Thyromental Distance
Thyromental Distance
The thyromental distance (TMD) is defined as the distance from the chin (mentum) to the top of the notch of the thyroid cartilage with the head fully extended; it must be measured with a ruler for accuracy. The TMD gives an estimate of the mandibular space and helps in determining how readily the laryngeal axis will fall in line with the pharyngeal axis when the A-O joint is extended:
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A TMD measurement of 6.5 cm or greater with no other abnormalities indicates the likelihood of easy intubation.
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A TMD measurement of 6.0 to 6.5 cm indicates that alignment of the pharyngeal and laryngeal axes will be challenging and that difficulty with laryngoscopy may result. However, intubation is possible with the use of adjuncts such as an Eschmann introducer or an optical stylet.
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A TMD measurement of less than 6 cm indicates difficult laryngoscopy; specifically, intubation may be impossible.
TMD, in conjunction with other parameters such as the MP classification, has been used to predict DI.
