Hypernatremia Flashcards
Review: Formula for calculated plasma tonicity?
2*Na + Glucose/18
Review: Formula for plasma osmolality?
2*Na + Glucose/18 + BUN/2.8
2 “basic characteristics” of hypernatremia?
Increase in plasma concentration of at least 1 effective solute.
Decreased in ICF volume.
Can hypertonicity cause intracrancial hemorrhage?
Yup.
Why doesn’t the brain shrink as much as one might expect in hypernatremia?
Organic osmolytes are produced.
it’s unclear whether this is a defensive mechanism, or a sign of damage
Are changes in brain volume more rapidly revered in hypernatremia or hyperglycemia?
More rapidly reversed in hyperglycemia.
2 physiologic responses to hypertonicity?
ADH release.
Thirst.
(both trying to increase water)
Review: What’s the best way to determine someone’s total body Na+ content?
Physical exam to determine volume status.
What will happen if you lose free water and don’t replace it? (in terms of volume and tonicity)
Euvolemic hypernatremia.
3 types of causes of euvolemic hypernatremia?
Extra-renal (insensible water loss).
Renal water loss.
Primary hypodipsia.
2 types of renal water loss that can cause euvolemic hypernatremia?
Central diabetes insipidus (inadequate AVP).
Nephrogenic diabetes insipidus (AVP resistance).
For every liter of free water that you lose, about how much would lost from the vasculature?
What significance have for a person’s volume status?
only about 83 ml.
This is why water loss / inadequate water intake results in euvolemic hypernatremia, not hypovolemic hypernatremia.
What lab values can you use to determine if euvolemic hypernatremia has a renal cause? (i.e. inadequate water retention)
Urine osmolality.
If urine is inappropriately dilute (< 100mOsm), it’s a problem with ADH (not enough, or not responding to it).
If urine is concentrated, there has been inadequate water intake or excessive insensible loss.
What formula can you rearrange to determine the total body water (TBW) deficit in somebody with euvolemic hypernatremia?
Normal TBW * Normal Plasma Na = Current TBW * Current Plasma Na.
(TBW = 0.6weight for men, 0.5weight for women.)
Solve for Current TBW, then subtract Normal - Current TBW to find the deficit.
Treatment for euvolemic hypernatremia?
How fast should you go?
Oral water, or IV D5W.
Only correct 50% in the first 24-48 hours to avoid cerebral edema.
What’s the problem in hypovolemic hypernatremia?
Both water and Na+ are lost, but more water than Na+ is lost.
This is often exacerbated by inadequate water intake.
2 broad categories of causes of hypovolemic hyponatremia?
Renal causes (diuresis) Extra-renal causes (water and Na+ loss)
2 renal causes of hypovolemic hypernatremia?
Diuretics (iatrogenic). Osmotic diuresis (too much glucose or urea).
2 organ systems through which one can lose both water and Na+ to cause hypovolemic hypernatremia?
GI (diarrhea, vomiting, NG suction).
Skin (profuse sweating, extensive burns).
In contrast to losing in a liter of free water, if you lose 1 liter of iso-osmotic saline, how much plasma volume will be lost?
250ml of plasma will be lost. (in contrast to just 83ml with free water)
Almost all the 1000ml will be lost from the ECF.
How can lab values help you determine if hypovolemic hypernatremia has a renal or extra-renal cause? (you should notice a pattern here)
High volumes of inappropriately dilute urine: renal cause.
Low volumes of concentrated urine: extra-renal cause.
Treatment for hypovolemic hypernatremia?
this is one of the most intuitive treatments, given the cause
Give saline (slowly!)
They’ve lost volume, so they need salt.
They’ve lost water, so they need water.
What causes hypervolemic hypernatremia?
Isolated sodium excess. (most commonly iatrogenic)
3 causes of hypervolemic hypernatremia?
Hypertonic saline (iatrogenic).
Infant salt poisoning.
Sea water ingestion.
