chloride, adjusted for sodium abnormalities, Clcorr
chloride is arguably the most underestimated quantity in clinical acidbase practice. many, especially surgical patients, present with metabolic acidosis and a low base excess, without raised endogenic acid production: they may be well oxygenated and have sufficient systemic and regional circulation.
these patients almost invariably have been treated with fluids containing equal amounts of chloride and sodium - this includes isotonic saline, most colloid preparations and most dextrose solutions. less common reasons are severe diarrhoea or chronic chloride reabsorption in patients with urinary bladder reconstructions with intestinal loops.
infusion fluids and body fluids must be electroneutral, that is they contain equal amounts of positive ions and negative ions.
the ions dominating this balance are Na+ and Cl-, there are also lesser quantities of other kations and anions.
whenever the Na+ concentration increases in an aqueous solution like plasma, some negative ion concentration must follow in exactly equal quantities. in pure strong ion solutions in water this can only be OH- or, in liquids exposed to CO2, HCO3-. in solutions containing weak acids like albumin some of the increase in anionic charges is due to increased weak acid dissociation, too. still, even in these solutions, the bulk of increase in anionic charge stems from increases in bicarbonate.
as chloride cannot be metabolised or evaporate, raising the concentration of Cl- relative to Na+ simply reduces the space left over for HCO3-.
as long as PCO2 remains unchanged, the classical Henderson -Hasselbalch- equation tells us that the solution will become more acidotic. "normal saline" with its high chloride content is the typical culprit.
lowering Na+ relative to Cl- has exactly the same effect of narrowing the space left over for HCO3-. this is why even electrolyte free dextrose will push a patient to the metabolically acidotic side.
as it is the difference between the two, Na+ and Cl-, that matters and not their absolute values, our programme adjusts Cl- for any concomitant changes in Na+ by simple addition and subtraction: Clcorr = Cl- + 142mmol/l - Na+
(deriving Clcorr by the proportional changes, Clcorr = Cl- * (142mmol/l / Na+), is preferred when looking for concentrational and dilutional effects.)
