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Quantification of the effect of body mass index on cricothyroid membrane depth: a cross-sectional analysis of clinical CT images
  1. Sadia Ghaffar1,
  2. Tom Nicholas Blankenstein2,3,
  3. Dilip Patel4,
  4. Catherine Theodosiou1,
  5. David Griffith5
  1. 1 Department of Anaesthesia, Edinburgh Royal Infirmary, Edinburgh, UK
  2. 2 HQ Army Medical Directorate, Army Medical Services, Camberley, Surrey, UK
  3. 3 Clinical Radiology, South- East Scotland Deanery, Edinburgh, UK
  4. 4 Department of Radiology, Royal Infirmary of Edinburgh, Edinburgh, UK
  5. 5 Division of Medical and Radiological Sciences, University of Edinburgh, Edinburgh, UK
  1. Correspondence to Dr Sadia Ghaffar, Department of Anaesthesia, Edinburgh Royal Infirmary, Edinburgh EH16 4SA, UK; sadia_ghaffar{at}


Objectives The recommended front of neck access procedure in can’t intubate, can’t oxygenate scenarios relies on palpation of the cricothyroid membrane (CTM), or dissection of the neck down to the larynx if CTM is impalpable. CTM palpation is particularly challenging in obese patients, most likely due to an increased distance between the skin and the CTM (CTM depth). The aims of this study were to measure the CTM depth in a representative clinical sample, and to quantify the relationship between body mass index (BMI) and CTM depth.

Methods This is a retrospective analysis of 355 clinical CT scans performed at a teaching hospital over an 8-month period. CTM depth was measured by two radiologists, and mean CTM depth calculated. Age, gender, height and weight were recorded, and BMI calculated. Linear relationships between patient characteristics and CTM depth were assessed in order to derive a predictive equation for calculating CTM depth. The variables included for this model were those with a strong association with CTM depth, that is, a p value of 0.10 or less.

Results Mean CTM depth was 8.12 mm (IQR 6.36–11.70). There was no association between CTM depth and sex (β −0.33, 95% CI −1.33 to 0.68, p=0.53), height (cm) (β 0.01, 95% CI −0.05 to 0.06, p=0.79) or age (years) (β −0.01, 95% CI 0.10 to 0.15, p=0.62). Increasing weight (kg) (β 0.12, 95% CI 0.10 to 0.15, p<0.001) and BMI (kg/m3) (β 0.52, 95% CI 0.44 to 0.60, p<0.001) were strongly associated with CTM depth. Predicted CTM depth increased from 6.4 mm (95% CI 4.9 to 8.1) at a BMI of 20 kg/m2 to 16.8 (95% CI 13.7 to 20.1) at BMI 40 kg/m2.

Conclusion CTM depth was strongly associated with BMI in a retrospective analysis of patients having clinical CT scans.

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  • anaesthesia

Data availability statement

All data relevant to the study are included in the article or uploaded as online supplemental information.

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Data availability statement

All data relevant to the study are included in the article or uploaded as online supplemental information.

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  • Handling editor Ellen J Weber

  • Twitter @Griffith_DM

  • Contributors All authors have contributed to the production of this work. SG—idea, methods, patient selection, extraction of patient data, writing of manuscript—including statistics, tables and figures. Revision and review of manuscript. TNM and DP—measurement of CTM depth on CT scans. Review of final manuscript. CT: ideas, help with methods and patient selection, review of final manuscript. DG: statistics, manuscript—including statistics, tables and figures. Revisions and review of manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; internally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.