chloride, adjusted for the proportional change of sodium from its normal value
(Chloride is arguably the most underestimated quantity in clinical acidbase practice.)
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Deriving Clcorr by the proportional changes, is preferred when looking for concentrational
and dilutional effects.
When extracellular fluid looses or gains (pure) water, Na+ and Cl-
get concentrated or diluted in synchrony with each other, their values and their difference change by the same proportional factor.
Correcting Cl- by this factor will show a normal chloride value, as long as no other change than water loss or gain has changed it.
As the absolute difference between the two ions "contracts" or "expands" by the same factor, the space left over for the second most common negative ion species:
HCO3- also "contracts" or "expands".
As long as PCO2 remains unchanged, the classical Henderson -Hasselbalch- equation tells us that the solution will become more alkalotic, when pure water gets lost:
"contraction alkalosis", and more acidotic, when pure water gets added: "expansion acidosis".
