Alterations in the plasma water sodium concentration ([Na+]pw) result from changes in the total exchangeable sodium (Na e), total exchangeable potassium (K e), and total body water (TBW). The empirical relationship between the [Na+]pw and Na e, K e, and TBW was originally demonstrated (Edelman IS, Leibman J, O'Meara MP, and Birkenfeld LW. J Clin Invest 37: 1236-1256, 1958), where [Na+]pw = 1.11...