| Angle | dropping | p-value | ||
| Yes | None | Total | ||
| Tracheal intubation |
|
|
| <0.001*: |
| 0˚ | 3 | 477 | 480 |
|
| 20˚ | 10 | 470 | 480 |
|
| 40˚ | 16 | 464 | 480 |
|
| 60˚ | 24 | 456 | 480 |
|
| 90˚ | 48 | 432 | 480 |
|
| Tracheotomy 90˚ | 59 | 421 | 480 | 0.26† |