Acidosis in DKA

Hi Robert,

Thanks for the feedback! In answer to your question about magnesium repletion, I actually much prefer IV Mg++ rather than PO Mg++ in this situation.

In sick DKA, often the rate limiting step for correcting the acidosis ends up being the serum potassium, ie: you can't rapidly give the patient enough insulin to correct their acidosis because you keep dropping the K+ too far. As such, repleting the potassium aggressively from the very beginning is a major priority in a sick DKA patient. If the patient is hypomagnesemic, then it is going to be very difficult to adequately replete their K+. If you are interested in the detailed mechanism of why that is, this paper gives a good description: https://jasn.asnjournals.org/content/18/10/2649. (In brief, one of the major mechanisms has to do with the fact that Mg++ is an important determinant of K+ secretion vs reabsorption in the distal nephron because intracellular Mg++ blocks channels responsible for K+ secretion; low Mg++ unblocks the channels and allows for increased K excretion).

There are two main reasons that I give IV Mg++ when I am trying to rapidly increase Mg++ serum concentrations in DKA to support my K+ repletion:

1) The IV route of Mg++ administration seems to result in a larger and more rapid increase in the serum Mg++ concentration (Am J Health Syst Pharm. 2012 Jul 15;69(14):1212-7). You can give IV Mg++ pretty quickly (for example, in asthma exacerbations, most protocols give 2gm over 20 minutes), meaning you are not tying up one of your IV lines for hours while the Mg++ is infusing.

2) These patients are often nauseous and vomiting. In a patient with a good mental status, I will still try to give them lots of ondansetron and see if I can get them to participate in some PO electrolyte repletion, HOWEVER if they are already nauseous I want to minimize the number of pills I am asking them to swallow. And I am prioritizing PO intake of K+ over Mg++ because K+ takes FOREVER to replete IV (most hospitals set upper limits at 10mEq per hour via a peripheral IV and 20mEq/hr via a central line), and so if your patient can tolerate it, it can be much faster to replete the K+ PO. In practice, I usually start PO and IV K+ at the same time in case the patient does start throwing up after I give them the PO K+ (also most people can only take 40-60mEq of K+ at a time before they start feeling pretty nauseous).

Hope that helps!