Verifying Cricoid Pressure Using a Syringe
Use a 50 mL syringe as an immediate training and verification tool before applying cricoid pressure by depressing the plunger to the appropriate force level: 10 N (1 kg) for awake patients and 30 N (3 kg) after loss of consciousness.
How the Syringe Method Works
The 50 mL syringe provides a reliable, linear relationship between plunger depression and applied force in the 20-50 N range 1. This creates an inexpensive, practical training device that can be used immediately before clinical application to calibrate the assistant's force application 2.
Practical Application Steps:
For Training:
- Depress the plunger of a 50 mL syringe to practice applying the correct force
- 10 N (1 kg) = lighter pressure for awake patients
- 30 N (3 kg) = firmer pressure after induction
- Practice until you can consistently apply these forces
For Clinical Use:
- Use the syringe immediately before applying cricoid pressure on the patient 2
- This pre-application training significantly improves performance: only 19% of untrained staff apply satisfactory force versus 47% of those who use the syringe training aid immediately beforehand (P=0.03) 2
Critical Force Guidelines
Current guidelines specify 3, 4:
- Awake patient: 10 N (1 kg) initially
- After loss of consciousness: 30 N (3 kg)
- Head-up position: Can reduce to 20 N (2 kg) 3
Common Pitfalls to Avoid
Excessive force is the most common problem 3. Too much pressure (>20 N in awake patients) causes:
- Retching and potential aspiration
- Airway obstruction
- Impaired laryngoscopy and intubation
- Difficulty with facemask ventilation
Training decay occurs rapidly: Performance deteriorates after 1 week and is not maintained at 1 month 1. Therefore, use the 50 mL syringe training aid immediately before each clinical application rather than relying on periodic training sessions 2.
When to Modify or Release Cricoid Pressure
- Active vomiting occurs
- Airway difficulty is encountered (poor laryngoscopy view, difficult mask ventilation, or LMA placement issues)
- When releasing, do so under direct vision with suction available and be ready to reapply if regurgitation occurs
Reduce force if 4:
- It impedes laryngoscopy
- It causes airway obstruction
- Patient is in head-up position (reduce to 20 N)
Why This Matters for Patient Safety
Without proper training, only 30% of practitioners apply appropriate force at 20 N and 40% at 40 N 1. The syringe method provides immediate calibration, making cricoid pressure both more effective and reliable 2. NAP4 data showed that omission of cricoid pressure in appropriate cases led to patient harm or death from aspiration, while no cases of major complications from properly applied cricoid pressure were reported 3.