During anaesthesia with a circle system, the CO₂ absorbent changes from white to violet. However, EtCO₂ remains normal. The MOST likely explanation is:
- A The absorbent has been exhausted and must be changed immediately
- B The EtCO₂ monitor is malfunctioning; replace the sampling line
- C Colour change is a pH indicator response; some absorbents (e.g., Amsorb) temporarily reverse colour upon rest — functional adequacy must be confirmed by EtCO₂ trending ✓
- D CO₂ absorber is underutilised and should be bypassed to save cost
Explanation
Traditional soda lime absorbents use a pH indicator (ethyl violet in soda lime changes from white to violet when exhausted, due to carbonate formation altering pH). However, this colour change can reverse after the absorbent rests (regenerates partially). Some modern absorbents (Amsorb, Dragersorb) use different indicators. The definitive functional test is EtCO₂ — if it remains low and stable, the absorbent is still functional despite discolouration. Conversely, if EtCO₂ rises, the absorbent is exhausted and must be replaced immediately. Clinical vigilance requires monitoring both the indicator and ETCO₂.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.