2C - Carbon Dioxide Absorbents

CO2 Absorbent

• Elminates CO2 by chemical neutralization

• makes rebreathing possble

• conserve anesthetic gases

• decrease OR pollution

• Used by semi close and closed breathing circuits

Exhaled Gas Flow

CO2 Absorbents - Before and After

• pH sensitive indicator dye

• colour changes

colour change

From white to purple

when Co2 absorbent granules are exhausted

due to accumulation of carbonic acid

Chemical neutralization

• CO₂ reacts with water to produce carbonic acid (H₂CO₃)

• Carbonic acid reacts with hydroxides (-OH) forming carbonates (-CO₃), water, and heat

• Water leaches out of granules carrying NaOH or KOH to the bottom of the canister and these strong bases are corrosive to skin

By- products of neutralization

• water and heat

• useful for humidifying inhaled gases

• excess water is drained into a water trap

Soda Lime - fragment easily

• produce alkaline dust (may lead to bronchospasm)

• silica is added to harden granules and decrease dust formation

• degrade inhaled vapors to CO and compounds A

• may revert from purple back to while over time with no recovery of absorptive capacity

Amsorb Plus

• calcium sulfate and polyvinylpyrrolidine added as harder

• do not degrade inhaled vapors

• do no revert to white

Efficiency of CO2 Neutralization

• absorbent granule size

• balance between absorptive efficiency and airflow resistance

• ↓ granule size (↑ surface area) – ↑ absorptive efficiency

• ↓ granule size (↓ space) – ↑ airflow resistance

Mesh Size

• # openings/linear inch in a sieve

• Ex. 4 mesh = 4 quarter-inch openings/linear inch

• Mesh size ranges from 4 – 8 (maximal absorptive efficiency with minimal airflow resistance)

Channeling points

• Exhaled gases only go through a preferred passage (low resistance)

• Bypass the bulk of absorbent granules

• Result from loose packing

• Prevent by gently shaking canister after filling

Absorptive Capacity

• Maximum amount of CO₂ absorbed by 100 g of absorbent

• Influenced by channeling and canister design