Estimating excess glucose, sodium and water deficits in non-ketotic hyperglycaemia

The treatment of solute addition, Na and water losses in hyperglycaemic hyponatraemia is guided by clinical judgement rather than by a quantitative assessment.

We devised an iteration method to compute glucose appearance (G(A)) within the extracellular space, to obtain the PNa (plasma sodium concentration) expected by glucose addition only (PNa(G)). The difference between this and the actual measurement (PNa(1)) was used to compute the attending Na and/or volume depletion, and the PNa expected during correction. The equations were validated on computer-built models, where the electrolyte derangements were simulated, generating true values of plasma glucose (P(G)) and Na concentrations, from which surfeit and deficits were back-calculated with our formulas. We also computed G(A) and PNa(G) on 43 patients who were stratified into a group with normal hydration (PNa(1) = PNa(G)), one with prevalent Na depletion (PNa(1) < PNa(G)), and one with prevalent volume depletion (PNa(1) > PNa(G)). The volume conditions established by our computations were compared by logistic regression analysis with those assessed from clinical laboratory data.

The computer simulations demonstrated that the method gave exact results when only one variable changed, clinically useful estimates in the presence of mixed volume and sodium deficits. There was a strongly significant concordance between the clinical and the quantitative method (P < 0.001). The latter predicted the PNa measured after correction of hyperglycaemia (P < 0.001).

This new method more accurately computes the initial conditions, resulting in a useful stratification of patients which improves the quantitative evaluation and treatment of hyperosmolar coma.