Computation of the excess glucose and Na deficit of hypo-osmolar hyponatremic hyperglycaemia.

Exact computations of glucose accumulation (GA, mM) and Na anions deficit (DeltaNa, mEq) can be obtained in hypo-osmolar hyponatremic hyperglycaemia (HHH), where plasma osmolality (POsm) is lower than normal. In this condition, GA - DeltaNa = POsm x TBW (total body water). GA is given by plasma glucose concentration (PG(1)) times extra-cellular volume (ECV), calculated as TBW - ICV (the known intra-cellular volume). The changes in solute content can then be computed from their concentrations. This model was verified on computer-simulated patients to whom GA was added in variable amounts, lower than those of DeltaNa subtracted, generating known ICV, ECV, PNa(1), and PG(1). True computer-generated values were identical (the correlation coefficient R(2) = 1, p < 0.0001) to those computed from solute concentrations with our formulas. These same calculations were applied to patients with HHH, using exclusively the measured PNa(1) and PG(1) to compute solute and solvent changes. The results were significantly correlated to true data obtained by balance studies (R(2) = 0.89, p < 0.001). The mathematical model correctly computes DeltaNa and GA in HHH, where patients can therefore benefit from accurate replacement strategies.