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 serum Na+  



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Author12 Posts
  #1

Increase in plasma levels of glucose as occurs in diabetic ketoacidosis result in hyponatremia along with increase in serum osmolality; however an increase in BUN also causes increase in serum osmolality but have no effect on serum Na+ concentration! WHY?




  #2

in diabetes,the patient has polyuria so he may loose more of Na+ in urine.

??



  #3

no, try again confused





  #4

glucose is a non-permeant solute therefore increases in ECF glucose will increase the serum osmolality (as in diabetic ketoacidosis) ,which will create an osmotic gradient across the membrane and will cause a fluid shift from ICF to ECF resulting in cellular dehydration as well as dilutional hyponatremia!

urea is a premeant solute which if elevated in the plasma will increase the osmolality of all compartments proportionally, therefore no osmotic gradient is created and no effect whtsoever on Na+ conc.!



  #5

oh,that was simple i just overlooked it


  #6

ssrpk wrote:
glucose is a non-permeant solute therefore increases in ECF glucose will increase the serum osmolality (as in diabetic ketoacidosis) ,which will create an osmotic gradient across the membrane and will cause a fluid shift from ICF to ECF resulting in cellular dehydration as well as dilutional hyponatremia!

urea is a premeant solute which if elevated in the plasma will increase the osmolality of all compartments proportionally, therefore no osmotic gradient is created and no effect whtsoever on Na+ conc.!



in diabetic ketoacidosis, ICF shift to ECF, but ECF decrease instead of increasing because they are lost in urine.

are you sure ECF increase in ketoacidosis and enough to dilute the sodium?



  #7

hey ofcourse u are right, about the contraction of over all plasma volume due to loss in the urine!

sodium dilution occurs because of relative excess of H2O when compared to sodium! [more Na loss than water]



  #8

What do you think of the correction, that you have to make to calculate the real serum sodium. I think you know that you have to apply a correction to Lab value.

Because, in DKA you have polyuria, and the lab serum sodium is falsely elevated( due to net loss of water in the urine, due to the water going out with the glucose that is being excreted in the urine). So the lab shows a false hypernatremia, but actually it is dilutional hyponatremia.

If you know tell me what is the correction factor?



  #9

well tubular fluid flow will increase in the face of KA resulting in polyuria which indeed is due to the osmotic effects of glucose but realize that Na+ will be dragged along with the fluid as Na+ reabsorption is dependent on Na+ conc. rather than the amount!

i don't think labs will be shwoing any hypernatremia if u use the relation of serum Na+ = TBNa+/TBW;but i'l look into this correction factor ,not sure abt it!

thnx for pointing out!



  #10

I know, you also lose Na with the water that is being excreted in the urine( due to the osmotic effect of glucose), but you still lose more water than Na( losing hypotonic fluid) and applying the same relation of Serum Na, you still get a hypernatremia on labs.

This concept should not be that emphasised on Step 1, but could be a part of Step 2, I think!!

What do you think?



  #11

there's wht i found in ganong!

In ketoacidosis, Na+ and K+ loss adds to dehydration because they are excreted along with the organic anions (ketones mainly) not covered by H+/NH+ excretion by the kidney.

secondly it also states tht in KA glucose becomes the major factor tht determines osmolality of plasma a/a urine, so i highly doubt this hyprenatremia thing, maybe a/s with some other condition.

now the correction factor for calculating this plasma osmolality in case of hyperglycemia is:

corrected serum Na+ = serum Na+ + (glucose[mg/dL]/100 X 1.6) {rapid review}



  #12

Thanks for the correction factor.

I am also trying to find out. This concept was actually pointed out by a friend.






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