012915 posterior pit Flashcards
how is osmolality sensed?
by osmoreceptors in hypothalamus
turns on response if needed to cause posterior pituitary to secrete vasopressin
SIADH usually presents how?
SIADH usually has slow changes in terms of disease progression, so few symptoms may arise b/c the body compensates
what can cause SIADH?
lung disease
drugs
cerebral problems (multiple sclerosis, trauma, etc)
others (HIV, etc)
symptoms of SIADH?
fatigue
irritability
stupor
how do you diagnose SIADH?
if pt has hyponatremia, you measure serum osmolality.
if hypotonic serum osmolality (under 275 mOsm/L), you assess volume status.
if pt is euvolemic, measure urine osmolality.
if urine osmolality is under 100 mOsm/L, it’s water intoxication. if urine osmolality is over 100 mOsm/L, it’s either SIADH, or adrenal insufficiency, or hypothyroidism (you’d have to rule out latter two)
criteria for SIADH (a diagnosis of exclusion)
euvolemic
serum sodium and serum osmolality are low
urine osmolality is over 100 mM
urine sodium over 20 mEq/L
hypothyroidism and adrenal insufficiency have been ruled out
how to manage SIADH
1st: determine cause of SIADH
fluid restriction
IV salt solution (for acute correction)
if above initial txs are ineffective, there’s pharm:
- -vasopressin receptor antagonists (conivaptan, talvaptan)
- -loop diuretics (furosemide, bumetanide)-infrequently used
- -demeclocycline (rarely used)
diabetes insipidus
central (neurogenic): deficient production/release of AVP
nephrogenic: renal resistance to AVP
in diabetes insipidus, serum sodium is usually
elevated
lithium can cause
nephrogenic diabetes insipidus
how to differentiate psychogenic polydipsia from diabetes insipidus
psychogenic polydipsia would have low normal serum Na
symptoms of fatigue can be identical in
SIADH and diabetes insipidus
history of pt with diabetes insipidus
polyuria, getting up at night
usually has polydipsia
how to diagnose diabetes insipidus
if pt has hypernatremia:
assess volume status. if euvolemic (no edema), it can be renal losses or extrarenal losses.
if renal loss, could be diabetes insipidus
for pt with polyuria, how to determine if it’s DI?
if urine osmolality is under 300 mosm/kg, it’s a non-osmotic diuresis, so do a water restriction test.
if water restriction test shows plasma osmolality in normal range, it’s psychogenic polydipsia. if water restriction test shows urin osmolality is under 300 msom/kg and plasma osmolality is over 300 mosm/kg, it’s DI.
