Quantitative Assessment of the Abnormalities of Hyperosmolar Coma when Glucose Excess is Larger than Na Deficit

Abstract

Computing Na and water deficits of hyperosmolar coma (HC) is important in correcting the derangement, to avoid unwanted iatrogenic electrolyte derangements and brain oedema. This paper derives and applies formulas valid when GA (glucose accumulation) >2·ΔNa (sodium loss), with or without ΔV (water depletion). We built a model system and wrote the equations describing the relationships between volume and concentration of solutes within the body water compartments. HC was simulated on computer experiments by adding GA in different amounts combined with a large variety of ΔNa and ΔV. The ensuing concentrations in Na (PNaNone.₁) and glucose (PG₁) were used to identify the condition GA >2 · ΔNa, ΔV=0 or ≠ 0, and then, with original formulas, to back calculate GA, ΔNa and ΔV. These same calculations were applied to 31 patients with HC. The procedure to recognize the conditions under investigation unerringly discarded all simulations except those characterized by GA >2 · ΔNa, with or without ΔV. When ΔV=0, the computations yielded values identical to the true ones for GA and ΔNa (R²=1.00, p<0.0001). When ΔV was present, the correlation coefficients between calculated and true values were 0.92 (p<0.001) for GA, 0.73 (p<0.001) for ΔNa, 0.74 (p<0.001) for ΔV in computer experiments, while they were R²>0.47<0.95 (p<0.001) in patient studies. The accuracy in computing solute and water changes demonstrates the validity of our model system of HC, and of the calculation formulas, which can be used to quantitatively evaluate the deficits in Na and volume, as well as the addition of glucose, improving the effectiveness of treatment.

Key words

hyperosmolar coma - hyperglycaemia - hyponatremia - sodium deficit - body fluids

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