Final answer:
A thyromental distance of less than 3 fingers' breadth is a not a reassuring finding, suggesting a potentially difficult airway during endotracheal intubation.
Step-by-step explanation:
The measurement of thyromental distance that is not a reassuring finding is c) Less than 3 fingers' breadth. The thyromental distance is the straight line measurement from the thyroid notch to the front of the mentum (chin) with the head fully extended. In clinical practice, it provides an assessment of the adequacy of the space for the tongue during intubation, and it is typically measured in fingers' breadth or centimeters. A thyromental distance of less than 6 cm or less than 3 fingers' breadth may indicate a potentially difficult airway because it suggests there is less room to accommodate the tongue during endotracheal intubation. In contrast, a thyromental distance of greater than 9 cm or greater than 12 cm suggests a more favorable scenario for intubation because it indicates more space in the airway.