November 2020

DKA: Approach to The Critical Patient

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Andrew C. -

I thought this DKA/HHS episode was quite good but there was one important error and this had to do with the propagation of the notion that hyponatremia due to hyperglycemia is called "pseudohyponatremia". What everyone has been passing along for decades as pseudohyponatremia is totally not the case. The hyponatremia due to the hyperosmolar state of hyperglycemia is indeed an actual hyponatremia caused by the movement of free water shifting from the ICF compartment to the ECF compartment, leading to a dilution of all ions in the ECF compartment. The only real reason we should use the 1.6 to 2.4 mEQ/L correction of sodium for every 100mg/dL increase in glucose is to predict what the sodium would be if we got rid of all the excess glucose. This is a dilutional hyponatremia due to a hyperosmolar state and is real. There is nothing pseudo about this.
Actual pseudohyponatremia is something much different. It is an analytical artifact caused by the way the lab instruments measure sodium using the indirect Ion Selective Electrode method. When there are too many extra proteins floating around as in multiple myeloma, waldenström's macroglobulinema or IVIG therapy, or in the case of sky high lipids, this decreases the water percentage of plasma (normally 93%), and increases the NON-aqueous part of the plasma (normally 7%). This leads to an erroneous lab reading due to the way the instrument works. It's a fake out, hence the term pseudohyponatremia. To correct this, use a DIRECT ISE method to re-measure the serum sodium, such as with an ABG analyzer. Also, in actual pseudohyponatremia, the serum osmolality would be in the normal range. The serum osmolality would be significantly elevated in the hyperglycemic patient. If you suspect pseudohyponatremia, consider checking a lipid panel. If this is normal, and in the right clinical setting, consider sending an SPEP looking for a protein spike. (Of course it's not super helpful for our patients IN the emergency department but I think it's important to at least be aware of this.)

Victor U. -

Totally agree. But don' forgot also for pseudohyponatraemia, another not so rare cause is sampling from a vein with a distal hypotonic infusion running. I got called to a sodium of 70, only to find that the patient had 5% glucose running into their hand on the same arm that the blood sample was taken from.

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Diabetic Emergencies: DKA and HHS Full episode audio for MD edition 52:56 min - 42 MB - M4AC3 DKA & HHS Individual MP3 Files 62 MB - ZIP