Hyponatremia

What is a normal sodium level? what is hyponatremia? what is hypernatremia?

normal: 135-145

hypo: less then 135

hyper: greater then 145

Who are the at risk populations for hyponatremia?

ICU pts, postop pts, psych, elderly (esp. nursing home pts)

What recreational drug has been shown to cause acute hyponatremia?

MDMA (molly, ecstasy)

With lab tests for hyponatremia, what order do we usually look in?

serum osmolality

urine osmolality

urine sodium

What is hyponatremia with a high plasma osmolality?

hyperglycemia and mannitol (aka factitious hyponatremia)

explain factitious hyponatremia with hyperglycemia and mannitol

they pull water out of the cells into the blood vessels

so the sodium levels are normal but they seem low because the excess water is diluting it

What goes with hyponatremia and a normal plasma osmolality?

“pseudohyponatremia”

hyperproteinemia, hyperlipidemia, or s/p bladder irrigation

explain pseudohyponatremia with hyperproteinemia, hyperlipidemia, and bladder irrigation

Pseudohyponatremia happens when the salt-to-water ratio in the body is actually normal, but the lab result looks low because extra lipids or proteins take up space in the plasma

When we have hyponatremia and a low plasma osmolality, what do we think?

we think that is those are both low, what does the urine osmolality look like

what do we suspect if we have hyponatremia, low plasma osmolality, and low urine osmolality (dilute urine)?

primary polydipsia (drinking too much water)

What do we suspect if we have hyponatremia, low serum osmolality, and high urine osmolality?

we need to then look at ECF volume status

What do we suspect if we have hyponatremia, low serum osmolality, high urine osmolality, and increased ECF volume?

CHF, cirrhosis, nephrotic syndrome, and renal insufficiency

What do we suspect with hyponatremia, low serum osmolality, high urine osmolality, and normal ECF?

SIADH, hypothyroidism, or adrenal insufficiency

What do we suspect with hyponatremia, low serum osmolality, high urine osmolality, and decreased ECF volume?

we have to look at urine sodium

What do we suspect with hyponatremia, low serum osmolality, high urine osmolality, and decreased ECF volume, and urine sodium <20?

extrarenal loss, secretory diarrhea, insensible loss (sweating, burns, etc.)

What do we suspect with hyponatremia, low serum osmolality, high urine osmolality, decreased ECF volume, and urine sodium >20?

sodium wasting nephropathy, hypoaldosteronism, and diuretic use

with acute hyponatremia, what is the ECF vs ICF?

what occurs with this?

ECF: hypotonic (lots of water and lower solute)

ICF: hypertonic (less water and higher solute)

so water gets drawn in to the cells

acute hyponatremia can lead to cerebral ____

cerebral edema

the brain cells can pump out the osmoles into the ECF to adapt to ____

cerebral edema (likely from hyponatremia)

explain aggressive therapy with cerebral edema and adaptation

the brain cells can adapt on their own to combat cerebral edema, so if you do too aggressive of a therapy then this can actually draw water out of the brain cells (osmotic demyelination)

what can occur with overly aggressive therapy to treat cerebral edema (especially if the brain has started adaptation)

osmotic demyelination (water drawn out of brain cells)

What part of the brain is mostly affected by osmotic demyelination?

pons

What are 3 things we commonly see with osmotic demyelination?

quadriparesis, diplopia, and loss of consciousness

hospital vs outpatient? what is the setting of treatment for the different levels of hyponatremia?

mild hyponatremia or asymptomatic moderate hyponatremia: outpatient

severe hyponatremia or symptomatic moderate: hospital

What is the goal when treating hyponatremia?

raise sodium 4-6 meq/L in 24 hours

do NOT correct more then 10 in 24 hours

same as with hypernatremia

What is the treatment for SIADH?

fluid restriction

combines salt tablets and furosemide (loop diuretic)

vasopressin receptor antagonists