Exposure to which of the following is most likely to deactivate the color indicator in soda lime absorbent?
- (A) Fluorescent lights
- (B) Compound A
- (C) Water
- (D) Heat
Ethyl violet is a pH-activated color indicator that is added to the soda lime used in the carbon dioxide (CO2) absorbent canister in the anesthesia circuit. It causes the soda lime to change from white to a violet color when the pH of the absorbent decreases due to CO2 absorption. This color change indicates that the absorptive capacity of the soda lime is exhausted. Prolonged exposure to bright lights, including fluorescent lights, can deactivate the dye, making it an unreliable indicator of the absorptive capacity of the soda lime. In this event, capnography is the most sensitive indicator of exhausted soda lime. Inspired CO2 will be greater than zero if the soda lime is exhausted.
Water must be present for the chemical reaction necessary for CO2 absorption to occur. Heat is produced by the process of converting CO2 to a carbonate or bicarbonate form. Exposure of sevoflurane to soda lime produces compound A (fluoromethyl-2,2-difluoro-1-[trifluoromethyl] vinyl ether). Exposure of soda lime to compound A, water or heat has not been shown to deactivate the color indicator in the absorbent.
Bibliography
Ehrenwerth J, Eisenkraft JB, Berry JM , eds. Anesthesia Equipment: Principles and Applications. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2013:104.
Andrews JJ, Johnston RVJr, Bee DE, Arens JF . Photodeactivation of ethyl violet: a potential hazard of Sodasorb. Anesthesiology. 1990;72(1):59–64.
Answer: A