| Angle | dropping | p-value | ||
| Yes | None | Total | ||
| Tracheal intubation |
|
|
| <0.001*: |
| 0˚ | 0 | 360 | 360 |
|
| 20˚ | 1 | 359 | 360 |
|
| 40˚ | 6 | 354 | 360 |
|
| 60˚ | 12 | 348 | 360 |
|
| 90˚ | 49 | 311 | 360 |
|
| Tracheotomy 90˚ | 59 | 301 | 360 | 0.15† |