Rationale
- Pulmonary aspiration at induction is rare but carries high morbidity and mortality
- Aspiration was the single commonest cause of airway-related death in NAP4, and several deaths followed omission of RSI in high-risk patients
- Cricoid pressure (CP) aims to prevent passive regurgitation between loss of consciousness and cuff inflation, as popularised by Sellick (1961)
- The case for CP rests on a plausible mechanism, functional occlusion studies and the scale of harm when aspiration happens (although none of it is based on evidence from a trial)
Mechanism
- Original concept: the oesophagus is compressed between the cricoid ring and the C6 vertebral body
- MRI work (Rice 2009) shows CP compresses the post-cricoid hypopharynx, which moves with the cricoid as one unit:
- Lateral position of the oesophagus may therefore not matter
- The target has shifted from oesophagus to hypopharynx meaning studies refuting oesophageal occlusion do not necessarily refute hypopharyngeal occlusion
- Cadaver work: 20 N held back 25 mmHg and 30 N held back 40 mmHg of oesophageal pressure; gastric pressure under anaesthesia is usually below 25 mmHg
| Year | Study | What it showed |
| 1961 | Sellick | 26 high-risk patients; no regurgitation with CP, regurgitation in 3 on release. Uncontrolled |
| 1992 | Vanner and Pryle (cadavers) | 20-30 N holds back oesophageal pressures above typical gastric pressures |
| 1997 | Vanner et al. | At 30 N, laryngeal view unchanged or improved; harm came from excessive force |
| 2009 | Rice et al. (MRI) | CP compresses the post-cricoid hypopharynx whatever the position of the oesophagus |
| 2011 | NAP4 | Aspiration caused over half of airway deaths; omitting RSI caused harm; no major complication attributed to CP |
| 2014 | Zeidan et al. | 30 N stopped a nasogastric tube passing in anaesthetised patients: functional occlusion |
| 2021 | Hung et al. (meta-analysis) | CP did not reduce first-attempt or overall intubation success with videolaryngoscopy |
Key arguments
- Mechanical occlusion is real when force is right: 30 N prevents passage of a nasogastric tube in anaesthetised, paralysed patients
- Limits gastric insufflation during mask ventilation; relevant now that gentle mask ventilation during RSI is accepted practice
- Correct technique reduces the harms:
- At 30 N the laryngoscopic view is usually unchanged or improved
- Videolaryngoscopy lets the team see and correct poor placement
- With videolaryngoscopy, CP does not reduce first-attempt success, although tube advancement may be harder
- Absence of evidence is not evidence of absence:
- A trial powered for clinically important aspiration would need tens of thousands of high-risk patients
- IRIS could not exclude more than a doubling of aspiration risk without CP (upper 95% confidence limit for relative risk 2.38)
- Medicolegal weight: UK courts (M v East Hertfordshire HA, 1991) and US closed claims data have treated omission as the riskier position for the clinician