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

 

Summary

Importance of PoCUS:

PoCUS is essential for quick and accurate diagnosis. Cardiac ultrasound can help in the characterization of shock, hemodynamics, and respiratory failure in critically ill patients, leading to more targeted and timely interventions. 

 

Standard Cardiac Views:

The module covers techniques for obtaining each of the five standard cardiac windows: parasternal long axis (PLAX), parasternal short axis (PSAX), apical four chamber, subxiphoid four chamber, and IVC views. Each of these windows offers distinct clinical information and can be used for various clinical assessments, including left ventricular function, pericardial effusions, ventricular size comparison, and IVC assessment for fluid status. 

The following charts summarize the key information for each view,  in both cardiology and EM conventions:

Subxiphoid IVC View

Technique

• To obtain a view of the IVC, the probe is placed in the subxiphoid space similar to the subxiphoid cardiac view but with the ultrasound beam pointed deep towards the patient’s back. 

• To obtain a longitudinal view the probe indicator should be directed towards the patient’s head. The probe should be heeled or rocked towards the patient’s head so that both the hepatic veins draining into the IVC and the IVC draining into the right atrium are visualized (Figure 27).

• To obtain a transverse view the probe indicator is directed to the patient right in emergency convention and the patient’s left in cardiology convention. 

• Adjust the depth to ensure the full IVC is seen on the bottom of the screen. 

• Adjust gain to ensure that blood within the IVC appears black. 

 

Figure 26: IVC External Landmarking

 

Note: Emergency vs Cardiology convention

The subxiphoid IVC long axis view will vary in appearance on the screen whether you are using emergency or cardiology convention. With the probe marker directed to the patient’s head the images on screen will appear as mirror images of each other depending on whether your screen marker is on the left, as in emergency convention, or on the right as in cardiology convention. In the emergency convention the IVC can be seen draining into the heart on the left side of the screen, in cardiology convention this will appear on the right hand side.

The subxiphoid IVC transverse view will appear the same on the screen whether you are using emergency or cardiology convention. This is because both the probe markers and screen markers are oriented opposite, resulting in the same net image on screen 

Figure 27. IVC View Emergency Medicine Convention. 

Figure 28. IVC View Cardiology Convention. 

Tips: 

• This window can be challenging to obtain in patients with obesity, abdominal pain or lots of bowel gas as it uses the liver as an acoustic window to view the heart.  

• If able, having the patient bend their legs can help relax the abdominal wall. Asking the patient to take a deep breath in can also bring the diaphragm and heart towards the probe. 

• It is common to mistake the aorta for the IVC as they are parallel and in close proximity. To avoid this, the IVC should be tracked until it is seen entering the RA. Additionally, the aorta should be pulsatile, but sometimes aortic pulsations can transmit to the IVC. If in doubt, visualize both in the transverse plane or use color doppler to determine direction of blood flow. 

 

What Am I Looking At?

For the longitudinal view of the IVC, the image will display the liver, hepatic veins (draining into IVC), and the IVC as it drains into the right atrium (Figure 29).

If starting from an A/P or cross-sectional of IVC, both the IVC and the abdominal aorta will be seen anterior to a thoracic vertebral body. The abdominal aorta will be anterior and to the (patient’s) left of the vertebral body, while the IVC will be anterior and to the (patient’s) right of the vertebral body (Figure 30)

Figure 29: IVC View in the EM Convention 

 

Figure 30: Subxiphoid IVC transverse view, emergency medicine convention

Clinical Utility

This view allows the provider to assess size, distensibility or collapsibility of the IVC as well as to make comparison of the IVC and aorta diameter. 

Subxiphoid Four Chamber View

Technique

• In this view, the heart is imaged in a coronal plane but from a different angle than the apical four-chamber view (Fig 21).

• The probe should be held “overhand” with the hand on top of the probe.

• Place the probe in the subxiphoid space with the ultrasound beam pointing up towards the patient’s left scapula.   

• In emergency convention the probe marker is pointing towards the patient’s right (figure 22A) and in cardiology convention it is directed towards the left (Figure 22B).

• Depth should be adjusted to ensure visualization of the left ventricle and posterior pericardium 

• Gain should be adjusted so the myocardium appears grey and blood black. 

 

Figure 21: Anatomical coronal view of the heart from the SubXiphoid position

 

 

Figure 22. Subxiphoid external landmarking EM vs Cardiology Convention with overhand grip

 

 

Note: Emergency vs Cardiology convention

The subxiphoid four chamber view will appear the same on the screen whether you are using emergency or cardiology convention. This is because both the probe markers and screen markers are oriented opposite, resulting in the same net image on screen 

Figure 23: Subxiphoid View EM Convention.     

