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.
Overgaard-Steensen
Christian
C
Institute of Clinical Medicine, Aarhus Univ. Hospital, Skejby, Brendstrupgaardsvej 100, 8200 Aarhus N, Denmark. christian.overgaard.steensen@ki.au.dk
Larsson
Anders
A
Bluhme
Henrik
H
Tønnesen
Else
E
Frøkiaer
Jørgen
J
Ring
Troels
T
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