Identifying the cricothyroid membrane

Learn how to find the cricothyroid membrane using ultrasound, in preparation for a surgical airway.

David Mackenzie MDCM FRCPC FACEP
David Mackenzie MDCM FRCPC FACEP
5th Jul 2018 • 3m read

Cricothyrotomy is one of the most difficult and stressful procedures that you might ever have to perform! The traditional approach of using landmarks to identify the cricothyroid membrane is often inadequate and can potentially damage the blood vessels of the larynx or the vocal cords. In this video, from our POCUS Masterclass, you'll learn how to find the cricothyroid membrane using ultrasound so that you can manage airway emergencies with greater safety and confidence.

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Video Transcript

[00:00:00] Why use ultrasound to locate the cricothyroid membrane? Cricothyrotomy is one of the most difficult and stressful procedures you might ever have to perform. The traditional approach of using landmarks to identify the cricothyroid membrane is often inadequate and can lead to damage of blood vessels of the larynx or the vocal cords. Ultrasound can help you locate the cricothyroid membrane. If you anticipate a difficult airway with a possible need for a surgical airway and you have the time

[00:00:30] to use ultrasound, it will help you to perform a cricothyrotomy successfully. You may not be able to use ultrasound if it's truly a crash situation, but if you have the time to prepare for a double setup, this will help you and your patient tremendously. It will decrease the risk of injuries and increase the chance of success. Let's review the anatomy. The cricothyroid membrane is inferior to the thyroid cartilage and superior to the cricoid cartilage. It's bounded by the cricothyroid muscle. It's small,

[00:01:00] typically 1 to 2 cm in length. The blue circle would be your target if you're performing a cricothyrotomy. Anatomical factors such as obesity, prior surgery, radiation or injury can make identifying the cricothyroid membrane more difficult. This is where ultrasound comes in. It can make the localization so much easier. We're going to choose a linear, high-frequency transducer to ensure you have excellent resolution, as the membrane is a superficial structure. To obtain an image of the

[00:01:30] cricothyroid membrane, place your transducer in a long-axis orientation, in the middle of the neck, with the indicator pointing towards the patient's head. You are placing the transducer between the thyroid and cricoid cartilage, right where you think you would find the cricothyroid membrane. It's important to keep your hand still and in a vertical plane. Here's what you would expect to see on ultrasound. The first thing to look for is the hyperechoic line, that shows the air-mucosal interface. Then look for the hyperechoic rings of the trachea,

[00:02:00] that are immediately superficial to the interface. Track these rings towards the head until they stop. The last cartilage that you'll see will look bigger and it's the cricoid cartilage. Then there's a gap and if you look towards the head, you'll see the thyroid cartilage. In between the thyroid cartilage and the cricoid cartilage sits the cricothyroid membrane. That's your target. That's where you'll be performing the cricothyrotomy. Let's look at the airway anatomy

[00:02:30] again to make sure you've got it. First, let's look for that hyperechoic air mucosal interface, which we see here. Immediately above it, you see some hyperechoic tracheal rings. Here's one here. As we follow these towards the head, we see a larger one that's the last in the row, then we have a gap. This is the cricoid cartilage. As we move further towards the head, we can identify the thyroid cartilage here. So, in between them lies the

[00:03:00] cricothyroid membrane. Once you've identified the membrane, use a marking pen to indicate the location on the neck. If you do need to make an incision for a cricothyrotomy, you know exactly where to cut to maximize success. You can proceed with your airway plan. Confident that if you do need to perform a surgical airway, you'll know exactly where to make the cut. Knowing the location of the cricothyroid membrane will make the situation less stressful for you and optimize the care for your patient.

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