Author: Kirstin Weerdenburg, MD FRCPC 

Secondary Author: Emma Burns, MD FRCPC 

Reviewer(s): Melanie Willimann, MD FRCPC; Mark Bromley, MD FRCPC; Julia Stiz, MSc, RDCS, RDMS 

Summary

• POCUS has shown to be a fast, effective and safe adjunct to other ETT position confirmatory methods   

• To confirm ETT placement, the technique can be performed dynamically or statically using a high frequency linear probe placed in the transverse plane at the level of the suprasternal notch  

• With endotracheal intubation, the esophagus should be collapsed​.​​ Only​​ one air filled structure should be seen (trachea) and the snowstorm sign can be seen dynamically.  

• With esophageal intubation, the double tract (double trachea sign) will be seen  

• To confirm ETT placement, ultrasound can be used to assess lung sliding, ​and ​cuff placement​.​ ​     ​  

• Ultrasound can be used to identify the location of the cricothyroid membrane​ to facilitate surgical airway management.​  

Identification of the cricothyroid membrane​ to facilitate surgical cricothyrotomy​​   

Cricothyrotomy is an advanced skill that is rarely performed by physicians. Use of ultrasound should never delay definitive airway establishment. Expert surgical consultation should be sought early.  

 

Technique:

Step 1: Place the probe in the longitudinal plane at the suprasternal notch (Figure 9) and identify the tracheal ring of pearls (Figure 10, purple circles) 

Figure 9: Airway POCUS using the linear probe in a supine patient  

 

Step 2: Move the probe cephalad until you identify: 

– The cricoid: a larger pearl with posterior acoustic shadowing (Figure 10, green oval) 

– Thyroid cartilage: cephalad to the cricoid, a hyperechoic structure with hypoechoic shadow (Figure 10, Blue oval) 

 

Practice Pearl: 

Like many structures in children, the cartilage is less calcified, appearing darker (hypoechoic) on ultrasound with minimal shadowing compared to adults. Nevertheless, the positional relationships—thyroid cartilage, cricothyroid membrane, cricoid cartilage—remain the same, so you can still use the same “string of pearls” approach and carefully identify the membrane for procedural marking. The “pearls” may be a smaller and dimmer in younger pediatric scans compared to older patients.

 

Step 3: Identify the cricothyroid membrane – in between the cricoid and thyroid cartilage (Figure 10, yellow line) 

 

Step 4: Mark the skin and use this as a static landmark for the surgical airway 

 

Figure 10: Longitudinal plane over the cricothyroid membrane (yellow line), thyroid cartilage (blue circle), cricoid cartilage (green circle) and tracheal rings string of pearls (purple circles). 

Evaluation of ETT depth

 

Evaluation of Lung Sliding

​​The depth of ETT insertion can also be evaluated using lung POCUS. ​Normal lung sliding indicates aeration of the lung. The movement caused by inflation of the lung can be seen as the visceral and parietal pleura move and is called lung sliding or shimmering. As such, presence​​​​​ of bilateral lung sliding indicates endotracheal intubation with an ETT positioned above the carina. ​ The absence of lung sliding suggests the lung is not being ventilated and raises suspicion for esophageal intubation. If unilateral lung sliding is seen, it can suggest mainstem intubation [22]. ​​​  

 

Technique

​Lung ​u​​​ltrasound can be performed with the patient in ​the ​supine position, using a linear or curvilinear​​ probe placed in the longitudinal plane on the anterior chest of the patient at the midclavicular line​.​ ​​​​​​​​​This is performed on both the left and right anterior chest walls. ​The ​relevant​​​ anatomic structures for this view are the pleural line, chest wall musculature and the ribs and their ​acoustic ​shadows (Video 3)  

​​​Important limitations to using lung sliding for confirmation of ETT depth include diseases and conditions that affect the pleura and therefore lung sliding on POCUS. This includes pneumothorax, ARDS, pneumonia, pleural disease and contralateral lung sliding despite mainstem intubation because of retrograde air movement.

 

Video 3. Lung ultrasound video performed using a linear probe placed in the longitudinal plan on the anterior chest of the patient at the midclavicular line demonstrating pleural line with normal sliding  

Video 4. Lung ultrasound video performed using a linear probe placed in the longitudinal plane on the anterior chest of the patient at the midclavicular line demonstrating absent lung sliding  

 

M-Mode can also be used to confirm the presence of lung sliding. In a normal lung where lung sliding is present, the “sand on the beach” or “seashore” sign can be observed (Figure 8A). Conversely, absence of lung sliding will create the “stratosphere” or “barcode” sign (8B).  

Figure 8. Use of M-mode to identify A) presence (​seashore​​ sign) or B) absence (stratosphere sign) of lung sliding   

 

For more information on lung sliding and lung PoCUS, please revisit the KidSONO Pneumothorax Module. 

