How should you prepare the anesthesia machine before changing out a CO2 (carbon dioxide) absorber in the middle of a case?

Preparing the Anesthesia Machine Before Changing the CO2 Absorber Mid-Case

When changing a CO2 absorber during an active case, you must temporarily convert from a closed or low-flow system to a semi-closed system by increasing fresh gas flow to 3-10 L/min and ensuring the APL valve is partially open to prevent dangerous pressure buildup and maintain adequate ventilation. 1

Step-by-Step Preparation Protocol

1. Increase Fresh Gas Flow

• Immediately increase FGF to at least 3 L/min, preferably 5-10 L/min before beginning the absorber change 1
• This prevents rebreathing of CO2 during the brief period when the absorber is disconnected or non-functional 2
• Higher flows (10 L/min) provide the safest margin, particularly if the change takes longer than anticipated 3

2. Open the APL Valve

• Ensure the APL valve is partially open to allow excess gas to escape through the scavenging system 1
• Verify the valve can be fully opened and is functioning properly by squeezing the reservoir bag 3, 1
• This is critical—forgetting to open the APL valve when increasing FGF can cause dangerous pressure buildup in the breathing circuit 1

3. Verify Scavenging System Function

• Confirm the scavenging system is switched on and functioning before increasing FGF 1
• Check that tubing is properly attached to the exhaust port 1
• Inadequate scavenging with high FGF will lead to operating room pollution 1

4. Monitor Ventilation Continuously

• Maintain continuous capnography monitoring throughout the absorber change 4
• Watch for rising ETCO2 values that would indicate inadequate CO2 removal 4
• If ETCO2 rises rapidly despite increased minute ventilation, consider equipment malfunction or other pathology 4

During the Absorber Change

Maintain Adequate Ventilation

• Keep the patient ventilated with the increased FGF throughout the change 1
• The high flow compensates for the temporary loss of CO2 absorption capacity 2
• Do not disconnect the patient from the circuit if possible; work quickly to minimize any interruption 3

Work Efficiently

• Have the replacement absorber ready before starting 3
• Inspect the new absorber for proper color and adequate supply before installation 3, 1
• Ensure all connections are secure using the "push and twist" technique 3, 1

After Absorber Replacement

Verify System Integrity

• Perform a pressure leak test by occluding the patient-end and compressing the reservoir bag to 20-60 cmH2O 3
• Check all connections within the breathing system are secured 3, 1
• Verify no leaks or obstructions exist in the circuit 3

Return to Normal Flow Settings

• Once the new absorber is confirmed functional and all connections are secure, you may gradually reduce FGF back to your desired maintenance level 1
• Modern circle systems can safely operate at flows as low as 1 L/min once the absorber is functioning properly 3

Critical Pitfalls to Avoid

Common Errors

• Failing to increase FGF before starting the change leads to CO2 rebreathing and potential hypercarbia 1, 2
• Forgetting to open the APL valve when increasing FGF causes dangerous pressure buildup 1
• Inadequate scavenging with high flows pollutes the operating room environment 1
• Not verifying the new absorber color before installation may result in installing an exhausted canister 3, 1

Special Considerations for Modern Machines

• Newer anesthesia machines with smaller internal volumes and decoupling systems may require different preparation times 5
• Some machines automatically test system integrity, but manual verification is still recommended 3
• Never tilt the absorber canister during replacement, as this can cause channeling and reduced efficiency 3