Sodium: Hypernatremia and Hyponatremia

Question 1

What is normal serum sodium?

Answer 1

135-140 meq/l

Question 2

What is the equation for eximating plasma osmolality? and what is the biggest contributor to that osmolality?

Answer 2

Nax2 + BUN/2.8 + Glucose/18

Sodium is the biggest contributor

Question 3

Hypo and hypernatremia are almost always ____ problems, not salt problems/

Answer 3

water problems

Question 4

What are the symptoms of hyponatremia?

Answer 4

All due to brain cell swelling….

Na+ < 115 meq/liter: obtundation, seizures, coma

Question 5

When will symptoms be worse: gradual decrease in Na or sudden increase in Na?

Answer 5

the sudden increase will have worse symptoms because the brain can learn to compensate for the gradual increases

Question 6

What are the symptoms of hypernatremia due to? What are they?

Answer 6

the extracellular hyperosmolality causes brain cells to dehydrate - sometimes the vessels can even rupture

lethargy, weakness, irritability, twitching, seizures, coma, death

Question 7

What hormone will be released during times of hypernatremia?

Answer 7

ADH - increases water reabsorption to hopefully dilute out the sodium

Question 8

If ADH is present, urine osmolality will be ____.

If ADH is absent, urine osmolality will be ____.

Answer 8

high - H20 is being brought back in to the body as expense of urine
low - H20 remains in the tubule to dilute the solutes

Question 9

if urine osmolality tells us whether ADH is present or not, what does urine sodium tell us?

Answer 9

tells us what the kidney thinks about the volume status….
high urine Na = thnks body volume is expanded - getting rid of excess
low urine Na = thinks volume is depleted, reclaiming sodium

Question 10

Remember the equation Na+
Na x 2 + glucose/18 + BUN/2.8

Why doesn’t BUN contribute much?

Answer 10

urea can cross membranes, so it’s an ineffective osmole

Question 11

What is pseudohyponatremia?

Answer 11

hyponatremia with normal or elevated plasma osmolarity

Question 12

Hyponatremia with normal Posm is usually related to what> Hyponatremia with elevated Posm is usually related to what?

Answer 12

normal Posm = hyperlipidemia or hyperproteinemia (they take up more plasma space and reduce plasma water space but Na is still measured in total plasma space)

elevated = hyperglycemia, mannitol (osmotic diuresis so Na is more dilute)

Question 13

How can hyponatremia develop if there are mechanisms to maintain plasma osmolarity within 1%?

Answer 13

there are NON-OSMOTIC stimuli that will trigger ADH release, which work to maintain effective circulating volume at the expense of plasma osmolarity

Question 14

What are the clinical steps for evaluating hyponatremia?

Answer 14

1. check Posm - true hypoosmolar hyponatremia?
2. check urinary osmolarity to see if ADH is acting
3. Check urinary sodium to see kidney’s perception of ECV
4. check patient and H&P

Question 15

What should you ask about in the history? What should you look for on exam?

Answer 15

ask about volume losses, medications, pain, surgery

physical exam for volume status - JVD, edema, rales, S3, etc.

Question 16

Hyponatremia with Uosm less than 100 is almost always due to what?

Answer 16

it means ADH is not being produced due to apprpriate response to hypoosmolarity and the body wants to get rid of water appropriately

almost always due to polydipsia

Question 17

How many liters of water do you need to drink daily to overwhelm the renal capacity to clear water and cause hyponatremia? Exceptions?

Answer 17

10-15liters

unless ins beer potomania and tea/toast syndrome

Question 18

What is the treatment for polydipsia?

Answer 18

just fluid restrict! the body will quickly get rid of the water since no ADH is present

Question 19

Explain wha tis happening in terms of ADH when you have hyponatrmia with Uosm over 100.

Answer 19

THe urine is more concentrated because ADH is present

but your’e hypoosmolar! This means the ADH must be being secreted in respnose to some other stimuli because ECV is low

Question 20

What are common causes of hyponatremia with UNa+ less than 10 in volume depletion?

