What is the proper procedure for changing a CO2 (carbon dioxide) absorber during an ongoing anesthesia case?

How to Change a CO2 Absorber During an Ongoing Anesthesia Case

When changing a CO2 absorber mid-case, temporarily switch to a non-rebreathing system or increase fresh gas flow to bypass CO2 absorption, perform the canister replacement quickly while maintaining ventilation through an alternative method, then verify system integrity before resuming normal operation.

Pre-Change Preparation

Before initiating the canister change, assess whether the replacement is truly urgent or can wait until the case concludes. The decision depends on:

• Color indicator change: Most modern absorbents change color when exhausted (typically white/pink to purple/blue) 1
• End-tidal CO2 trending upward: Rising ETCO2 despite stable ventilation parameters indicates absorbent failure 2
• Duration of case remaining: If less than 30 minutes remain and ETCO2 is stable, consider continuing with current canister 1

Step-by-Step Procedure

1. Convert to Semi-Closed or Non-Rebreathing System

Immediately increase fresh gas flow to 5-10 L/min and fully open the APL valve to create a semi-closed system that minimizes CO2 rebreathing 3. This bypasses the need for CO2 absorption temporarily while you perform the change 3.

• Set oxygen flow to at least 5 L/min (higher for larger patients or increased metabolic demand) 3
• Fully open the APL valve to allow excess gas and CO2 to escape through the scavenging system 3, 4
• Verify the scavenging system is functioning properly to prevent operating room pollution 3, 4
• Monitor ETCO2 closely—it should stabilize or decrease with adequate fresh gas flow 3

2. Perform the Canister Replacement

Work quickly but methodically to minimize time without CO2 absorption:

• Remove the exhausted canister: Unscrew or unlatch the canister housing according to your machine's design 1
• Inspect seals and connections: Check O-rings and gaskets for damage or debris before installing the new canister 1
• Install fresh absorbent: Ensure the new canister is properly seated and locked into position 1
• Verify no tilting: Keep the canister upright throughout—tilting can cause channeling and reduced absorption efficiency 1

Common pitfall: Failing to properly seat the canister creates bypass pathways where CO2-laden gas circumvents the absorbent, leading to hypercarbia despite a fresh canister 1.

3. System Integrity Verification

After installing the new canister, you must verify proper function before returning to low-flow anesthesia:

• Perform a leak test: Occlude the patient end of the circuit, squeeze the reservoir bag, and observe for pressure maintenance (20-60 cmH2O) 1
• Check all connections: Ensure the canister housing, breathing circuit connections, and APL valve are properly secured using "push and twist" technique 1
• Verify unidirectional valve function: Confirm inspiratory and expiratory valves are moving freely 1

If you cannot perform a complete leak test mid-case (patient cannot tolerate circuit disconnection), at minimum verify that:

• The canister housing is fully locked 1
• No visible gaps exist around the canister 1
• ETCO2 decreases appropriately when you reduce fresh gas flow 3

4. Return to Normal Operating Parameters

Once system integrity is confirmed:

• Gradually reduce fresh gas flow to your desired level (typically 0.5-2 L/min for low-flow anesthesia) 3
• Adjust APL valve to partially closed position appropriate for your ventilation mode 3, 4
• Monitor ETCO2 closely for 5-10 minutes to ensure it remains stable at normal levels 3
• Document the change including time, reason for change, and verification steps performed 1

Special Considerations

High-Risk Situations

For infectious cases (COVID-19 or other airborne pathogens): The Chinese Society of Anesthesiology recommends replacing CO2 absorbers between cases due to the large surface area that could harbor pathogens 1, 2. If mid-case replacement is necessary:

• Wear appropriate PPE including N95 respirator 1
• Treat the used canister as contaminated waste 1
• Minimize aerosolization by avoiding sudden disconnections 1

Alternative Approach: Backup Circuit

Some departments maintain a completely separate, pre-checked circle system that can be rapidly swapped:

• Keep a backup breathing circuit with fresh CO2 absorbent assembled and tested 1
• During a brief apneic period or hand ventilation, disconnect the old circuit and connect the new one 1
• This approach minimizes time at high fresh gas flows and ensures complete system integrity 1

Critical Safety Points

• Never attempt to refill a canister mid-case—only use pre-filled, sealed canisters 1
• Maintain continuous monitoring of ETCO2, SpO2, and airway pressures throughout the procedure 3
• Have backup ventilation ready: Keep a self-inflating bag-valve-mask immediately available in case of circuit failure 4
• Communicate with the surgical team: Inform them you're performing equipment maintenance and may need to briefly adjust ventilation 1

The entire procedure should take less than 2-3 minutes with practice, during which time the high fresh gas flow prevents CO2 accumulation and maintains adequate anesthesia delivery 3.