Flashcards in Hypernatremia Deck (33):
Review: Formula for plasma osmolality?
2*Na + Glucose/18 + BUN/2.8
Review: Formula for calculated plasma tonicity?
2*Na + Glucose/18
2 "basic characteristics" of hypernatremia?
Increase in plasma concentration of at least 1 effective solute.
Decreased in ICF volume.
Can hypertonicity cause intracrancial hemorrhage?
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?
(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)
3 types of causes of euvolemic hypernatremia?
Extra-renal (insensible water loss).
Renal water loss.
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)
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 = 0.6*weight for men, 0.5*weight 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?
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.
Treatment for hypervolemic hypernatremia?
Treat the volume first to protect breathing: diuretics, extracorporeal ultrafiltration (just... mechanically removing vascular volume), ventilation.
Then, when volume is reduced, give D5W to address tonicity.
As a general rule, if someone has a problem with both volume and tonicity, which should you treat first?
Get the volume under control first (if you can't do both at the same time).
How high does glucose get in hyperosmotic hyperglycemic non-ketosis (HHNK)?
Really really high. Typically over 500 mg/dL.
3 phases of HHNK?
1: Hyperglycemia (ECF expansion, dilution of Na+)
2: Osmotic diuresis
3: H2O and Na+ loss -> reduced ECF volume, hypernatremia.
What are serum [Na+] levels like in HHNK?
Depends on the phase of the disorder.
Early, it's low because hyperglycemia draws water into ECF and dilutes the plasma.
Later, as water is lost through osmotic diuresis, [Na+] increases.
If you see somebody with a blood glucose of 1800mg/dL, you should think, "Oh shit, get them some insulin right now." ...right?
Wrong. If they have HHNK (which they probably do if the glucose is that high), that glucose could be the only this sustaining their vascular volume.
Giving insulin could put them into hypovolemic shock.
Treatment for HHNK?
Saline to get the volume up, then insulin to bring down the hypoglycemia.
(and address the cause the precipitated the hyperglycemia, if possible)
This wasn't emphasized in lecture, but why do you also need to give K+ when treating HHNK?
Insulin will draw K+ into cells - so if you don't replace it, K+ can drop dangerously low.
(same applies for treating diabetic ketoacidosis)