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Abstract: PO1150

On the Correction of Plasma [Na] in Hyperglycemia

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 902 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Author

  • Segal, Alan, Steady State Nephrology, South Burlington, Vermont, United States
Background

The effect of hypertonic states on metabolism was first considered by Seldin et al in 1949. An empirical equation to correct the plasma [Na] for hyperglycemia was put forth by Katz (NEJM, 1973). About 25 years later, Hillier et al (AJM, 1999) presented another equation based on normal volunteers with experimentally induced hyperglycemia. Both equations are linear with correction factors (in mM [Na]/100 mg/dL [glucose]) of -1.6 (Katz) and -2.4 (Hillier). Non-linearity, however, is apparent in the original data of Hillier, which are better fit by a second-order equation (corrected plasma [Na] = {-3.49 * 10-5 * (plasma [glucose])2 – (3.91 * 10-5 * plasma [glucose]) + 140}). Previous equations also presume normonatremia prior to hyperglycemia and a constant volume of distribution for glucose.

Methods

Here, a new model is proposed that also provides a reasonable fit to the patient data of Seldin et al from 70 years ago (JCI, 1951) and Hillier et al. Unlike previous equations that are based solely on current plasma [glucose], this program takes weight, sex, the presence of edema, and the apparent volume of distribution (aVd) of glucose into consideration. The latter is especially important because the aVd of glucose may change in hyperglycemia.

Results

For example, consider a patient from the 1951 JCI study by Seldin et al: a 59.1-kg edematous patient with cirrhosis who initially had a plasma [Na] of 130 mM when the plasma [glucose] was 126 mg/dL. The program starts by calculating the number of effective osmoles in the ICF and ECF based on the initial labs, and then incorporates the change in ECF volume measured by the investigators, which in this case was +1.9 L.

Following infusion of hypertonic glucose, the plasma [Na] fell to 110 mM at the peak plasma [glucose] of 666 mg/dL. The corrected plasma [Na] predicted are (in mM): 130.9 (Katz), 126.4 (Hillier), and 124.5 (quadratic fit of Hillier’s data); all of which do not compare well with 110 mM. Although the program predicts 121.3 mM, after correction for the change in the aVd of glucose, it predicts 112 mM, in good agreement with the measured value of 110 mM.

Conclusion

Now that making numerous calculations can be done easily and efficiently with apps most physicians have on their phones, it is proposed that equations with linear correction factors be replaced by this new program when clinicians would like to predict or correct the measured serum [Na] in the presence of hyperglycemia.