Figure 24: Subxiphoid View Cardiology Convention. 

Scanning Tips: 

• This window can be challenging to obtain in patients with obesity, abdominal pain or lots of bowel gas as it uses the liver as an acoustic window to view the heart.  

• Try using lots of gel and exerting the minimal needed pressure, although sometimes significant pressure is needed. 

• If able, having the patient bend their legs can help relax the abdominal wall. Asking the patient to take a deep breathing in can also bring the diaphragm and heart towards the probe. 

• If struggling with bowel gas, try moving the probe inferiorly and to the patient’s right to get a window through the liver. 

• Fan the probe, flattening it out until the heart comes into view on the screen. 

What Am I Looking At?

In this view a coronal view of the heart is obtained. In the near field just below the probe often the acoustic window of the liver can be seen. Just deep to that is the diaphragm upon which the right ventricle lies. Deep to that the left ventricle can be seen. In this view the ventricles are on screen right and the atria are on screen left. 

Figure 25: Video of the Subxiphoid 4 chamber view

 

Clinical Utility

This view is the best view to appreciate pericardial effusions. As it is also a four chamber view it also allows for assessment of the left and right ventricular size and function. Importantly this may be the only view available in emergent situations such as ongoing CPR so as not to interfere with chest compressions. 

 

Apical Four Chamber View

Technique

• In this view the heart is imaged in a coronal plane (Figure 16) 

• To obtain an apical four-chamber (A4C) view, the probe is placed over the apex of the heart which is usually located in the vicinity of the left nipple (or inframammary line in females), in the 4th-5th intercostal space and the ultrasound beam directed towards the patient’s right shoulder. 

• In emergency convention the probe marker is pointing towards the patient’s right hip and in cardiology convention it is directed towards the left shoulder (Figure 17)

• Once you reach the apex of the heart, as indicated by the left ventricle decreasing in size, tilt the tail of the probe down towards the patient’s feet. 

• Depth should be adjusted to ensure visualization of the atria in the far field 

• Gain should be adjusted so the myocardium appears grey and blood black. 

• The ideal view should have the IVS centered on the screen and from the top to bottom on the screen, parallel to the ultrasound beam. 

 

Figure 16: Coronal view of the heart from the apical window 

 

Note: Emergency vs Cardiology convention 

The apical four chamber view will appear the same on the screen whether you are using emergency or cardiology convention. This is because both the probe markers and screen markers are oriented opposite, resulting in the same net image on screen 

Figure 17. External Landmarking for A4C View Emergency Medicine Convention (A) vs Cardiology Convention (B)

 

Scanning Tips: 

• This window can be challenging to obtain, especially in mechanically ventilated patients, use lots of gel and make small circular movements until the best window is obtained. 

• If struggling to find a window, lying the patient in the left lateral decubitus position will aid in pulling the heart against the chest wall and the lung away from it 

• An adequate view should have the apex in the near-field, the ventricles appearing elongated with a straight interventricular septum running vertically down the screen. 

• The position of the cardiac apex is highly variable. One method used to reliably obtain an adequate A4C is to begin with a high-quality PSAX and slide the transducer inferolaterally keeping the LV centered on the screen before tilting the face of the probe upwards to the right shoulder to view the heart in a coronal plane 

What Am I Looking At

In this view a coronal view of the heart is obtained. In the near field just below the probe the apex with the RV visualized below on screen left and the LV on screen right. Deep to the ventricles the mitral and tricuspid valves can be separating the ventricles from the atria which lie in the far-field. The intraventricular and atrial septums can be seen running vertically on the screen from the near to far field, dividing the right and left sides of the heart. 

Figure 18: A4C coronal view of the heart, illustrating the right and left atria (RA, LA), right and left ventricles (RV, LV), interventricular septum (IVS), interatrial septum (IAS), mitral valve (MV), and tricuspid valve (TV).

 

Figure 19: Apical Four Chamber View EM Convention 

 

Figure 20. Apical Four Chamber View Video Clip 

 

Clinical Utility

The apical four chamber view provides a wealth of information including global assessment of LV and RV function and size. It is the best view to compare ventricular sizes. This is another view in which pericardial effusions can be seen. The A4C view also allows two-dimensional evaluation of the tricuspid and mitral valves. 

 

Parasternal Short Axis View

Technique

• The easiest way to find the PSAX view is to optimize your PSLX view and while maintaining the probe position on the chest wall rotate your probe 90 degrees clockwise (for cardiology convention) (Figure 6) or counterclockwise (for radiology convention) (Figure 7).  

