Bubble oxygenators are intrinsically not
biocompatible
i) Electrokinetic effects —> Protein denaturation
• There exists a layer of electrokinetic force at the gas-blood
interface
• May explain many of the phenomena associated with bubble
oxygenators in clinical practice
• The electrokinetic forces at the gas-blood interface tend to
orientate the proteins so that their hydrophilic groups are in the blood phase
leaving the non-polar groups sticking out into the gaseous phase
• This distortion disrupts the normal configuration of proteins
[protein denaturation], alters their biological specificity and causes
functional alteration
• Some of the altered proteins acquire increased biological
activity (most show a decrease in biological activity)
• Denatured protein aggregates are inherent in bubble oxygenators
Protein
molecules are large and complex. Their activity depends on their shape and
chemical composition. The denaturing or inactivating, of proteins involves the
changing of their shape &/or breaking off attached chemical groups.
Denatured enzymes may loose their catalytic properties, the anti-body-antigen
mechanism may be altered, hormones may loose their function etc.. Surface
electrical charges on these molecules are altered, they become sticky and form
aggregates. Soluble proteins may become insoluble and precipitate. Denatured
globulins may cryoprecipitate (ppt when exposed to hypothermia). Lipid
components freed from lipoproteins coalesce to form fat emboli.
ii) Platelet activation & aggregation
• Secondary to protein denaturation and gas-blood interface
iii) Complement activation
• Secondary to the increased biological activation of some altered
proteins
• See resultant kinin release
iv) Blood cell damage
• It is well known that bubble oxygenators tend to haemolyse red
blood cells
• Mechanism probably due to high shear stresses induced around the
bubble
v) White blood cell destruction
• Due to activation of complement system