Hypernatremia

Question 0

Review: Formula for calculated plasma tonicity?

Answer 0

2*Na + Glucose/18

Question 1

Review: Formula for plasma osmolality?

Answer 1

2*Na + Glucose/18 + BUN/2.8

Question 2

2 “basic characteristics” of hypernatremia?

Answer 2

Increase in plasma concentration of at least 1 effective solute.
Decreased in ICF volume.

Question 3

Can hypertonicity cause intracrancial hemorrhage?

Answer 3

Yup.

Question 4

Why doesn’t the brain shrink as much as one might expect in hypernatremia?

Answer 4

Organic osmolytes are produced.

it’s unclear whether this is a defensive mechanism, or a sign of damage

Question 5

Are changes in brain volume more rapidly revered in hypernatremia or hyperglycemia?

Answer 5

More rapidly reversed in hyperglycemia.

Question 6

2 physiologic responses to hypertonicity?

Answer 6

ADH release.
Thirst.
(both trying to increase water)

Question 7

Review: What’s the best way to determine someone’s total body Na+ content?

Answer 7

Physical exam to determine volume status.

Question 8

What will happen if you lose free water and don’t replace it? (in terms of volume and tonicity)

Answer 8

Euvolemic hypernatremia.

Question 9

3 types of causes of euvolemic hypernatremia?

Answer 9

Extra-renal (insensible water loss).
Renal water loss.
Primary hypodipsia.

Question 10

2 types of renal water loss that can cause euvolemic hypernatremia?

Answer 10

Central diabetes insipidus (inadequate AVP).

Nephrogenic diabetes insipidus (AVP resistance).

Question 11

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?

Answer 11

only about 83 ml.

This is why water loss / inadequate water intake results in euvolemic hypernatremia, not hypovolemic hypernatremia.

Question 12

What lab values can you use to determine if euvolemic hypernatremia has a renal cause? (i.e. inadequate water retention)

Answer 12

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.

Question 13

What formula can you rearrange to determine the total body water (TBW) deficit in somebody with euvolemic hypernatremia?

Answer 13

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.

Question 14

Treatment for euvolemic hypernatremia?

How fast should you go?

Answer 14

Oral water, or IV D5W.

Only correct 50% in the first 24-48 hours to avoid cerebral edema.

Question 15

What’s the problem in hypovolemic hypernatremia?

Answer 15

Both water and Na+ are lost, but more water than Na+ is lost.
This is often exacerbated by inadequate water intake.

Question 16

2 broad categories of causes of hypovolemic hyponatremia?

Answer 16

Renal causes (diuresis)
Extra-renal causes (water and Na+ loss)

Question 17

2 renal causes of hypovolemic hypernatremia?

Answer 17

Diuretics (iatrogenic).
Osmotic diuresis (too much glucose or urea).

Question 18

2 organ systems through which one can lose both water and Na+ to cause hypovolemic hypernatremia?

Answer 18

GI (diarrhea, vomiting, NG suction).

Skin (profuse sweating, extensive burns).

Question 19

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?

Answer 19

250ml of plasma will be lost. (in contrast to just 83ml with free water)
Almost all the 1000ml will be lost from the ECF.

Question 20

How can lab values help you determine if hypovolemic hypernatremia has a renal or extra-renal cause? (you should notice a pattern here)

Answer 20

High volumes of inappropriately dilute urine: renal cause.

Low volumes of concentrated urine: extra-renal cause.

Question 21

Treatment for hypovolemic hypernatremia?

this is one of the most intuitive treatments, given the cause

Answer 21

Give saline (slowly!)
They’ve lost volume, so they need salt.
They’ve lost water, so they need water.

Question 22

What causes hypervolemic hypernatremia?

Answer 22

Isolated sodium excess. (most commonly iatrogenic)

Question 23

3 causes of hypervolemic hypernatremia?

Answer 23

Hypertonic saline (iatrogenic).
Infant salt poisoning.
Sea water ingestion.

Question 24

Treatment for hypervolemic hypernatremia?

Answer 24

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.

Question 25

As a general rule, if someone has a problem with both volume and tonicity, which should you treat first?

Answer 25

Get the volume under control first (if you can’t do both at the same time).

Question 26

How high does glucose get in hyperosmotic hyperglycemic non-ketosis (HHNK)?

Answer 26

Really really high. Typically over 500 mg/dL.

Question 27

3 phases of HHNK?

Answer 27

1: Hyperglycemia (ECF expansion, dilution of Na+)
2: Osmotic diuresis
3: H2O and Na+ loss -> reduced ECF volume, hypernatremia.

Question 28

What are serum [Na+] levels like in HHNK?

Answer 28

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.

Question 29

If you see somebody with a blood glucose of 1800mg/dL, you should think, “Oh shit, get them some insulin right now.” …right?

Answer 29

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.

Question 30

Treatment for HHNK?

Answer 30

Saline to get the volume up, then insulin to bring down the hypoglycemia.
(and address the cause the precipitated the hyperglycemia, if possible)

Question 31

This wasn’t emphasized in lecture, but why do you also need to give K+ when treating HHNK?

Answer 31

Insulin will draw K+ into cells - so if you don’t replace it, K+ can drop dangerously low.
(same applies for treating diabetic ketoacidosis)

Question 32

When calculating the water deficit in HHNK, how must you adjust the “Current serum Na+” value?

Answer 32

Hyperglycemia is causing dilution of Na+, so you should adjust the serum Na+ value such that it is increased by 2.4mEq/L for ever 100mg/dL excess glucose is present.