The ratio of the neck circumference to thyromental distance is a bedside measure that can help to identify a patient likely to have a difficult laryngoscopy or endotracheal intubation.
Parameters:
(1) neck circumference at the level of the cricoid cartilage in cm
(2) thyromental distance in cm
ratio of neck circumference to thyromental distance =
= (neck circumference) / (thyromental distance)
Interpretation:
• A ratio > 5.6 is associated with difficult laryngoscopy.
• Neck circumference for a given height increases with obesity and correlates with obstructive sleep apnea.
Performance:
• The area under the ROC cuve is 0.69.
• The sensitivity was 0.7 and the specificity was 0.7.
• The negative predictive value was 96% but positive predictive value was only 17%.
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