Understanding Anesthesiology - The Global Regional Anesthesia ...

CO2 (carbon dioxide) absorber
The CO2 absorber is a component of the circle anesthetic circuit. Before the exhaled gas is recirculated
back to the patient, it passes through the CO2 absorber where CO2 is scrubbed
out. By removing the waste gas (CO2), the CO2 absorber allows “rebreathing” or recirculation
of exhaled gases. Through rebreathing, air, oxygen, nitrous oxide and the volatile anesthetics
can be used more economically.
The CO2 absorber contains a hydroxide called soda lime-Ca(OH)2.
The reaction takes place over three steps and can be described as follows:
CO2 + H2O → aqueous CO2
aqueous CO2+ NaOH → NaHCO3
NaHCO3 + Ca(OH)2 → CaCO3 + H2O + NaOH
NaOH is a catalyst and is recycled to step 2.
Each mole of CO2 (44g) reacted produces one mole of water (18g).
The overall reaction, which is a heat-producing one that requires the presence of water, is:
CO2 + Ca(OH)2 → CaCO3 + H2O
The sodalime granules are manufactured with a chemical indicator such that as the soda
lime becomes exhausted, it changes colour.
Related Glossary Terms
Anesthetic circuit, Capnograph, Circle circuit
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Chapter 2 - Anesthetic Equipment and Monitoring
Chapter 6 - Inhaled Agents