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The Speed of Sound

The Speed of Sound: Confirming ET Tube Placement with Ultrasound

Butts, Christine MD

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doi: 10.1097/01.EEM.0000437843.60753.1b
    Figure. I
    Figure. I:
    mage 1. This image is approximately at the level of the vocal chords. The ET tube is seen in the center of the image as the brightly echogenic horizontal line (white) with posterior shadowing (arrow). The thyroid cartilage can be seen on either side of the ET tube (arrowheads), confirming its placement within the trachea.
    Figure
    Figure
    Figure. I
    Figure. I:
    mage 2. The esophagus lies approximately within this area (arrowhead), although it is not visible in this image. If the ET tube is suspected to lie within the trachea, the curved hyperechoic structure will be seen in this area instead of within the trachea (arrow).
    Figure. I
    Figure. I:
    mage 3. The ribs can be seen on either side of the image as rounded structures with a hyperechoic (white) border with posterior shadowing (arrowheads). Deep to the ribs, the pleura can be seen as a hyperechoic horizontal line (arrow). Viewed in real time, it should be seen to slide back and forth with respiration. Watch a video showing the pleura in action in EMN?'s app for the iPad on Nov. 5 and on our website on Nov. 12.

    Confirming correct endotracheal (ET) tube placement should be a straightforward process in an ideal world. Direct visualization of the tube passing through the cords is considered the gold standard by most, and many physicians use this in conjunction with another confirmatory method to convince themselves that the tube is in the trachea and not the esophagus. We may not be able to visualize proper placement directly in some cases, however, and our other methods may not be as reassuring. Ultrasound offers two methods of assessing for proper ET tube placement, directly and indirectly.

    The direct method involves an assessment of the trachea with ultrasound for the presence of the ET tube. This technique should be performed with the high-frequency transducer for optimal resolution of the laryngeal anatomy. Palpation of the landmarks of the larynx, such as the thyroid cartilage may be helpful, but is not necessary because the position can be quickly assessed by ultrasound. Placing the transducer in the transverse plane (indicator pointing toward the patient's right) at approximately this level will allow the examiner to identify normal anatomy and to evaluate the position of the tube. The ET tube is immediately recognizable as a hyperechoic (white) curved structure with strong posterior shadowing. (Image 1.)

    The anterior surface is frequently seen to have two paired hyperechoic lines representing the inner and outer surface of the tube. This structure should be seen in the midline of the larynx within the trachea. The esophagus lies deep and to the patient's left of the larynx (on the right side of the screen) and is typically not seen. Esophageal intubations can be identified by the presence of the characteristic ET tube at the bottom right of the screen instead of within the more anterior and midline trachea. (Image 2.)

    A more indirect method to assess proper placement of the ET tube is to assess the pleura for the presence of the slide sign. The pleura are easily identified from the anterior chest wall utilizing the high-frequency transducer. The transducer should be placed just inferior to the clavicle in the mid-clavicular line. Pointing the indicator toward the patient's head will produce an image that is easy to interpret. Once the skin, soft tissue, and ribs have been identified, the pleura will be seen as a hyperechoic (white) line running just deep to the rib. (Image 3.)

    The pleura should seem to “slide” back and forth when the lung is being ventilated. (See image 3 for information about a video demonstrating this finding.) Once sliding is confirmed to one side, the other side should be evaluated as well. The absence of sliding on one side may indicate a right main stem intubation, but a pneumothorax should also be considered because this can cause lack of sliding as well. Lack of sliding on either side should prompt the EP to consider misplacement of the ET tube.

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