Answer 20

volume depletion:

Gi losses, burns, diuretics, pure cortisol deficiency

Question 21

What are common causes of hyponatremia with UNa less than 10 when the volume is expanded but the kidneys perceive ECV depletion?

Answer 21

kidneys being fooled by edematous states or poor perfusion (CHF, dirrhosis, nephrotic syndrome)

Question 22

What are the common causes of hyponatremia with UNa over 10 with volume depletion?

Answer 22

salt wasting!
adrenal insufficiency, salt wasting renal diseases, diuretics, hypokalemia with metabolic alkalosis after vomiting (loss of Na with bicarbonate loss), hypothyroidism

Question 23

What are common causes of hypoNa with UNa over 10 when the volume is appropriate or expanded?

Answer 23

Excess ADH production!

SIADH, a reset osmostat from trauma, or chornic kidney disease

Question 24

How do you treat SIADH?

Answer 24

fluid restrict
increase osmolar load - high intake of sodium or high protein (just to give them more room to work with and drink a little more fluid)

Question 25

What should the rate of hypoNa correction be? Why so slow?

Answer 25

0/5 meq/liter/hour

rapid correction has risk fo central pontine myelinolysis (osmotic demyelination syndrome) - more risk if the hypoN developed gradually

Question 26

What should you give the patient in emergency if they’re having neurological problems from severe hypoNa?

Answer 26

3% saline to replace the serum sodium quickly and get them out of danger

Question 27

What drugs can you give in hypervolemic hyponatremia?

Answer 27

an ADH antagonist - the “vaptans” to block the inappropriate reabsorption of whater

Question 28

In general, what is the cause of hyperNa?

Answer 28

excess water losses or inadequate intake

we’re usually protected form this by thirst, so seen mostly in the young, elderly, or mentally incapable to accessing water

Question 29

If Na is over 145, then Posm will be over 290. What should Uosm be and why?

Answer 29

UOsm should be way over 100 - like 800-1400 because ADH release should be maximal

Question 30

If Uosm is over 800 when Posm is over 290 (appropriately) what is the cause of the hyperNa?

Answer 30

primary hypodipsia
increased insensible GI losses
Na overload

Question 31

If Uosm is less than 300 when Posm is over 290, what is the cause?

Answer 31

central diabetes insipidus or nephrogenis diabetes insipidus

note - anything Uosm between 300-800 will be partial diabetes inspidus or osmotic diuresis

Question 32

How can you differentiate between central and nephrogenic DI?

Answer 32

give exogenous ADH and see what happens to Uosm.

if it’s central, the ADH will work and Uosm will increase as water is reabsorbed

If it’s nephrogenic the ADH won’t work and Uosm will remain low

Question 33

What drug did Dr. Popham harp on for nephrogenic DI?

Answer 33

lithium

Question 34

What is the treatment for diabetes insipidus?

Answer 34

need to diminish the polyuria/polydipsia

low Na diet and thiazide diuretic (counterintuitive, but it induces mild volume depletion and can thus decrease urine output)

moderate protein restriction to decrease osmolar load and therefore minimize amount of free water that can be cleared

or just give ADH for central diabetes insipidus

Question 35

What will the brain develop in chronic hypernatremia?

Answer 35

idiogenic osmoles to prevent cellular dehydration

Question 36

Again, what is the safe rate of sodium correction?

Answer 36

0.5 meq/l/hr

or 12 meq in a day

Question 37

How do you calculate someone’s free water deficit in hypernatremia?

Answer 37

men usually are 60% water and women are usually 50% water. If they’re dehydrated you can expect they’re 10% less than they would otherwise be.

So take body weight and multiply by 50% for men and 40% for women

then multiply it by the serum [Na} over 140) minus 1

Question 38

How quickly should you replace the free fluid deficit?

Answer 38

over about 60 hours

Question 39

What should the fluid composition be in treating hypernatremia?

Answer 39

1. free water orally or D5W IV
2. 1/4 NaCl saline fro hypernatremia due to volume depletion
3. normal saline if hypotensive with fluid losses