Technique

 

Figure 1: The inverted “U” technique to identify ileocolic intussusception 

 

While several techniques have been described, we will focus on the one known as the “Inverted U” [figure 1]: 

1. With the patient supine and in a position of comfort (possibly in the parent’s lap) place probe in the right lower quadrant with the probe marker aimed to the patient’s right while in the transverse plane. The psoas muscle and iliac vessels can be identified as the starting landmark on the right of the screen.
2. Move the probe laterally until the cecum is identified. From here you will follow the path of the large intestine to identify any evidence of intussusception.
3. With the probe in the transverse plane, slowly move the probe superiorly to the right upper quadrant until the liver and gallbladder are visualized as landmarks—following the course of the large bowel.
4. Rotate the probe 90 degrees clockwise so the probe marker is aimed toward the patient’s head and move the probe along the epigastrium to the left upper quadrant in the sagittal or longitudinal plane.
5. Rotate the probe 90 degrees counterclockwise so the probe marker is pointed to the patient’s right and move the probe inferiorly towards the left lower quadrant.
6. If an intussusception is visualized, confirm it’s presence in two planes, measure the AP diameter in the transverse plane and apply color Doppler to assess for blood flow and possible ischemia.

 

Scanning Tips: 

– Graded compression can be applied to help displace bowel gas or air and improve visualization of intussusception. 

– Intussusception is most often found just deep to the abdominal wall on the right side of the abdomen. 

 

Indications

Clinical suspicion of intussusception, which could include any of the following signs/symptoms: 

• Colicky or intermittent abdominal pain 

• Vomiting 

• “Currant jelly stool” 

• Palpable abdominal mass 

• Acute abdomen 

• Lethargy or altered level of consciousness 

 

Equipment

• Gel 
• High frequency linear probe (preferred, although low frequency curvilinear probe can be used for older children) 

 

Intussusception is a concerning differential diagnosis in young children presenting with abdominal pain. Misdiagnosis is common, as classic clinical symptoms of intussusception are often not present and physical examination findings are non-specific. Delay in diagnosis can lead to significant morbidity and mortality. Ultrasound is the diagnostic modality of choice and POCUS is emerging as the standard screening modality for intussusception, and unlike barium or air contrast enema, it does not carry the risk of bowel perforation. 

 

Why Ultrasound?

In children presenting with intussusception, plain radiographs often do not show any abnormalities [1]. A recent systematic review and meta-analysis found that point of care ultrasound had excellent sensitivity of 98% and specificity of 98% in detecting intussusception in children, and that the diagnostic accuracy of POCUS for intussusception was not significantly different from radiology-performed ultrasound. [2] When POCUS is used by novice sonographers, studies have reported an acceptable sensitivity of 85-89% but an excellent specificity of 97-98% with narrower confidence intervals. [3,4] Thus, POCUS is described as “rule in” test, an attractive modality to diagnose intussusception at the bedside rapidly and accurately, while decreasing the length of stay in the Emergency Department and expediting reduction. [5]  

 

 

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).