CO2 Absorption Flashcards
What is the purpose of the CO2 absorber?
chemical neutralization of CO2
What are basic components of CO2 absorber?
base, acid (carbonic), base, end-product (water, carbonate, heat)
What is carbonic acid (H2CO3) formed by?
CO2 + H2O
What are the basic end products of CO2 absorption?
H20, a carbonate, heat
Classic absorber had two issues, what were they?
leaks, couldnt change during case bc it would ruin circle system integrity (modern ones can)
4 common absorbents used?
Soda lime (NaOH lime), Amsorb plus (CaOH lime), Baralyme, Litholyme (LiOH)
Some Like As + Bs Like Me
What is in soda lime?
Ca(OH)2 (80%), H2O (15%), NaOH (4%), KOH (1%), silica (0.2%) - hardness,
What is the function of silica?
for hardness and to prevent dust formation
How much CO2 can Soda Lime absorb? (per lb Ca(OH)2 and per L)
26 L of CO2/100g of absorbent
1 lb Ca(OH)2 / 0.59 lbs CO2
Why is moisture essential in most absorbents?
Reaction only occurs in the presence of ions that form in H20
What is the generic reaction of soda lime?
CO2 w/ H2O forms H2CO3 which reacts w/ hydroxides to form Na/K carbonate (-CO3 -2), H2O, heat
What is the slow reaction in soda lime?
CO2 w/ Ca(OH)2 to form CaCO3, H2O, heat
Amsorb plus is AKA ______?
CaOH lime
What are basic components of CaOH lime?
Ca(OH)2 (80%), H2O (16%), CaCl2 (1-4%), calcium sulfate and PVP - hardness
How much CO2 and Amsorb Plus bind?
10 L of CO2 / 100 g Amsorb Plus
What is the general reaction of CaOH Lime?
CO2 + H2O makes H2CO3 + Ca(OH)2 makes CaCO3, H2O, heat
Baralyme was pulled from the market for what reason? Why?
Fire and explosion risk bc no water in absorbent made it more flammable
What is Baralyme made of?
80% CaOH and 20% BaOH
What does mesh mean?
screens with 4-8 holes per linear inch, classification of granule size of absorbents
How is a mesh achieved? (Ie, what size granules used)
a combination of small and large granules
Does Baralyme use a hardening agent?
no
What is Baralyme’s absorptive efficiency?
26 L of CO2 / 100 g
True or false Baralyme have water in it.
False
Litholyme (LiOH)/Lithium Hydroxide Monohydrate also comes in an ___________ formulation.
anhydrous
What are the basic components of Litholyme?
75% LiOH, 12-19% H2O, < 3 % LiCl
What is the general reaction for Litholyme?
LiOH w/ H2O w/ CO2 makes LiCO2 + H2O + heat
How much CO2 does Litholyme absorb?
1 lb LiOH per 0.91 lb CO2
Litholyme is _______ efficient but _______ expensive.
more, more
How can you tell when the absorber needs to be replaced?
color conversion indicates a rise in pH (basic)
What color is the most common color indicator in absorbents and whats its critical pH?
ethyl violate, 10.3
When should the absorbent be changed?
w/ 50-70% color change
What can happen in NaOH/soda lime formulations of absorbent - in regards to color change? Why?
If absorbent sits idle for a while it can revert from purple back to white, this does not mean the soda lime regenerated. Subsurface ca hydroxide reacts regenerates hydroxide at surface, changing pH and therefore the color back to white.
Name indicator dyes, color when fresh, color when used.
Phenolphthalein, White, Pink Ethyl Violet, White, Purple Clayton Yellow, Red Yellow Ethyl Orange, Orange, Yellow Mimosa 2, Red, White
Describe the shape of granules. Whats the significance?
Irregular, increased surface area.
Why are just small granules bad? What’s better?
small granules increases resistance; mix of small and large minimizes resistance for a sacrifice in capacity of CO2 absorbance
Why is it better for granules to be hard?
excessive powder causes channeling, resistance, caking
What should an absorbent’s hardness number be?
> 75
Describe the channeling phenomena.
preferred path of gas through absorber (lowest resistance), results from loosely packed granules.
absorbent along channels may be used up but not visible causing CO2 monitoring to be affected
What percentage of absorbent canister volume is air?
48-55%
How have manufacturers tried to mitigate channeling in absorbent?
Using polymer to bind granules into pre formed channels
What is compound A?
When sevoflurane is degraded by strong base in absorbent (KOH, less so NaOH) forms compound A in concentrations nephrotoxic to rats (does not happen in absorbents w/ no KOH or NaOH). Does not happen in new absorbents.
What does the manufacturer recommend to avoid the production of compound A?
no more than 2 MAC hours at flows 1 to < 2 L/min
MAC hour = MAC x hours of volatile given
What’s a MAC hour?
MAC hour = MAC x hours of volatile given
True or False there is no research or evidence to show that compound A is nephrotoxic in humans.
True
How to prevent compound A from forming w/ sevoflurane use?
FGF > 2 L/min, not based in evidence
What forms when desiccated NaOH and KOH containing absorbents are not used for 24-48 hours?
CO
What causes the desiccation of absorbents?
high flow through a system for a long time (leaving gas on over weekend) dries out the absorbent.
How does CO form in absorbents and what types of absorbents can it form in? What volatile is associated with the highest accumulation of CO?
desiccated absorbent forms CO, a slow rxn w/ volatiles.
only happens in dried out NaOH and KOH
desflurane
Do new absorbents w/out NaOH and KOH form CO if desiccated?
No
What are safety recommendations from Anesthesia Safety Foundation for absorbents? (6)
turn off gas flow when machine not in use
change absorbent regularly
change when color change indicates exhaustion
change all absorbent not just one canister
change absorbent when unsure of hydration (FGF on for long time)
low flows preserves granules
