CO2 Absorber Change Protocol: Manual Mode Not Required
You do not need to set your anesthesia machine to manual mode before changing the CO2 absorber mid-case; instead, increase fresh gas flow to 5-10 L/min and fully open the APL valve to create a semi-closed system that bypasses CO2 absorption temporarily. 1, 2
Pre-Change Preparation Steps
The critical safety measure is converting from a closed to a semi-closed system, not switching ventilation modes:
- Immediately increase fresh gas flow to 5-10 L/min before beginning the absorber change to prevent CO2 rebreathing during the brief period when the absorber is disconnected or non-functional 1, 2
- Fully open the APL valve to allow excess gas and CO2 to escape through the scavenging system, which is essential to prevent dangerous pressure buildup in the breathing circuit 1, 2
- Verify the scavenging system is switched on and functioning properly before increasing fresh gas flow to prevent operating room pollution 1, 3
- Maintain continuous capnography monitoring throughout the absorber change to watch for rising ETCO2 values that would indicate inadequate CO2 removal 1
Why Manual Mode Is Not Necessary
Modern anesthesia machines with turbine ventilation can maintain mechanical ventilation during absorber changes when proper fresh gas flow is established. The high fresh gas flow creates a semi-closed system where CO2 is washed out through the APL valve rather than absorbed, allowing continued mechanical ventilation 2, 3.
The key is adequate fresh gas flow, not the ventilation mode. Higher flows of 10 L/min provide the safest margin, particularly if the change takes longer than anticipated 1.
Step-by-Step Absorber Replacement
- Set oxygen flow to at least 5 L/min, with higher flows for larger patients or increased metabolic demand 2
- Monitor ETCO2 closely during the change—it should stabilize or decrease with adequate fresh gas flow 2
- Work quickly but carefully to minimize the time the system is open 2
- Never attempt to refill a canister mid-case; only use pre-filled, sealed canisters 2
Post-Replacement Verification
After installing the new absorber, system integrity must be confirmed:
- Perform a pressure leak test by occluding the patient-end and compressing the reservoir bag to 20-60 cmH2O to verify system integrity 4, 1
- Check all connections, ensuring the canister housing, breathing circuit connections, and APL valve are properly secured 2
- Verify unidirectional valve function, confirming inspiratory and expiratory valves are moving freely 2
- Gradually reduce fresh gas flow back to the desired maintenance level once the new absorber is confirmed functional and all connections are secure 1
Critical Pitfalls to Avoid
- Failing to increase fresh gas flow before starting the change leads to CO2 rebreathing and potential hypercarbia 1
- Forgetting to open the APL valve when increasing fresh gas flow causes dangerous pressure buildup that can compromise ventilation 1, 3
- Not verifying the new absorber color before installation may result in installing an exhausted canister 1
- Occult leaks in replacement absorbers have been reported and can render manual ventilation impossible—always check the new absorber before installation 5, 6
Backup Considerations
- Keep a self-inflating bag-valve-mask immediately available in case of circuit failure during the change 2
- Have a backup breathing circuit with fresh CO2 absorbent assembled and tested for infectious cases or if complications arise 2
- Communicate with the surgical team about the equipment maintenance and potential need to briefly adjust ventilation 2
Modern circle systems can safely operate at flows as low as 1 L/min once the absorber is functioning properly and all connections are verified 1.