• The ultrasound probe should be placed immediately patient left of the sternum at at the level of the 3rd of 4th intercostal space 

• To obtain a cross-sectional view of the heart the probe marker is directed to the right hip in emergency convention or the left shoulder in cardiology convention (resulting in the same image on the screen) 

• Depth should be adjusted to ensure the posterior pericardium is visible in the far field 

• Gain should be adjusted so that the myocardium appears grey, and blood appears black 

• The probe should be adjusted using small movements of sliding, sweeping and rotation to optimize the view, ensuring the LV appears circular on screen and not oval or elongated. 

Figure 6. External Landmarking for parasternal short cardiology convention 

Figure 7. External Landmarking for parasternal short EM convention 

Note: Emergency vs Cardiology convention: 

The parasternal short axis view will appear the same on the screen whether you are using cardiology or emergency convention. This is because both the probe markers and screen markers are oriented opposite, resulting in the same net image on screen 

Figure 8: Parasternal Short View Cardiology Convention. 

 Figure 9: Parasternal Short View EM convention. 

Scanning Tips: 

• Sometimes it is necessary to slide the probe to different intercostal spaces to find the best window to view the heart, especially mechanically ventilated patients. If struggling, try each intercostal space starting from below the clavicle 

• If struggling to find a window, lying the patient in the left lateral decubitus position will aid in pulling the heart against the chest wall and the lung away from it 

• The easiest way to find the PSAX view is to optimize your PSLX view and while maintaining the probe position on the chest wall rotate your probe 90 degrees clockwise. 

• Caution is required to avoid probe sliding when rotating the probe from the PLAX to obtain the PSAX view and to rotate 90 degrees to prevent an oblique view. Two hands can be used for this technique; one to rotate the probe while the other hand secures the position of the probe on the patient’s chest 

What Am I Looking At?

In this view a cross section of the short axis of the heart is obtained. Most prominent is the circular LV, appearing as a donut in the middle of the screen. In the near field just below the probe the crescent-shaped right ventricle is visible, “hugging” the LV. The LV and RV are separated by the interventricular septum (Figure 10). 

Figure 10: Parasternal Short View Labeled

 

PSAX Imaging Planes

Different imaging planes are available from the PSAX.  Progressive sliding (angling if the window does not allow sliding) of the face of probe from the patient’s right shoulder toward the patient’s left hip will successively produce images from the base through the apex of the heart. Here we will focus on the fundamental images obtained from the PSAX, starting with structures most superiorly at the right shoulder and progressively lower to the left hip: 

​​Aortic valve level: The aortic valve will be seen as a “Mercedes Benz” sign as the three leaflets of the AV close to produce the three-pointed star associated with the car logo. An ideal view will also include the RA, TV, RV, atrial septum and LA. (Figure 11) 

Figure 11: Parasternal Short Aortic Valve Level

 

Mitral valve level: From the AV view, the ultrasound beam is tilted inferiorly until the mitral valve is visualized. The MV has been described as a “fish-mouth” with anterior and posterior mitral leaflets representing the upper and lower lip respectively (Figure 12). In this view, the RV, IVS, and LV are also visualized. (Figure 13) 

Figure 12: Parasternal Short Zoomed Mitral Valve

Figure 13: Parasternal Short Mitral Valve View Video with color in the cardiology convention

 

Mid-papillary level:  Further tilting of the ultrasound beam in an inferior direction will produce the mid-papillary image. The papillary muscles appear as slightly hyperechoic “knobs” protruding from the inferior aspect of the LV. The posteromedial papillary muscle (PM) position will vary between the 6-9 o’clock positions, while the anterolateral PM is usually seen between the 3-6 o’clock position. The RV, IVS, and LV are also visualized. (Figure 14) 

• In the critically ill patient, the mid-papillary view has the highest yield and provides the best assessment of global LV function and any wall motion abnormalities. This is the gold standard view for evaluating the shape of the interventricular septum. 

Figure 14: Parasternal Short Mid-Papillary View 

 

Apex: Finally, further tilting the ultrasound probe inferiorly until the PMs are no longer seen will generate a view of the LV apex. The RV and IVS are also visualized. (Figure 15) 

Figure 15: Parasternal Short Apex View 

Clinical Utility

The PSAX view at the mid-papillary level provides global assessment of LV function and any LV wall abnormality. The mid-papillary view also allows visualization and assessment of the interventricular septal shape when assessing the right side of the heart.