Soda Lime, Carbon Dioxide Absorbent Granules is a high-grade granular product that effectively absorbs carbon dioxide that is produced as an anesthesia by-product. It is a mixture of calcium hydroxide Ca(OH)2 also known as lime plus a smaller amount of sodium hydroxide NaOH. Upon exposure to carbon dioxide CO2, the calcium hydroxide converts to calcium carbonate Ca (CO3). This prevents CO2 buildup in a re-breathing circuit. The sodium hydroxide acts as a catalyst in the process. No potassium hydroxide (KOH) is present in soda lime; this helps to avoid the formation of toxic compounds such as Compound A and carbon monoxide. Soda Lime has a pH color change indicator that changes from white to violet when the soda lime needs to be changed. It will eventually return to its original color if not changed. Therefore, a good rule of thumb is to replace the soda lime every time the vaporizer is filled.