2 Machine Check & Safety Systems
Bailey Freeman, DNP, CRNA and Angela Mordecai
Quick Facts
- Anesthesia machine safety systems are critical for preventing hypoxia, gas delivery errors, and CO₂ rebreathing.
- Fail-safe valves and hypoxic guards limit delivery of non-oxygen gases if O₂ supply is interrupted.
- CO₂ absorbers are used in rebreathing systems to remove carbon dioxide from exhaled gases.
- Oxygen supply alarms notify the provider if pipeline or cylinder O₂ falls below minimum pressure.
- A thorough pre-use checklist helps detect equipment issues before anesthesia begins.
Procedure
Fail-Safe Systems
- Fail-Safe Valve: Limits or stops N₂O and other gases if O₂ pressure drops below ~30 psi.
- Hypoxic Guard: Prevents O₂ concentration from falling below ~25% in delivered gas mixtures.
CO₂ Absorber
- Contains soda lime or equivalent to chemically absorb CO₂.
- Should be replaced when color change is noted or after designated use time.
- Signs of exhaustion: rising ETCO₂, rebreathing, increased FiCO₂.
Oxygen Alarms
- Activate if oxygen supply pressure drops below ~30 psi.
- Must be audible and functional—test daily during startup checks.
- O₂ analyzer confirms inspired oxygen concentration in the patient circuit.
Pre-Use Checklist
- Verify electrical power and battery backup.
- Confirm pipeline and cylinder O₂ sources are connected and have adequate pressure.
- Check vaporizers: fill levels, locked, and not leaking.
- Test flowmeters and scavenging system.
- Perform leak test on the breathing circuit.
- Check function of manual and mechanical ventilation modes.
- Confirm audible O₂ low-pressure alarm functions.
- Inspect and reset monitors: O₂ analyzer, ETCO₂, pressure, volume.
Confirmation Steps
- Document that all machine safety and function checks were performed before the case.
- Ensure O₂ alarm and fail-safe are functioning using manual test methods.
- Replace CO₂ absorber if nearing expiration or color indicates exhaustion.
Documentation Requirements
- Daily machine check performed and signed off (electronic or paper record).
- Vaporizer agent and fill status confirmed.
- Alarm functionality verified and any issues reported or resolved.
Scope Guide
Strategies
- Incorporate the pre-use checklist into your daily routine before the first case.
- Review manufacturer-specific fail-safe and alarm settings for each machine model used.
Clinical Optimization
- Monitor FiO₂ and ETCO₂ continuously; they are early indicators of machine or absorber failure.
- Keep spare CO₂ absorbent canisters available for immediate replacement during long cases.
Pearls
- Do not rely solely on fail-safe valves—confirm inspired O₂ using a dedicated analyzer.
- Alarms must be loud enough to be heard over surgical noise—never silence without resolution.
- Performing a thorough machine check before each case prevents the vast majority of preventable errors.
References
- StatPearls. Anesthesia Machine Pre-use Check. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK554538/
- OpenAnesthesia. CO₂ Absorbers, Fail-Safe Devices, and O₂ Alarms. https://www.openanesthesia.org/
- How Equipment Works. Safety Systems in Anesthesia Machines. https://www.howequipmentworks.com/