Confirmation of ETT Position

Patient position: Supine 

Probe Placement: Place the probe in the transverse plane at the level of the suprasternal notch (Figure 6) and identify the normal sonoanatomy including thyroid, trachea, and esophagus. 

Scanning Tip: The position of the esophagus can be variable, adjust your scanning plane by slightly sliding and tilting the probe left and right to identify the position of the esophagus.  

 

Figure 6. Airway POCUS using the linear probe in a supine patient in the with corresponding sonographic appearance  

 

Dynamic Technique

Step 1: The dynamic evaluation Identification of normal sonoanatomy should be done before the intubation is started.  

Step 2: During endotracheal intubation, assess for motion artefact (the snowstorm sign)  

– Motion artefact will be visualized as the ETT is advanced in the trachea (Video 1).

– If the tube is inadvertently placed in the esophagus, a second air filled structure with comet tail artifact will appear, this is also called double trachea or double tract sign (Video 2).  

 

Video 1: Dynamic ETT technique with proper tube placement showing snowstorm sign

Video 2: Dynamic ETT technique with improper tube placement within the esophagus (double tract sign).

 

 

Static Technique

Step 1: Prior to tube placement, static evaluation of tube placement is performed by placing probe in the transverse position at the suprasternal notch and identifying the normal sonoanatomy.  

Step 2: Once the intubation is completed, the ultrasound is repeated.  

– The image interpretation will be the same as the dynamic technique.  

– With esophageal intubations, a second air filled structure with comet tail ​artifact​ will appear revealing ​the ​double tract ​sign (Figure 7)​.   

 

Figure 7. Ultrasound position above the ​suprasternal​​   ​notch showing comet tail artifact (c); and ​double-tract​ sign (d) [21]   

Technique Overview

 

Step 1:  Obtain baseline view of the sonoanatomy of the patient’s airway prior to intubation

• Place the high frequency linear probe above the patient’s suprasternal notch in the transverse plane​  
• Identify the trachea, thyroid cartilage, esophagus  

 

Step 2: Choose between static ​and​​ dynamic technique for Airway POCUS ​     ​  

• Static: intubate and repeat the ultrasound​.​​ ​ ​Identify ​the double tract sign if present  
• Dynamic: keep the probe ​position​ed in the suprasternal notch. Watch ​for the snowstorm​ (motion artifact) and double trachea ​​signs​.​  

 

Step 3: Assess for the depth of the ETT 

• Evaluate lung sliding  

 

Step 4: If urgent cricothyroidotomy is required, consider ultrasound identification of the cricothyroid membrane

 

A comprehensive explanation of each step is provided in the sections to follow 

What Am I Looking At?

Key anatomical structures relevant to airway management include the trachea, esophagus, thyroid gland, thyroid cartilage, vocal cords, cricothyroid membrane, and cricoid cartilage. 

In cross-section, the trachea is midline, and the esophagus lies posterolateral, usually to the left. The thyroid gland sits anteriorly, partially wrapping around the trachea (Figure 1) 

Figure 1: Cross sectional anatomy on the neck in axial plane 

 

Additional anatomical landmarks relevant for surgical airway planning, from cephalad to caudad, include the thyroid cartilage, cricothyroid membrane, cricoid cartilage and trachea (Figure 2) 

 

Figure 2: Longitudinal Anatomy relating to surgical airway planning.  

 

Ultrasound Anatomy Review

The airway can be evaluated by ultrasound from the suprahyoid area to the suprasternal notch in both the transverse and longitudinal planes (figure 3).  

The transverse view is most used to confirm the location of the ETT (Figure 4), but the longitudinal view can aid in landmarking when planning a surgical airway (Figure 5).    

 

Figure 3. Reproduced from Lin et al, Diagnostic 2023 [19]  

 

Transverse view: 

In this view, we see the trachea centrally, and the esophagus lies posterolateral (left). The thyroid gland sits anteriorly wrapping around the trachea. 

Figure 4: Transverse plane over the suprasternal notch showing the trachea (purple circle), esophagus (yellow circle) and thyroid (blue area) with the air-mucosa interface (green line).  

 

Longitudinal View 

In this view, the thyroid cartilage, cricothyroid membrane, cricoid cartilage and tracheal rings (string of pearls) are seen. 

Figure 5: Longitudinal plane over the cricothyroid membrane (yellow line), thyroid cartilage (blue circle), cricoid cartilage (green circle) and tracheal rings string of pearls (purple circles).

