Images and Text Genevieve Carbonatto
Ultrasound can be used as an adjunct to directly visualising endotracheal tube placement. The linear probe is placed in the transverse position with the index marker pointing to the right on the neck above the sternal notch. The structures are identified. These include the trachea and the oeseophagus. The oesophagus is collapsed and therefore may be difficult to visualise. It lies to the right of the trachea on the screen deeper than the anterior border of the trachea. The trachea is identifiable by it’s hyperechoic cartilagenous rim which casts an acoustic shadow. Air within the trachea produces a dirty shadow. This is a reverberation artifact.
When the trachea is intubated correctly there is an increase in acoustic shadowing just beneath the tracheal semicircular hyperechoic rim. As intubation occurs movement can be appreciated within the trachea anteriorly associated with more reverberation artifacts. To confirm placement it is possible to shake the ET tube and see movement within the trachea.
When the oesophagus is intubated, a curvilinear structure which mimics the trachea, is seen to the right of the trachea. This is the ET tube within the oesophagus. This has been referred to as the double track sign. Note that the value of ultrasound is in real time sonography. It is seeing the ET tube enter the oesophagus and then immediately identifying it’s curvilinear structure. Ultrasound to check for tube placement should therefore be done as the patient is being intubated. If you put a probe on after intubation to check for correct tube placement it may be difficult to appreciate the “double tracks”
The insertion of a bougie will produce a similar effect to that of an endotracheal tube. A subtle movement will be visualised below the hyperechoic curvilinear tracheal cartilage as the bougie is inserted in the trachea.
It is easier to appreciate oesophageal bougie insertion as the deformity of the oesophagus by the bougie is visualised in real time.
Limitations of the use of ultrasound to check for tube placement:
- The oesophagus may be deep to the trachea in which case oesophageal intubation will not be detected.
- If you have the angled up rather than at 90 degrees to the trachea, the anterior border of the trachea may be ill defined making the identification of proper tube placement through the trachea more difficult. In this case check by shaking the tube and movement will be seen within the trachea if tracheal intubation is successful
- If the probe is placed on the neck more towards the patient’s right, the oesophagus may not be visualised and oesophageal placement may be missed
- Because the oesophagus lies deeper in the neck than the trachea ensure that you have enough depth to see it.
- Ensure that ultrasound is being used to identify tube placement during the procedure as it is sometimes difficult to identify oesophageal intubation after the procedure
- ACEP guidelines Tips and Tricks: Airway Ultrasound
- Chou EH, Dickman E, Tsou PY et al., Ultrasonography for confirmation of endotracheal tube placement: A systematic review and meta-analysis.
- Resuscitation. 2015;90:97-103.
Gottlieb M and Bailitz J. Can transtracheal ultrasonography be used to verify endotracheal tube placement? Ann Emerg Med. 2015, Article in Press.