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Jørgen Frøkiær

Edelman's equation is valid in acute hyponatremia in a porcine model. Plasma sodium concentration is determined by external balances of water and cations

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  • Anaesthesiology
  • Biomedical Radio Isotope Techniques
  • Nyremedicinsk Afdeling, Medicinsk Center, Aalborg Sygehus Syd
Acute hyponatremia is a serious condition, which poses major challenges. Of particular importance is what determines plasma sodium concentration (plasma [Na(+)]). Edelman introduced an explicit model to describe plasma [Na(+)] in a population as [Na(+)] = alpha*(exchangeable Na(+) + exchangeable K(+))/(total body water) - beta. Evidence for the clinical utility of the model in the individual and in acute hyponatremia is sparse. We therefore investigated whether the actual measured plasma [Na(+)] was equal to the value estimated in a porcine model of hyponatremia. Plasma [Na(+)] was estimated from in vivo-determined balances of water, sodium and potassium according to a conversion of Edelman's equation. Acute hyponatremia was induced with desmopressin acetate (DDAVP) and infusion of a 2.5% glucose solution in anesthetized pigs. During 480 minutes, plasma [Na(+)] and osmolality were reduced from 136 mmol/l (SD=2) to 120 mmol/l (SD=3) and from 284 mOsm/kg (SD=4) to 252 mOsm/kg (SD=5), respectively. First, Edelman's model, which takes into account sodium and potassium, fits plasma [Na(+)] significantly better than dilution alone. Second, common alpha = 1.33 (SD=0.08) and beta = -13.04 mmol/l (SD=7.68) for all pigs explain the plasma [Na(+)] in the individual animal. Third, measured exchangeable Na(+) and calculated exchangeable Na(+)+K(+) per weight in the pigs are close to Edelman's findings in humans, whereby the methods are cross-validated. In conclusion, plasma [Na(+)] can be explained in the individual animal by external balances according to Edelman's construct in acute hyponatremia. Key words: animal model, DDAVP, exchangeable sodium, total body water.
Original languageEnglish
JournalAmerican Journal of Physiology: Regulatory, Integrative and Comparative Physiology
Pages (from-to)120-129
Number of pages9
Publication statusPublished - 2010

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