The ratio of a person's height to the sternomental distance (RHSMD) can help to identify a patient who may have a difficult endotracheal intubation.


(1) sternomental distance in cm (distance from sternal notch to the mental prominence with the head fully extended and the mouth closed)

(2) height in cm


ratio of height to sternomental distance =

= (height) / (sternomental distance)



• The normal ratio is > 12.5. It is important to have the head fully extended.

• The value is about twice the ratio of the height to thyromental distance (RHTMD).

• A ratio <= 12.5 is associated with difficult intubation.



• The sensitivity is somewhat low but the specificity is high. The RHTMD has better metrics.

• The accuracy is 87% (Amruthraju et al).

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