While the color change is an indication of the hydrated state and remaining capacity, depletion of the absorbent should be determined by capnometry and the absorbent changed when FiCO2 has exceeded 0.5% volume or 5mmHg.
Desiccation of soda lime through contact with anhydrous gas or moisture loss through exposure to ambient air DOES NOT trigger the color indicator in soda lime and the soda lime can be
desiccated but colored white, thus appearing fresh and safe for clinical use. Soda lime is potentially dangerous to use when desiccated, as CO2 absorption may continue.
In the case of NaOH-containing (sodium hydroxide) absorbents, coloration reverts to white when contact with CO2 ceases, often after a few hours of non-use. This is due to the strongly alkaline nature of NaOH in soda lime.