Edelman's equation is valid in acute hyponatremia in a porcine model: plasma sodium concentration is determined by external balances of water and cations.
Acute hyponatremia is a serious condition, which poses major challenges. Of particular importance is what determines plasma sodium concentration ([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 how the measured plasma [Na(+)] could be predicted in a porcine model of hyponatremia. Plasma [Na(+)] was estimated from in vivo-determined balances of water, Na(+), and K(+), according to Edelman's equation. Acute hyponatremia was induced with desmopressin acetate and infusion of a 2.5% glucose solution in anesthetized pigs. During 480 min, plasma [Na(+)] and osmolality were reduced from 136 (SD 2) to 120 mmol/l (SD 3) and from 284 (SD 4) to 252 mosmol/kgH(2)O (SD 5), respectively. The following interpretations were made. First, Edelman's model, which, besides dilution, takes into account Na(+) and K(+), fits plasma [Na(+)] significantly better than dilution alone. Second, a common value of alpha = 1.33 (SD 0.08) and beta = -13.04 mmol/l (SD 7.68) for all pigs explains well 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.
Institute of Clinical Medicine, Aarhus Univ. Hospital, Skejby, Brendstrupgaardsvej 100, 8200 Aarhus N, Denmark. christian.overgaard.steensen@ki.au.dk
Christian
C
Overgaard-Steensen
Anders
A
Larsson
Henrik
H
Bluhme
Else
E
Tønnesen
Jørgen
J
Frøkiaer
Troels
T
Ring
D000208:Acute Disease; D000818:Animals; D050034:Antidiuretic Agents / Q000009:adverse effects; D002412:Cations / Q000378:metabolism*; D003894:Deamino Arginine Vasopressin / Q000009:adverse effects; D005260:Female; D007010:Hyponatremia / Q000097:blood / Q000139:chemically induced / Q000503:physiopathology*; D023421:Models, Animal; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000097:blood*; D013552:Swine / Q000502:physiology*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000502:physiology*
D050034:Antidiuretic Agents; D002412:Cations; D012964:Sodium; D003894:Deamino Arginine Vasopressin; D011188:Potassium