Patient evaluation included cephalometric analysis of lateral radiographs with the head in neutral and extended (intubation) positions.
Parameters:
(1) thyrosternal distance in cm
(2) Mallampati class, from 1 to 4
(3) thyromental distance in cm
(4) neck circumference in cm
(5) depth of spinous process for C2 in mm (V13)
(6) angle A (V20) in degrees from the lateral radiograph with the head extended
where (see Figures 1 and 2):
• In the extended radiograph, angle A is from the triangle ABC (between lines AB and AC).
• A the most antero-inferior point of the upper incisor tooth
• C is the antero-inferior border of the 6th cervical vertebra.
• AB is the line along the occlusal surfaces of the maxillary teeth.
• B is on the anterior aspect of C1 at a point intersecting lines AB and BC.
L1 =
= (1.1003 * (thyrosternal distance in cm)) - (2.6076 * (Mallampati class)) + (0.9684 * (thyromental distance in cm)) - (0.3966 * (neck circumference in cm)) + 4.9504
L2 =
= (1.2422 * (thyrosternal distance in cm)) - (3.368 * (Mallampati class)) + (0.966 * (thyromental distance in cm)) - (0.3192 * (depth of spine C2 in mm)) + (0.176 * (angle A in degrees)) - 10.2717
Interpretation:
• A negative index (L1 or L2 < 0) indicates that difficulty will be encountered.
• L2 has a greater predictive ability and should be used if the results are discrepant.
NOTE: In Case 2 from the Appendix, the result reported is -0.9828. My calculation is -2.2145, both in the spreadsheet and by multiplying the numbers by hand.
