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CO from CO2 absorber

Issue: Desiccated (or dry) CO2 absorbers such as soda lime and Baralyme can degrade inhaled anesthetics to carbon monoxide, and my produce carboxyhemoglobin concentrations in excess of 30%.

Mechanism: These CO2 absorbers contain strong bases (sodium hydroxide and potassium hydroxide) that can extract labile protons from anesthetic molecules, resulting in the production of CO. (There are new CO2 absorbers that do not contain KOH or NaOH, such as Amsorb. These do not react with inhaled agents to produce CO, but they are fairly expensive).

Incidence: The incidence of CO exposure is 0.46% for the first case of the day (2.9% in non-OR settings) and overall incidence is 0.26%.

Factors that increase the production of CO and carboxyhemoglobin:

1. Inhaled anesthetic used: des>/=enflurane>iso>>halothane=sevo

2. Absorbent dryness

3. Type of absorbent (Baralyme>soda lime)

4. Increased temperature

5. Low fresh gas flow

6. Increasing anesthetic concentration

7. Size of patient compared to amount of absorbent (i.e. more absorbent and hence more CO exposure per unit of patient mass

Interventions to reduce the risk of CO exposure:

1. Educate personnel on risk of CO production

2. Turn off anesthesia machine at the end of the day (leaving the anesthesia machine on at high oxygen flow rates overnight can dry the soda lyme)

3. Change CO2 absorber if you find gas flowing in machine

4. Rehydrate desiccated absorbers

5. Use absorbers that do not contain strong bases


  1. M J Coppens, L F M Versichelen, G Rolly, E P Mortier, M M R F Struys The mechanisms of carbon monoxide production by inhalational agents. Anaesthesia: 2006, 61(5);462-8 PubMed Link