2.8 Sodalime Flashcards
Name the compounds used to absorb
carbon dioxide in the breathing system.
- Soda lime
- Baralyme or barium lime
- Litholyme or lithium lime
- Amsorb
- Amsorb Plus
- Dragersorb and Medisorb
Soda lime
Commonly used, it has been proven that presence of sodium hydroxide,
at any level,
provides the basis for anaesthetic agent dehalogenation,
which can lead to formation of
compound A and carbon monoxide.
Baralyme or barium lime
It is made of 80% calcium hydroxide and 20% barium hydroxide.
This is less efficient than soda lime and also
produces compound A more quickly.
Litholyme or lithium lime
Also an effective carbon dioxide absorbent,
litholyme is free of the strong bases (NaoH, KoH)
and does not produce compound A or carbon monoxide.
Lithium chloride acts as the catalyst to accelerate the
formation of calcium carbonate.
Amsorb
Contains calcium hydroxide and calcium chloride
and is not associated with the formation of
carbon monoxide or compound A
Amsorb Plus
It is a new generation carbon dioxide absorbent,
free from strong alkali metal hydroxides.
It utilizes calcium hydroxide as the
active base with minor constituents
that promote speed and capacity of absorption.
Amsorb Plus is specifically designed for low
and minimal flow anaesthesia.
Dragersorb and Medisorb
- These are produced by Drager and GE healthcare, respectively, with
varying proportions of constituents.
Describe soda lime in detail.
- Constituents
- 94% calcium hydroxide
- 5% sodium hydroxide,
- small amount of potassium hydroxide (0.1%)
- silica to prevent disintegration.
- A dye or colour indicator such as
ethyl violet is also added,
which changes the colour when
the soda lime is exhausted.
This happens at pH < 10. - pH 13.5
Moisture content 14%–19% - 1 kg absorbs 120 L of carbon dioxide
- When exhaled gases reach the canister,
carbon dioxide absorption takes
place and heat and water are produced. - The warmed and humidified gas
rejoins the fresh gas flow (FGF). - In a patient with tidal ventilation of 6 L/min
and Co2 production of 250 ml/min,
the soda lime will be exhausted in 6 hours at FGF of 1 L/min
and in 8 hours if the FGF is 3 L/min.
What is the chemical reaction during the absorption of co2 by soda lime?
Co2 + H2o → H2Co3
then
H2Co3 + 2 KoH →K2Co3 + 2 H2o + Energy
then
K2Co3 + Ca(oH)2→ CaCo3 + 2KoH
Each mole of Co2 (44 g) reacted produces one mole of water (18 g).
________
The overall reaction is
Ca(oH)2 + Co2 → CaCo3 + H2o + heat
What are the harmful products that are formed when using soda lime?
- Compound A
- Carbon Monoxide
- Other insignificant substances like methane, acetone, ethanol, etc.
Compound A
Is a fluoro methyl ether
produced when sevoflurane is used
with soda lime due to dehydrohalogenation
in the presence of KoH.
Factors that increase the production of compound A are
° High sevoflurane
° Increasing temperature
° Low FGF
° Use of baralyme
Carbon Monoxide
Occurs when inhalational agents with CHF2 moiety
such as desflurane,
enflurane,
and isoflurane
are used with desiccated soda lime granules.
This happens when the system is left unused for a long time.
This can lead to formation of carboxyhaemoglobin
and can be significant in smokers
especially when very low flows are used.
- Factors increasing the production of CO include
- ° Type of inhaled anaesthetic agent
magnitude of Co production from greatest to least is
desflurane > enflurane > isoflurane > sevoflurane)
- ° High absorbent dryness
- ° Type of absorbent
(at a given water content, baralyme produces more CO than soda lime) - ° Increased temperature
- ° Higher anaesthetic concentration
What is the size of the soda lime granules?
The typical size is expressed as between 4–8 mesh.
It means the granules will
pass through a mesh with 4–8 strands per inch in each axis.
How does this affect its performance?
The uniformity in size is necessary to provide a smooth flow.
They should provide larger surface area
but lesser resistance to flow.
Bigger molecules would cause gas channelling,
and smaller granules can increase the resistance to gas flow.
What are the uses of using soda lime?
- Anaesthetic use
- Non anaesthetic use—
in submarines and recompression chambers - Metabolic monitoring—
in alkaline fuel cells to extract carbon dioxide as it affects the measurement
What are the advantages of Soda lime?
Advantages
- Permits low flows without rebreathing carbon dioxide,
making the system cost effective
- Permits low flows without rebreathing carbon dioxide,
- Less waste and pollution
- Humidification of inspired gases due to the inherent exothermic reaction
is the colour indicator always accurate and represent the usage of soda lime?
No.
The decrease in pH causes the indicator to change colour,
so any product that causes a decrease in pH
can mimic an exhausted soda lime.
In partial exhaustion,
the carbonic acid levels increase and cause the change
in colour of the indicator.
If the soda lime is unused,
then the free hydroxyl ions from the depth of the canister
migrate to the surface and neutralise the acid,
reverting the colour change.
As a result, the soda lime appears fresh
although it is partially exhausted.
What are the clinical signs of soda lime exhaustion?
- Increased spontaneous respiratory rate in the absence of muscle relaxant
- Increase in sympathetic drive
- Respiratory acidosis
- Increased surgical bleeding due to hypertension and coagulopathy
What are the pros of using a circle system?
Advantages
- Economy of anaesthetic consumption
- Warming and humidification of the inspired gases
- Reduced atmospheric pollution
What are the cons of
using a circle system?
Disadvantages
- Unstable if closed-system is used
- Slow changes in the inspired anaesthetic concentration
with low flows and out-of-circuit vaporiser
- Slow changes in the inspired anaesthetic concentration
What are the components of a circle system
- CO2 absorber canister
- Breathing bag
- Unidirectional inspiratory and expiratory valves
- Fresh gas supply
- Pressure-relief valve
- Corrugated hoses and a Y-piece
Circle system - rough dimensions of tubing?
The body of the absorber is connected to the patient
by means of inspiratory and expiratory tubes
and a Y-piece the size of which is important
when anaesthetising paediatric patients
as very small tidal volumes may not generate
enough pressure to open the valves effectively.
The effective dead space of the Y-piece is larger than it appears,
and so there can be rebreathing of exhaled gas.
These difficulties are overcome by the use of
purpose-built infant absorbers and paediatric tubing and Y-pieces.
