5. Soda Lime

Soda lime is used to absorb CO2 ain use is to allow the rebreathing of exhaled gases within breathing systems. This is most commonly the circle system,

chemical constituents are calcium hydroxide (Ca[OH]2) 80%, sodium hydroxide (NaOH) 2% and water (H2O KOH] was previously added as an accelerator, but this is one of the strong alkalis which are implicated in the formation of carbon monoxide and Compound A silicates in trace amounts which harden the granules which otherwise would disintegrate into powder. An indicator dye is present which changes the colour of the soda lime as it is progressively exhausted either phenolphthalein (the colour changes from red to white

Soda lime is formed either into granules whose size is 4–8 mesh The size of the granules or spheres is a compromise between providing the largest surface area for absorption without providing excessive resistance to flow kg can absorb up to 250 litres of CO2.

Full equation : CO2 + H2O -> H2CO3 2H2CO3 + 2NaOH + Ca(OH)2 –> Na2CO3 + CaCO3 + 4H2O + Heat

CO2+ Ca(OH)2 - > CaCO3 + H2O

Barium lime (Baralyme): this consists of calcium hydroxide (Ca[OH]2) 80% and barium hydroxide (Ba[OH]2) 20%. Water is incorporated into the structure of Ba (OH)2. The chemical reaction is similar to that of soda lime, although it is less efficient.

constant flow may dry out a canister of soda or barium lime. Under these circumstances, the reaction of the desiccated absorbent with the CHF2 group of isoflurane, enflurane or desflurane can produce high levels of CO.

Compound A: sevoflurane reacts with strong monovalent hydroxide bases, such as those which are used in soda lime and barium lime CO2-absorbers, to produce a number of substances, including compound A.