| Sellick BA, 1961, UK | 26 high risk anaesthesia cases in which cricoid pressure was applied | Observational study | Incidence of reflux of gastric/oesophageal contents when cricoid pressure released post-intubation of trachea | In 3 out of 26 cases release of cricoid pressure was followed by immediate reflux of gastric contents into pharynx | Observational study in few patients. Study conducted in 1961 using anaesthetic techniques available at that time |
| Brimacombe JR and Berry AM, 1997, Canada | Clinical and cadaver studies | Meta-analysis | Evidence of aspiration | No high quality studies proving that cricoid pressure is beneficial in preventing aspiration | No search strategy given |
| Some studies report acid aspiration despite cricoid pressure | No inclusion criteria |
| Airway patency | Some reports of cricoid pressure impeding airway patency | No assessment of quality of studies |
| Upper oesophageal sphincter pressure | Some evidence suggesting cricoid pressure increases upper oesophageal sphincter pressure | Various outcome measures used |
| Gastric insufflation with BVM | Some evidence that cricoid pressure reduces gastric insufflation during BVM | No definitions for aspiration pneumonia given |
| Airway/soft tissue injury | Case reports of cricoid injury/soft tissue injury | |
| Smith KJ et al, 2003, Canada | 22 healthy volunteers | Observational study. MRI scans of necks were taken with and without the application of cricoid pressure | Oesophageal displacement laterally relative to the cricoid without cricoid pressure | 52.6% of cases | Healthy awake volunteers were used, not paralysed patients undergoing RSI. Findings may be influenced by muscle tone and the swallowing reflex |
| Oesophageal displacement laterally relative to the cricoid with cricoid pressure | 90.5% of cases |
| Unopposed oesophagus without cricoid pressure. | 47.4% of cases |
| Unopposed oesophagus with cricoid pressure. | 71.4% of cases |
| Lateral laryngeal displacement | 66.7% of cases |
| Airway compression | 81% of cases |