• Anastasia Aslani, Su-Cheen Ng, Michael Hurley, Kevin F McCarthy, Michelle McNicholas, and Conan Liam McCaul.
• Department of Anaesthesia, The Rotunda Hospital, Dublin 1, Ireland.
• Anesth. Analg.. 2012 May 1;114(5):987-92.

BackgroundThe cricothyroid membrane (CTM) is the recommended site of access to the airway during cricothyroidotomy to provide emergency oxygenation. Despite the apparent simplicity of the technique, this rescue maneuver frequently fails to achieve its goals and complications are numerous. The reasons for this failure are unclear. We sought to determine the ability of physicians to correctly identify the CTM in female patients.MethodsUsing fluorescent "invisible" ink, the physician was asked to mark the CTM with the patient in the supine neutral position and then with the head extended. The actual level was identified using ultrasound and the distance between the actual and estimated margin of the CTM was measured. A correct estimation was defined as a mark made between the upper and lower limits of the membrane and within 5 mm of midline. Participants were also asked to assess the ease of CTM palpation using a 10-cm visual analog scoring (VAS) scale.ResultsFifty-six patients participated of whom 15 were obese. In the supine neutral neck position, the CTM was identified in 10/41 vs 0/15 (P = 0.048) in nonobese versus obese, respectively. Of the 46 incorrectly identified CTMs in this position, 24 were above (maximum 3 cm) and 22 below (maximum 3 cm) the actual level. Similar results were observed when the patients were placed with the neck in the extended position; the CTM was identified correctly in 12/41 vs 1/15 nonobese and obese patients, respectively. The range of values was also extensive; the estimation of the position of the membrane was as high as 2.5 cm above and 4 cm below the actual level, and up to 1.6 cm laterally. Participating doctors found palpation of the CTM subjectively more difficult in the obese than nonobese groups; VAS score for palpation difficulty was 5.25 ± 2.5 vs 3.3 ± 2.5, respectively, P = 0.005. Using multiple linear regression, VAS scores for palpation correlated negatively with increased patient height (P < 0.001) and greater thyromental distance (P = 0.006), and correlated positively with increased sternomental distance (P = 0.011) and neck circumference (P = 0.001).ConclusionsMisidentification of the CTM in female patients is common and its localization is less precise in those who are obese. This has implications for the likely success of invasive airway access via the CTM.

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