CO2 Absorption

Question 1

how does CO2 cause acidosis?

Answer 1

CO2 combines with H2O to form H2CO3 (carbonic acid)

Question 2

how does absorbent work?

Answer 2

-soda lime or calcium lime (salts) neutralize carbonic acid to water and energy (heat)

Question 3

what is the most common absorbent?

Answer 3

soda lime

Question 4

what are the ingredients of different absorbents?

Answer 4

• soda lime: NaOH (sodium hydroxide)
• calcium lime: Ca(OH)2 (calcium hydroxide)
• KOH (potassium hydroxide) (least used)
• a little water added to all
• silica added to decrease dust and resistance

Question 5

how does pH indicator of absorbent work?

Answer 5

-turns white absorbent to purple (or pink) as acid levels
builds indicating absorbent exhaustion
-replace with 50-70% (usually 50%) color change
-absorbent can revert back to original color with rest, but
absorbency is NOT restored

Question 6

what is mesh?

Answer 6

the number of holes per linear inch of a screen

Question 7

how many mesh are most CO2 absorbents?

Answer 7

4-8 (more so 8) (bigger the number, the smaller)

Question 8

what is dessicated absorbent?

Answer 8

very dry absorbent

*leads to higher volatile gas degradation

Question 9

What are volatile agents degraded to with dessicated absorbent?

Answer 9

• desflurane to carbon monoxide (CO)
• sevoflurane to compound A
• degradation is worst with KOH
• Amsorb is a newer CO2 absorbent resulting in less degradation

Question 10

what is Compound A?

Answer 10

by-product of sevoflurane degradation by absorbent

*nephrotoxic at 25-50 ppm (easily created with low flows)

Question 11

what increases the risk of Compound A formation?

Answer 11

• high concentrations of Sevo
• long anesthesia time (> 2 MAC hours)
• Low flow techniques (< 2 L/min)
• *with typical CO2 absorbents, must run Sevo with high flows (> 2 L/min)
• *longer cases may want to run Sevo at O.5 MAC over a few hours to stay below 2 MAC hours

Question 12

What is the benefit of Amsorb absorbent use?

Answer 12

-allows for lower flows of Sevo without degradation into Compound A

Question 13

what is channeling?

Answer 13

absorbent exhaustion in areas where gas enters the absorber and along the canister walls
-baffles in the absorber direct gas flow through the center to minimize channeling

Question 14

how can you prevent dessication and exhaustion of absorbent?

Answer 14

• avoid absorbents with KOH if possible
• create/enforce policies to prevent dessication
• turn off all gas flow when machine is not in use
• change absorbent on scheduled basis
  (i. e. once a week on the same day)
• change compact canisters frequently
• use low flows as much as possible (high flows dry out)

Question 15

what can you do if you notice your patient’s inspired CO2 increasing in the middle of a case and you have 70% of absorbent is purple?

Answer 15

• most likely exhausted absorbent
• FGF 0.3- 0.5 L/min almost total rebreathing
• increase flows of 5-8 L/min allowing little absorbent work and CO2 is flushed to scavenger via high flow
• change absorbent at end of case