2018A04 Outline the hazards associated with the use of CO2 absorbents within a circle
breathing system and how the risks can be minimized.

 

List:

·     Physical hazards

·     Degradation products

·     Other

·     Ingredients: each type

 

Physical hazards of CO2 absorbent:

Heat

·  Worst with baralyme + sevo (150°C)

·  Risk of burns, fires, explosions

·  Fix: use a well sealed well-insulated canister. Change when depleted.

·  Fix: turn off when not in use. Change regularly, after excessive use, or if in doubt.

Spill

·  Risk of injury to lungs, skin, eyes

·  Fix: use a well sealed canister, careful not to spill.

 

Harmful degradation products:

Compound A

·  Reaction sevo + absorbent

·  Baralyme > Sodalime >> Amsorb and Litholime

·  More likely if high sevo%, low fresh gas flow rate, high temp, fresh absorbent

·  Nephrotoxic in rats at 150-200ppm

·  Fix: don’t use baralyme

·  Fix: use FGFR>2L/min; limit sevo to 2MAC-hours if FGF 1-2L/min

Carbon monoxide

·  Reaction absorbent + CHF2 (difluormethyl) moiety in volatile

·  Desflurane > enflurane > isoflurane >> others

·  More in baralyme > sodalime

·  More if absorbent hot and dry (e.g. left on over weekend)

·  HbCO can rise to 35%. Binds to Hb with 250x higher affinity than O2.

·  Fix: avoid baralyme; avoid continuous use without break

·  Fix: ensure machine turned off after use; check CO2 canister before use; replace if in doubt

·  Fix: use sevo

Other

·  Formaldehyde

·  Methanol

 

Other:

Unrecognised exhaustion

·  When near depleted, lime colour can change back to “fresh” if left unused

·  Unused OH- ions in the core migrate to the surface.

·  Fix: check before each case

·  Fix: use capnography in every GA

Airway resistance

·  4-8 mesh optimal for balance between ↓ airway resistance and ↑ surface area

·  Risk of breathstacking in children

·  Fix: use a Mapleson circuit instead

Awareness

·  Risk if canister changed during anaesthesia

·  Fix: change between cases if possible

·  Fix: administer IV anaesthetic temporarily

 

Ingredients: (unlikely to score marks)

Sodalime

·  80% Ca(OH)2

·  <4% NaOH

·  16% water(to accelerate reaction)

·  Indicator (ethyl violet or phenolphthalein)

·  Silica (hardening agent)

Baralyme

·  80% Ca(OH)2

·  <20% BaOH

·  Water is incorporated into lime, making it less efficient

Amsorb plus

·  >75% Ca(OH)2

·  CaCl2

·  15% H2O

Litholime

·  >75% Ca(OH)2, small amount LiOH

 

 

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