Week 8 CO2 absorption Flashcards
Why is granule hardness important? How is it tested? What should the hardness number be?
- excessive powder → channeling, resistance, caking
- tested with steel ball bearings & screen pan
- % of original remaining = hardness number
- hardness number should be >75
Describe the gas flow through the CO2 absorber during the inhalation phase of respiration.
What is the absorptive capacity of baralyme?
26 liters of CO2 per 100 grams absorbent granules
In CO2 absorbers, color conversion signals….
absorber exhaustion
Describe how Compound A can be a problem with CO2 absorbents. What do you manufacturers recommend related to this issue? How do practitioners avoid this problem?
- CO2 granules degrade volatile anesthetic agents to some extent, especially sevoflurane
- when degraded by a strong base in CO2 absorbents (containing KOH and to a lesser extent, NaOH), sevoflurane forms Compound A at concentrations which have been demonstrated to be nephrotoxic in rats
- does not appear to be an issue with absorbents with no KOH/NaOH
- Manufacturer recommens no more than 2 MAC hours at flow rates of 1 to <2 L/min
- MAC hours = MAC x hours of inhalation agent given
- 1 MAC x 2 hours = 2 MAC hours
- 1/2 MAC x 4 hours = 2 MAC hours
- MAC hours = MAC x hours of inhalation agent given
- Most practitioners use at least 2 liters of FGF with sevo
- although this practice is not evidenced based necessarily no connection between renal damage and sevoflurane use has been determined after extensie clinical use
- ALSO, new absorbents do not appear to form Compound A
- although this practice is not evidenced based necessarily no connection between renal damage and sevoflurane use has been determined after extensie clinical use
Describe the calcium hydroxide reaction.
Describe the soda lime reaction.
- carbon dioxide combines with water to form carbonic acid
- carbonic acid reacts with hydroxides to form sodium (or potassium) carbonate and water and heat
Which volatile anesthetic is associated with the highest accumulation of carbon monoxide?
desflurane
How many liters of CO2 are 100g soda lime capable of absorbing?
26 liters of CO2/100 g of absorbent granules
What is channeling? Why is it a problem? How do some manufacturers try to prevent?
-
preferential passage of exhaled gas flow through absorber via pathways of low resistance
- results from loosely packed granules
- air space occupies 48-55% of the volume of the canister
- absorbent along channels may exhaust
- CO2 may filter though channels not visible
- CO2 monitoring may be affected
- some manufacturers now use a polymer to bind the granules in pre - formed channels to prevent channeling
What is the composition of Baralyme?
- 80% calcium hydroxide
- 20% barium hydroxide
- small amounts of sodium hydroxide and potassium hydroxide may be added
- (no hardening agent)
- (no water)
- granules are 4-8 mesh
What is the makeup of calcium hydroxide lime (aka amsorb plus)?
- 80% calcium hydroxide
- 16% water
- 1-4% calcium chloride
- calcium sulfate and polyvinylpyrrolidine
- added hardness
T or F: Color of the absorbent can revert back with rest.
True;
**especially in NaOH containing formulations**
1 pound of lithium hydroxide absorbs how many pounds of carbon dioxide?
.91 pounds of carbon dioxide
Desribe the litholyme reaction.
end product: lithium carbonate, water, heat
State the color of the indicator when absorbent is fresh vs when absorbent is exhausted for phenolphthalein, ethyl violet, clayton yello, ethyl orange, and mimosa 2.
Why was baralyme voluntarily pulled from the market?
- implicated in fires
- no water in makeup of baralyme
Describe the size and shape selection of absorbent granules.
- 4-8 mesh → granule size = number of openings per inch in a sieve through which particles can make it through
- irregular shape = increased surface area
- small granules increase resistance
- blend of small and large minimize resistance with little sacrifice in absorbent capacity
What is the makeup of litholyme (lithium hydroxide monohydrate)?
- 75% lithium hydroxide
- 12-19% H2O
- <3% lithium chloride
**note: there is also an anhydrous formulation**
What is the most common CO2 absorber and what is its critical pH?
ethyl violet
critical pH = 10.3
Replace CO2 absorbent when ___ - ___ % color change.
50-70%
Calcium hydroxide lime is capable of absorbing how many liters of CO2 per 100 g absorbent granules?
10 liters of CO2 / 100g of absorbent granules
What is the make up of soda lime?
- 4% sodium hydroxide
- 1% potassium hydroxide
- 15% H2O
- 0.2% silica
- 80% calcium hydroxide
List the Anesthesia Safety Foundation Recommendation on Safe Use of Carbon Dioxide Absorbents.
- turn off all gas flow when the machine is not in use
- change absorbent regularly
- change absorbent whenever the color change indicates exhaustion
- change all abosrbent, not just one canister
- change absorbent when uncertain of the state of hydration, such as if FGF is left on for extended time
- low flows preserve humidity in granules
1 pound of calcium hydroxide can absorb how many pounds of carbon dioxide?
.59 pounds of carbon dioxide
Describe the flow of gas during the exhalation phase of respiration.
- gases flow through the mask → into the rebreathing bag → and out the apl valve
- fresh gas continues to flow from the common gas outlet at the machine into the common gas inlet at the absorber
A problem with CO2 absorbents is the accumulation of carbon monoxide. How and why does this happen? What can happen to patients?
- CO known to accumulate in desiccated (dry) NaOH and KOH containing absorbents when they are not used for 24-48 hours
- high flow through a system for prolonged time (such as if one forgets to run down the O2 flow over the weekend) = dries it out
- with dried out absorbent, a slow reaction occurs with the volatile anethetic agents and absorbents that produces CO
- **can result in critically high levels of carboxyhemoglobin in exposed patients**
