Accurately identifying the cricothyroid membrane is foundational for front-of-neck rescue of airway misadventure. Yet the very patients who are at risk of a cannot intubate, cannot oxygenate scenario (eg. obese, neck pathology) are also likely to make identifying the cricothyroid membrane (CTM) difficult.

Naveed and co. compared the accuracy of CTM palpation to ultrasound in a single-blinded randomized trial of 223 patients, with poorly defined landmarks, undergoing CT neck.

The ultrasound group showed a 10-time greater success in identifying the CTM (correct within 5 mm of actual; 81% vs 8%), along with a 5-times smaller mean distance from actual to estimated, than did the palpation group.

So what's the take home?

Given the wide-availability of ultrasound and it's acceptability to patients, any pre-induction marking of the CTM in an anticipated difficult airway should employ neck ultrasound in all but the most obviously-palpable necks.

In an emergent CICO situation, neck ultrasound likely has utility, though at the potential cost of procedural complexity and delay.

summary

• Naveed Siddiqui, Eugene Yu, Sherif Boulis, and Kong Eric You-Ten.
• From the Department of Anesthesia and Acute Pain Service (N.S.) the Neuroimaging Faculty, Princess Margaret Hospital (E.Y.) the Departments of Anesthesia (S.B., K.E.Y.-T.) Pain Management (K.E.Y.-T.), Mount Sinai Hospital, University of Toronto, Canada.
• Anesthesiology. 2018 Dec 1; 129 (6): 1132-1139.

What We Already Know About This TopicWHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Success of a cricothyrotomy is dependent on accurate identification of the cricothyroid membrane. The objective of this study was to compare the accuracy of ultrasonography versus external palpation in localizing the cricothyroid membrane.MethodsIn total, 223 subjects with abnormal neck anatomy who were scheduled for neck computed-tomography scan at University Health Network hospitals in Toronto, Canada, were randomized into two groups: external palpation and ultrasound. The localization points of the cricothyroid membrane determined by ultrasonography or external palpation were compared to the reference midpoint (computed-tomography point) of the cricothyroid membrane by a radiologist who was blinded to group allocation. Primary outcome was the accuracy in identification of the cricothyroid membrane, which was measured by digital ruler in millimeters from the computed-tomography point to the ultrasound point or external-palpation point. Success was defined as the proportion of accurate attempts within a 5-mm distance from the computed-tomography point to the ultrasound point or external-palpation point.ResultsThe percentage of accurate attempts was 10-fold greater in the ultrasound than external-palpation group (81% vs. 8%; 95% CI, 63.6 to 81.3%; P < 0.0001). The mean (SD) distance measured from the external-palpation to computed-tomography point was five-fold greater than the ultrasound to the computed-tomography point (16.6 ± 7.5 vs. 3.4 ± 3.3 mm; 95% CI, 11.67 to 14.70; P < 0.0001). Analysis demonstrated that the risk ratio of inaccurate localization of the cricothyroid membrane was 9.14-fold greater with the external palpation than with the ultrasound (P < 0.0001). There were no adverse events observed.ConclusionsIn subjects with poorly defined neck landmarks, ultrasonography is more accurate than external palpation in localizing the cricothyroid membrane.

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