Sodium: Hypernatremia and Hyponatremia Flashcards
What is normal serum sodium?
135-140 meq/l
What is the equation for eximating plasma osmolality? and what is the biggest contributor to that osmolality?
Nax2 + BUN/2.8 + Glucose/18
Sodium is the biggest contributor
Hypo and hypernatremia are almost always ____ problems, not salt problems/
water problems
What are the symptoms of hyponatremia?
All due to brain cell swelling….
Na+ < 115 meq/liter: obtundation, seizures, coma
When will symptoms be worse: gradual decrease in Na or sudden increase in Na?
the sudden increase will have worse symptoms because the brain can learn to compensate for the gradual increases
What are the symptoms of hypernatremia due to? What are they?
the extracellular hyperosmolality causes brain cells to dehydrate - sometimes the vessels can even rupture
lethargy, weakness, irritability, twitching, seizures, coma, death
What hormone will be released during times of hypernatremia?
ADH - increases water reabsorption to hopefully dilute out the sodium
If ADH is present, urine osmolality will be ____.
If ADH is absent, urine osmolality will be ____.
high - H20 is being brought back in to the body as expense of urine
low - H20 remains in the tubule to dilute the solutes
if urine osmolality tells us whether ADH is present or not, what does urine sodium tell us?
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
Remember the equation Na+
Na x 2 + glucose/18 + BUN/2.8
Why doesn’t BUN contribute much?
urea can cross membranes, so it’s an ineffective osmole
What is pseudohyponatremia?
hyponatremia with normal or elevated plasma osmolarity
Hyponatremia with normal Posm is usually related to what> Hyponatremia with elevated Posm is usually related to what?
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)
How can hyponatremia develop if there are mechanisms to maintain plasma osmolarity within 1%?
there are NON-OSMOTIC stimuli that will trigger ADH release, which work to maintain effective circulating volume at the expense of plasma osmolarity
What are the clinical steps for evaluating hyponatremia?
- check Posm - true hypoosmolar hyponatremia?
- check urinary osmolarity to see if ADH is acting
- Check urinary sodium to see kidney’s perception of ECV
- check patient and H&P
What should you ask about in the history? What should you look for on exam?
ask about volume losses, medications, pain, surgery
physical exam for volume status - JVD, edema, rales, S3, etc.
Hyponatremia with Uosm less than 100 is almost always due to what?
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
How many liters of water do you need to drink daily to overwhelm the renal capacity to clear water and cause hyponatremia? Exceptions?
10-15liters
unless ins beer potomania and tea/toast syndrome
What is the treatment for polydipsia?
just fluid restrict! the body will quickly get rid of the water since no ADH is present
Explain wha tis happening in terms of ADH when you have hyponatrmia with Uosm over 100.
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
What are common causes of hyponatremia with UNa+ less than 10 in volume depletion?
volume depletion:
Gi losses, burns, diuretics, pure cortisol deficiency
What are common causes of hyponatremia with UNa less than 10 when the volume is expanded but the kidneys perceive ECV depletion?
kidneys being fooled by edematous states or poor perfusion (CHF, dirrhosis, nephrotic syndrome)
What are the common causes of hyponatremia with UNa over 10 with volume depletion?
salt wasting!
adrenal insufficiency, salt wasting renal diseases, diuretics, hypokalemia with metabolic alkalosis after vomiting (loss of Na with bicarbonate loss), hypothyroidism
What are common causes of hypoNa with UNa over 10 when the volume is appropriate or expanded?
Excess ADH production!
SIADH, a reset osmostat from trauma, or chornic kidney disease
How do you treat SIADH?
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)
