Is it time to stop using cricoid pressure?

“We can’t act under pressure from anybody when we think that pressure will force an injustice” – José Sulaimán

Background

Cricoid pressure was first suggested in 1961 by Sellick to combat regurgitation during head down positioning for intubation.
- Sellick described “tonsillectomy position” head extension to straighten oesophagus, with pressure on cricoid cartilage to occlude oesophagus against C6 vertebral body
- “Moderate” pressure whilst patient awake, increased to “firm” once asleep
There is no level 1 evidence for efficacy, wide international variation in adoption
Cricoid pressure remains standard of care during RSI according to UK guidelines e.g. DAS
There are some concerns that cricoid pressure may worsen laryngoscopic view.

Aims

The IRIS trial aimed to demonstrate that a sham procedure mimicking cricoid pressure was not inferior to the real thing in preventing pulmonary aspiration

Methods

Sham vs real cricoid pressure in patients presenting to theatre for emergency surgery under GA, with risk factors for aspiration
Ten academic hospitals in France, 1:1 randomisation in blocks of 6 to cricoid or sham
A total of 3472 patients were recruited; 1729 patients in Sellick group, 1730 in sham group
Intubators & patients blinded to allocation
Exclusions: pregnancy, pneumonia, “consciousness disorder”

Statistical design: Non-inferiority RCT

Authors decided that at worst, sham pressure could have 1.5x higher risk of aspiration and still be deemed not inferior
This meant that upper limit of 95% confidence interval needed to be ≤1.5
1:1 randomisation in blocks of 6
Powered for 2.8% incidence of aspiration (based on Martin et al, Anaesthesiology 2011)

Results

Primary outcome: pulmonary aspiration, per-protocol analysis
- 10/1729 cricoid pressure patients aspirated (0.6%)
- 9/1730 sham pressure patients aspirated (0.5%)
- RR 0.90 (95% CI 0.39-2.00)
Secondary outcomes:
- Intubation time (seconds, IQR): 27(19-40) cricoid vs 23(15-37) sham
- Incidence of CL view 3 or 4: cricoid 8%, sham 4%

Discussion

Based on pre-specified threshold, authors conclude sham pressure is not “non-inferior” to cricoid pressure
They failed to show sham pressure is no worse than cricoid pressure, according to their own definition
The overall incidence of aspiration significantly lower than expected
Although a secondary outcome, the IRIS trial reports that cricoid worsens laryngoscopic view
Strengths:
- Standardised anaesthetic technique and application of cricoid by trained operators
- Randomisation & blinding techniques
- No significant between group differences at baseline
Flaws:
- There was a large overestimation of the risk of aspiration risk which meant that the study was underpowered
- Theatients at highest risk of desaturation, difficult airway, aspiration were excluded
  - Pregnancy, ICU/ED, cardiac arrest, low GCS, pneumonia
- Suxamethonium was used rather than rocuronium which means the results are possibly less applicable in some centres

Should this trial change our practice?

This trial does not inform most of the highest risk situations in which cricoid is employed
IRIS trial does not seriously undermine either of the two camps: cricoid is dangerous (worse view, ineffective) or necessary (not dangerous, might prevent aspiration in higher risk patients, can always be removed)
Cricoid pressure remains recommended by DAS and used routinely in UK obstetric practice (Desai IJOA 2018)

Summary by Dr Charles McFadyen

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