal tube placement by ultrasound (A-M- air mucosa, endotracheal tube)

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Studies have shown that the time taken for confirmation of ETT placement by ultrasound was less than conventional methods such as fibreoptic bronchoscopy and capnography.[12] Similarly, the time taken to confirm the tube position using airway ultrasound was significantly lesser than that of capnography in our study, thus making it an invaluable tool in airway management where every second count.

Limitations of the study

Ours was a single-center study without a control group. A multi-center study with a larger sample size may be more ideal. The technique of ultrasound is often operator dependant in terms of skills and experience, and there exists an inter-observer variability, which requires consideration.

  Conclusion Top

In this study, the use of airway ultrasound to identify the correct placement of ETT by confirming the absence of a double trachea sign showed high sensitivity and specificity of 98.2% and 100%, respectively. We assume airway ultrasound is an easy, rapid, safe, and feasible method of detecting correct placement of ETT, which can further enhance the safety of the procedure of endotracheal intubation in the hands of an inexperienced operator and become potentially indispensable in ICUs.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Jones P, Dauger S, Peters MJ. Bradycardia during critical care intubation: Mechanisms, significance and atropine. Arch Dis Child 2012;97:139-44.  Back to cited text no. 1
Stocks J, Quanjer PH. Reference values for residual volume, functional residual capacity and total lung capacity. ATS Workshop on Lung Volume Measurements. Official Statement of the European Respiratory Society. Eur Respir J 1995;8:492-506.  Back to cited text no. 2
Silvestri S, Ladde JG, Brown JF, Roa JV, Hunter C, Ralls GA, et al. Endotracheal tube placement confirmation: 100% sensitivity and specificity with sustained four-phase capnographic waveforms in a cadaveric experimental model. Resuscitation 2017;115:192-8.  Back to cited text no. 3
Schwartz DE, Matthay MA, Cohen NH. Death and other complications of emergency airway management in critically ill adults. A prospective investigation of 297 tracheal intubations. Anesthesiology 1995;82:367-76.  Back to cited text no. 4
Neumar RW, Otto CW, Link MS, Kronick SL, Shuster M, Callaway CW, et al. Part 8: Adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122:S729-67.  Back to cited text no. 5
Jones JH, Murphy MP, Dickson RL, Somerville GG, Brizendine EJ. Emergency physician–verified out-of-hospital intubation: Miss rates by paramedics. Acad Emerg Med 2004;11:707-9.  Back to cited text no. 6
Katz SH, Falk JL. Misplaced endotracheal tubes by paramedics in an urban emergency medical services system. Ann Emerg Med 2001;37:32-7.  Back to cited text no. 7
Wang HE, Mann NC, Mears G, Jacobson K, Yealy DM. Out-of-hospital airway management in the United States. Resuscitation 2011;82:378-85.  Back to cited text no. 8
Verification of endotracheal tube placement. Ann Emerg Med 2016;68:152.  Back to cited text no. 9
Sum Ping ST, Mehta MP, Symreng T. Reliability of capnography in identifying esophageal intubation with carbonated beverage or antacid in the stomach. Anesth Analg 1991;73:333-7.  Back to cited text no. 10
Patil V, Bhosale S, Kulkarni A, Prabu N, Bhagat V, Chaudhary H, et al. Utility of ultrasound of upper airway for confirmation of endotracheal intubation and confirmation of the endotracheal tube position in the intensive care unit patients. J Emerg Crit Care Med 2019;3:15.  Back to cited text no. 11
Kabil AE, Ewis AM, Al-Ashkar AM, Abdelatif MA, Nour MO. Real-time tracheal ultrasonography for confirming endotracheal tube placement. Egypt J Bronchol 2018;12:323.  Back to cited text no. 12
  [Full text]  
Das SK, Choupoo NS, Haldar R, Lahkar A. Transtracheal ultrasound for verification of endotracheal tube placement: A systematic review and meta-analysis. Can J Anaesth 2015;62:413-23.  Back to cited text no. 13
Gnanaprakasam PV, Selvaraj V. Ultrasound assessment of subglottic region for estimation of appropriate endotracheal tube size in pediatric anesthesia. J Anaesthesiol Clin Pharmacol 2017;33:231-5.  Back to cited text no. 14
[PUBMED]  [Full text]  
Sim SS, Lien WC, Chou HC, Chong KM, Liu SH, Wang CH, et al. Ultrasonographic lung sliding sign in confirming proper endotracheal intubation during emergency intubation. Resuscitation 2012;83:307-12.  Back to cited text no. 15
Rodríguez-Fanjul J, Balcells Esponera C, Moreno Hernando J, Sarquella-Brugada G. Lung ultrasound as a tool to guide the administration of surfactant in premature neonates. An Pediatr (Barc) 2016;84:249-53.  Back to cited text no. 16


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