Indications

• Confirmation of ETT position 
• Evaluation of ETT depth
• Identification of cricothyroid membrane

 

In the context of airway management, ultrasound provides a rapid and reliable method for confirming endotracheal tube position, assessing depth, and identifying key anatomical landmarks like the cricothyroid membrane. Whether in the emergency setting or during elective intubation, point-of-care ultrasound can improve clinical decision-making, reducing reliance on traditional confirmation methods alone.   

 

Equipment

• Ultrasound machine   
• High frequency linear probe or curvilinear probe for obese patients  
• Ultrasound Gel   
• Endotracheal tube       ​  

Introduction

​​​​Endotracheal intubation is an essential procedure in​​ the care of critically ill children. ​Immediate and accurate​ confirmation of ETT (endotracheal tube) position and depth is essential ​for ensuring ​adequate ventilation and oxygenation. Misplaced endotracheal tube insertions may lead to​ potentially life-threatening complications including​ inadequate ventilation, mainstem intubation, lung collapse, pneumothorax, hypoxia and cardiorespiratory arrest [1].    

Traditional methods to confirm ETT placement ​such as​ auscultation and visualization of condensation in the ETT are not consistently reliable [2, 3]. ​According to the American Heart Association and Pediatric Advanced Life Support guidelines, e​nd-tidal and colorimetric capnography ​are​ the current gold standard for assessment of endotracheal intubation [4, 5].  ​Unfortunately, ​capnography ​may be​ limited in cardiac arrest due to poor ventilation and poor lung perfusion ​which limits the​ delivery of carbon dioxide [6]. ​While ​direct visualization of the endotracheal tube passing through the vocal cords is helpful to confirm ETT placement​,​ ​it​ is not always possible in ​complex​ airway situation​s​.   

Despite the aforementioned methods esophageal ​intubation still​​​ ​occurs​ in up to 4% of adult intubations [7] and is more common during cardiopulmonary resuscitation ​with a reported rate of ​10% [8, 9]. The failure rate at first attempt endotracheal intubation in​​ children is even higher (41%) [1].   The depth o​f​ ETT insertion is often evaluated using chest radiographs [10]. This may delay patient care if access to radiography is limited and exposes patients to radiation.  

 Point-of Care Ultrasound (POCUS) of the airway can also be a useful adjunct to help clinicians confirm ETT position and depth and to evaluate the anatomy ​prior to performing a ​surgical airway.  

  

Why Point-Of-Care Ultrasound?   

Airway POCUS allows clinicians to visualize the position of the ETT in real time. ​This technique​ can be performed ​both ​during (dynamic phase) ​and​ following (static phase) endotracheal intubation​.​​ ​Further, recent meta-analyses have ​shown ​POCUS to ​have high diagnostic accuracy with a sensitivity of 98% and a specificity of 95% ​when​ used for ETT confirmation in the adult population [11].

Airway POCUS for confirmation of ETT position is ​rapid. It can​ ​typically ​be performed within 9 seconds by expert sonographers and 36s by novice sonographers [12]. ​On average​​,​ ​the ​time to confirm ETT position using ultrasound is less than 10 ​seconds​​ [8​, 13].  Moreover, the learning curve for distinguishing between esophageal and endotracheal intubation on imaging is steep and rapid. Emergency physicians ​have demonstrated the ability​​ to quickly (average 4s) and accurately (90%) identify the correct placement of the ETT on ultrasound videos and images [14].  

Airway POCUS correlates with capnography in patients who are not in cardiac arrest [15] and can be performed non-invasively during cardiopulmonary resuscitation ​in arrest scenarios ​when capnography results are not reliable [8].   

​​​In the context of surgical airways, ​​​POCUS can also be used to identify the cricothyroid membrane in children [16]. Ultrasound outperforms digital palpation of the cricothyroid membrane in children [17]​​​.​​​​​ ​Furthermore, its application ​has been ​linked to​​​ improve​d​ success ​rates​​​ ​in ​correct cricothyroid tube placement in adult​ patients​​​[18, 19]. However, it ​is important to note that using ultrasound in this context can be more time consuming. Ultrasound use will typically take ​​​​​17s​,​ ​​compared to traditional palpation which takes about 8s [20]​.​​​​ This time cost ​may be ​worthwhile​​​ in patients with higher BMI​ where palpation may be more difficult or in the anticipated difficult airway when there is sufficient time prior to intubation​.   

Airway POCUS has also been proposed as a risk prediction tool for difficult laryngoscopy in adults. Pediatric literature on prediction of ​airway difficulty​​​ ​​is scant and beyond the scope of this module.   

 

 

 

Primary Author: Jade Seguin, MD FRCPC  

Secondary Author: Simon Bichara Allard, MD   

Reviewer(s): Mark Bromley MD FRCPC , Melanie Willimann MD FRCPC, Jackie Harrison MD FRCPC , Julia Stiz MSc RDMS