DI/SIADH Flashcards
Define DI
Fluid imbalance– inability to retain fluid and lack of sugar in urine
excessive thirst and excretion of large amounts (>3L/day) of dilute urination (<300 mOsm/kg)
Define C-DI
decreased ADH released from PP causing polyuria, polydipsia, nocturia
where is the defect with C-DI
hypothalamus or PP not making enough ADH
where is the defect with N-DI
kidney (collecting tubules or loop of henle) unresponsive to ADH
expected labs with C-DI vs N-DI
Central labs: LOW BMP, UA and ADH
Nephrogenic labs: normal-high BMP, UA, ADH
Both: high serum osmo, low urine osmo, no response to water deprivation
what causes thirst in DI
elevated serum Na (increased Osmo) stimulates thirst to replace urinary water loss
sx of hyper-natremia
lethargy
weakness
edema
irritability
NM excitability
exogenous ADH can help with which type of DI
Central DI
expected result of fluid deprivation test in someone w/ DI
no response to water deprivation
Define N-DI
kidney resistant to ADH–> decreased ability to concentrate urine
polydipsia, polyuria, nocturia
3 must haves for SIADH diagnosis
hyponatremia (<135) with low serum Osm (<275)
urine Osm >100mOsm/kg
Also: normal thyroid, renal and adrenal fx and urine sodium >30
ADH levels in DI vs SIADH
DI has inadequate ADH
SIADH has excess ADH
SERUM vs Urine osmolarity in DI & SIADH
Serum: DI high (polyuria), SIADH low (oliguria)
Urine: DI low, SIADH high
serum sodium in SI vs SIADH
DI: hypernatremia
SIADH: hyponatremia
main treatment differences for DI vs SIADH
DI: desmopressin, HCTZ, chlopropamide
SIADH: fluid restriction
relationship between ADH levels and urine production
increase in ADH= water retention/decreased urine production
no ADH= water voided and higher sodium concentration
what is the most important physiologic stimulant of ADH
plasma osmolaLity
cycle of ADH & plasma osmolali
increased ADH–> increased reabsorption–> decreased plasma osmolality–> decreased ADH release–> increased plasma osmolality
clinical signs of DI
polyuria, polydipsia, nocturia
craving cold water
hypernatremia
dehydration
causes of central/neurogenic vs nephrogenic DI
central causes: pit or hypo thalamus damage from trauma or surgery, autoimmune, tumors, drugs, vascular
nephrogenic causes: renal d/o or lithium therapy, congenital, electrolyte d/o, sickle cell
what happens if someone can’t respond to thirst stimulation?
severe hypernatremia= increased mortality
diagnostic for DI
water deprivation test +/- serum ADH
vasopressin test (IM)
MRI to evaluate pituitary
what is the vasopressin test (IM)
give IM vasopressin to determine if central or nephrogenic DI
if urine output slows- Central Di
if it remains the same- Nephrogenic DI
first line tx in Central vs Nephrogenic DI
central tx: desmopressin
nephrogenic: Diuretics- amiloride
other treatments for C-DI
HCTZ diuretics–causes mild hypovolemia & proximal Na & H2O reabsorption (end result is less urine output
Chlorpropamide (2nd line)– causes partial release of ADH & can cause hypoglycemia
Carbamazepine– enhances response to ADH in partial C-DI
Clofibrate– can induce SIADH
which medication can reverse lithium effect
Amiloride (diuretic)
name the only other class of meds that can work on N-DI
NSAIDs– inhibits prostaglandin synthesis so it doesn’t antagonize ADH
Indomethacin > Ibuprofen
which gramulomatous disease can cause C-DI
sarcoid
what drugs can cause C-DI
alcohol
diphenylhydantoin (seizure med)
Sx of SIADH
nausea/vomiting, cramps
depressed mood, irritable
confusion, hallucinations
seizures, coma
edema/wt gain
conditions associated w/ SIADH
head trauma
malignant neoplasms (esp small cell lung CA)
pulmonary dz
CNS d/o
drugs
lab findings w/ SIADH
low plasma Na, low plasma Osm, high urine Osm d/t disproportionate solute excretion w/o water
tx for SIADH
fluid restriction (for chronic hyponatremia)- fluids 500ml less than output
hypertonic saline if severe CNS sx (emergencies)
also: vasopressin receptor antagonist or urea to increase solute load and increase water loss
how does desmopressin (DDAVP) work?
acts on collecting duct causing non suppressible ADH activity–> inability to excrete ingested water (hyponatremia)
monitor Na+ after starting the medication!
