2015B13 Describe the fuel cell and the paramagnetic oxygen analyser.
Discuss their use in anaesthetic practice.

 

List:

·     Paramagnetic analyser: diagramme, principles, pros, cons

·     Fuel cell: diagramme, how it works, pros, cons

 

Paramagnetic analyser:

Diagramme

Principles

·   Paramagnetic = attracted towards a magnetic field

·   Due to outer shell electrons being spun in the same direction

·   Oxygen has two unpaired outer shell electrons and is strongly paramagnetic

·   Nitric oxide is weakly paramagnetic

·   Other gases e.g. CO2, N2 are diamagnetic = repelled by the magnetic field

Pros

·   Rapid, for breath to breath analysis

·   Accurate

·   Requires infrequent calibration

·   No exhaustible reagents or components

Cons

·   For gas only

 

Fuel cell:

Diagramme

 

Cathode: O2 + 4e- + 2H2O -> 4OH-

Anode: 2Pb + 4OH- -> 2PbO + 2H2O + 4e-

How it works

·   O2 diffuses through the membrane

·   pO2 is rate limiting for REDOX

·   Ammeter measures resulting current

Pros

·   No external power source required

·   Cheap

·   Can be used for gases or blood

Cons

·   Slow (20 seconds)

·   Requires more frequent calibration with 100% and 21% O2

·   Lifespan 12 months, dependent upon exposure to oxygen

 

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