Sodium and water balance Flashcards
sodium disorders are almost always caused by disorders of ____________
water (im)balance
lab value: hyponatremia
[Na} under 135 mmol / L
what are the CNS symptoms of hyponatremia?
- N/V
- headache
- fatigue
- WEAKNESS
- seizure
- coma
- death
the severity of the hyponatremia symptoms is related to what factors?
- rapidity
- severity
lab value: severe hyponatremia
[Na} under 120 mmol/L
what level of [Na] indicates an absolute requirement to treat?
[Na} under 120 mmol/L (severe hyponatremia)
what is the concept of osmotic adaptation?
- brain cells can produce or excrete osmols in order to protect against cellular dehydration or over hydration
how does the concept of osmotic adaptation relate to hypo-osmotic states? hyperosmotic?
- hypo-osmotic states: brain cells adapt initially by excreting intracellular osmols; thereby reducing the risk of cellular overhydration
- hyperosmotic states: brain cells adapt by producing intracellular osmols in an effort to prevent cellular dehydration
what is osmotic demyelination syndrome?
process of demyelination of the central nervous system
what are the characteristics of central pontine myelinolysis? how does it occur?
- paraparesis
- dysarthria
- dysphagia
- seizure
- coma
- death
- occurs by overly rapid correction of hyponatremia
what is the relationship of primary polydipsia and hyponatremia?
disorder with normal water excretion (uncommon) - primary polydipsia (excessive water intake that overwhelms kidney ability to excrete water load)
what is pseudohyponatremia?
- in states of severe hyperlipidemia or hyperproteinemia, the fraction of plasma water may be reduced
- lab measured serum sodium may be artifactually lower as this is measured as a liter of total plasma - not just plasma water
what are the HYPOvolemic causes of hyponatremia / hypo-osmolality (renal and extra-renal)?
- renal losses: diuretics, osmotic diuresis
- extra-renal losses: blood loss, diarrhea / vomiting
what are the HYPERvolemic causes of hyponatremia / hypo-osmolality?
- renal failure: increased urinary sodium
- CHF, cirrhosis, nephrotic syndrome: increased ECF by decreased effective circulating volume (decreased urinary sodium, higher urinary osmolarity)
what are the EUvolemic causes of hyponatremia / hypo-osmolality?
- hypoadrenalism / hypothyroidism: increased ADH
- SIADH: elevated ADH
how does hypoadrenalism cause hyponatremia / hypo-osmolarity?
- cortisol directly inhibits ADH secretion
- low BP in hypoadrenalism stimulates ADH secretion
- CRH mimics ADH function
how does hypothyroidism cause hyponatremia / hypo-osmolarity?
thyroid hormone inhibits ADH
what is the mechanism for why SIADH causes hyponatremia / hypo-osmolarity?
- urine osmolarity is inappropriately elevated [concentrated] for the hyponatremic state
- urine is NOT maximally dilute as it should be
what is the 1) edema state and 2) volume expansion status in SIADH / hyponatremia?
- no edema
- very modest volume expansion
what are the serum uric acid and BUN levels for SIADH / hyponatremia?
commonly low serum uric acid and BUN
what are the diagnostic characteristics for SIADH?
- hyponatremia and hypoosmolarity
- inappropriately elevated urine osmolarity
- normovolemic on clinical exam (no edema)
- normal renal / adrenal / thyroid function
what is the treatment for pseudohyponatremia?
underlying causes:
- hyperlipidemia or
- myeloma
what is the treatment for true hyponatremia?
- raise serum sodium by a safe rate
- 0.9 NS for volume depletion
- restrict free water intake for euvolemia or hypervolemia
- demeclocycline
- vasopressin antagonists
what is the treatment for severe hyponatremia?
consider hypertonic 3% saline
what is the role of demeclocycline for true hyponatremia?
increases urinary water loss
what is the role of vasopressin antagonists for true hyponatremia?
increases urinary water loss
hypernatremia results from what 3 factors?
- water loss
- sodium retention (rare)
- water loss in excess of sodium loss
how do you combat hypernatremia?
stimulate ADH production
how does hypernatremia persist?
inability to access water and/or inability of the kidne to appropriately reabsorb water
what are the causes of diabetes insipidus? what is the result?
- ADH production or secretion (central)
- renal response to ADH (nephrogenic)
- RESULT: reduction in water reabsorption by the kidney and a diuresis of dilute urine leading to hypernatremia
what is the hypothalamic function and ADH release status in nephrogenic DI?
normal
what are the etiologies of NDI?
- congenital
- hypercalcemia
- hypokalemia
- drugs (lithium, demeclocycline)
- renal parenchymal disease
what drugs cause NDI?
- lithium
- demeclocycline
does primary polydipsia cause hypernatremia or hyponatremia?
hyponatremia
how do you differentiate between NDI/CDI and primary polydipsia?
water deprivation test
following a water deprivation test, in what condition will you see a change of urine osmolarity after administering ADH? what is this change?
CDI (increase)
when is treatment indicated for hypernatremia?
- symptomatic
- volume depleted
- hypernatremia is severe
