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Image Acquisition using Portable Sonography for Emergency Airway Management
Chapters
Summary September 28th, 2022
Point of care ultrasound (POCUS) is increasingly being utilized in airway management. Presented here are some clinical utilities of POCUS, including differentiating endotracheal and esophageal intubation, identification of the cricothyroid membrane in the event a surgical airway is required, and measuring anterior neck soft tissue to predict difficult airway management.
Transcript
The utilization of airway POCUS has several indications in emergency or difficult airway management. In this video we will review some of these indications and how to acquire the ultrasound images necessary to be effective. The main advantage of utilization of airway POCUS is it is a rapid, easily accessible, and non-invasive imaging modality that can be used in high acuity clinical situations.
Although these protocols can be learned relatively quickly, I suggest that you practice them in a non-emergent situation in order to become comfortable and efficient. This is Dr.Erica Chemtob, a resident in our department demonstrating the procedure. Begin by preparing a high-frequency, linear ultrasound probe by placing a single layer of ultrasound gel on the probe transducer.
Select the linear probe from the transducer menu on the touch screen and specify MSK from the dropdown menu. Now, place the ultrasound in scanning mode by pushing the 2D button on the bottom left corner of the touch screen. Once the general anesthesia is induced, place the probe in the transverse position on the midline of the patient's anterior neck just cephalad to the suprasternal notch.
Identify the trachea midline and note the constricted esophagus just lateral to the trachea. For further anatomic confirmation, scan laterally to identify the carotid artery and internal jugular vein. Additionally, check that the hyperechoic posterior aspect of the trachea disappears due to the endotracheal tube, leaving a characteristic acoustic shadowing that is bullet-shaped.
To perform CTM identification, place the patient in the supine position with their neck extended. Prepare the ultrasound probe and place the probe to a depth of approximately 1.5 to 2 centimeters based on an average-sized patient, as the CTM is shallow in the neck. Then, perform the first method of CTM identification by placing a linear high-frequency probe in the sagittal plane of the patient's neck just caudal to the thyroid cartilage.
The thyroid cartilage appears as the superficial hypoechoic structure at the cranial side of the scan and casts an acoustic shadow. Now, locate the cricoid cartilage, which is in a caudal location and appears hypoechoic. Using the underlying air mucosal interface, identify the CTM lying between these two structures, which appears as a hyperechoic line running along the length of the trachea.
For further confirmation, scan caudally to locate the tracheal rings, which will appear as a hyperechoic string of beads. Alternatively, CTM can also be located by placing a linear high-frequency probe in the transverse plane at the level of the thyroid cartilage, which appears hyperechoic and casts an acoustic shadow of a black triangle with the tip being the most superficial. Scan in a caudal direction until the black triangle disappears as the thyroid cartilage ends and the CTM begins.
Identify this as the air mucosal interface that appears as a bright white line with reverberation effects. Keep scanning in a caudal direction until the CTM ends and the cricoid cartilage appears. The cricoid cartilage will appear as a hypoechoic band surrounding the trachea.
Once the cricoid is identified, the inferior border of the CTM is also located. To ensure that the proper anatomy has been identified, reverse these steps and scan in a cephalad direction;again, identifying the CTM and the thyroid cartilage. Once these landmarks have been identified, mark the CTM location on the patient.
To measure the skin to epiglottis distance, place the patient and prepare the probe and ultrasound as demonstrated earlier. Place a high frequency linear probe in the transverse position on the anterior neck at the level of the thyroid membrane. Identify the epiglottis, the hypoechoic structure midway between the hyoid bone and thyroid cartilage.
The laryngeal surface of the epiglottis forms a hyperechoic line representing the air mucosal interface. Tilt the probe in either direction if the anterior border of the epiglottis is not clearly defined. Note an echogenic pre-epiglottic space.
To measure the skin to epiglottis distance, freeze the image by touching the large freeze button at the bottom of the touch screen. Next, select the blue distance button on the right side of the screen. To measure the LPWT, place a curvilinear low-frequency probe in the coronal orientation below the mastoid process and in line with the carotid artery.
Then, use doppler flow to identify the carotid artery by pressing the C button on the bottom left of the screen. Using a finger on the touch screen, move the yellow box over the carotid vasculature and identify the carotid artery by noting the pulsatile vascular flow. To measure the LPWT, freeze the image as demonstrated earlier.
Place one cursor on the inferior border of the carotid artery and the second cursor on the anterior aspect of the airway. The LPWT will be displayed in the screen's gray box on the upper left side. Ultrasonographic measurements of the LPW showed that LPWT correlated with the severity of OSA based on the apnea-hypopnea index.
It is imperative to remember that in the emergency airway management scenario time is critical and may impact patient outcomes. It is essential that the provider who's performing airway ultrasound be skilled and proficient in image acquisition and interpretation in order to be beneficial in these scenarios.
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