CO2 Absorption Flashcards
how does CO2 cause acidosis?
CO2 combines with H2O to form H2CO3 (carbonic acid)
how does absorbent work?
-soda lime or calcium lime (salts) neutralize carbonic acid to water and energy (heat)
what is the most common absorbent?
soda lime
what are the ingredients of different absorbents?
- 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
how does pH indicator of absorbent work?
-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
what is mesh?
the number of holes per linear inch of a screen
how many mesh are most CO2 absorbents?
4-8 (more so 8) (bigger the number, the smaller)
what is dessicated absorbent?
very dry absorbent
*leads to higher volatile gas degradation
What are volatile agents degraded to with dessicated absorbent?
- desflurane to carbon monoxide (CO)
- sevoflurane to compound A
- degradation is worst with KOH
- Amsorb is a newer CO2 absorbent resulting in less degradation
what is Compound A?
by-product of sevoflurane degradation by absorbent
*nephrotoxic at 25-50 ppm (easily created with low flows)
what increases the risk of Compound A formation?
- 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
What is the benefit of Amsorb absorbent use?
-allows for lower flows of Sevo without degradation into Compound A
what is channeling?
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
how can you prevent dessication and exhaustion of absorbent?
- 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)
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?
- 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