Odom's indicator and Soda Lime (anaesthetic Equipment)

Odom's indicator is a device used for locating the epidural space in regional anaesthsia.[1] The device works on Dogliotti's principle[2] by finding an area of decreased resistance to injection. It was originally designed on the assumption that the pressure in the epidural space was negative. This device is no-longer popular and alternative methods (e.g. loss of resistance to saline, loss of resistance to air) are now used
Soda lime
Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.[1][2]
It is made by treating slaked lime with concentrated sodium hydroxide solution.

Compostion of soda limeGrace SODASORB is a granulated compound consisting primarily of hydrated lime (above 80% Ca(OH)2) blended with small amounts of sodium hydroxide (below 4% NaOH). SODASORB does not contain potassium hydroxide (KOH), which was removed in January 2000. SODASORB also contains water (12% to 19%, avg. 16% H2O) and a fractional content of an exhaustion indicator dye. Function of soda limeSoda lime is used in breathing systems to absorb expired CO2 during anaesthesia. It can be incorporated in a Mapleson C system or a circle system. The reaction:CO2 + 2NaOH → Na2CO3 + H2O + heatNa2CO3 + Ca(OH)2 → 2NaOH + CaCO3CO2 in solution reacts with sodium hydroxide to form the respective carbonates, which then react with calcium hydroxide to produce calcium carbonate, replenishing sodium hydroxide. Heat and water are produced during the reaction. Exhaustion of its activity is indicated by dyes; the most common one changes from pink to white.Size of granulesThe size of the soda lime granules is 4-8 mesh (i.e. will pass through a mesh of 4-8 strands per inch in each axis or 2.36–4.75 mm).Key learning points:-Exhaled gases are circled back to the canister, where CO2 absorption takes place and water and heat are produced. The warmed and humidified gas joins the fresh gas flow to be delivered to the patient.
-Compound A is a pentafluoroisoproprenyl fluoromethyl ether (an olefin). Fears over production of this have led to the drug’s data sheet in the USA prohibiting its use at low flows. This restriction does not apply in the UK.
-Carbon monoxide production has occurred when volatile agents containing the CHF2 moiety (enflurane/isoflurane/desflurane) are passed over soda lime that has become desiccated or dried out.