| Benumof JL, 1996, USA | 181 elective patients undergoing GA.Back plus cephalad pressure was compared with standard view | Observational study | Improvement of laryngoscopic view | All views improved | |
| | | Number of improved views in grade 3 group | All views improved | |
| Takahata O, 1997, Japan | 630 patients undergoing routine surgery.BURP was compared with back pressure on the larynx | Observational study | Number of improved views in grade 3 group | 357 grade 1 views, 261 grade 2 views,12 grade 3 views, 0 grade 4 views. 9 patients with an initial grade 3 Cormack view improved to grade 2 after simple back pressure. | Comparison was with back pressure on thyroid cartiladge rather than on cricoid.Very small number of initial grade 3, and no grade 4 views. |
| | | Number of improved views in grade 3 group | All patients with an initial grade 3 Cormack score improved to grade 2 after BURP. | |
| | | Number of grade 2 views that improved (to grade 1 or an improved grade 2) | 176/261 after back pressure alone. 42/85 further improved with BURP | |
| Vanner RG, 1997, UK | 55 elective female patients standard view v simple cricoid v cricoid plus upward pressure | Observational study | Number of improved views with upward pressure v simple cricoid alone | Better with upward pressure | Only female patients |