SIADH, DI, Cerebral Salt
Wasting
By Tracy Merrill MD
Feb 24, 2003
SIADH:
• = Syndrome of Inappropriate ADH
Secretion
• Definition: levels of ADH are
inappropriately elevated compared to
body’s low osmolality, and ADH levels are
not suppressed by further decreases in
blood osmolality.
SIADH: causes
• Irritation of CNS: meningitis, encephalitis,
brain tumors, brain hemorrhage, hypoxic
insult, trauma, brain abscess, Guillain
Barre, hydrocephalus
• Pulmonary disorders: pneumonia,
asthma, positive end expiratory pressure
ventilation, CF, TB, pneumothorax
SIADH: causes continued
• Drugs: vincristine, vinblastine, opiates,
carbamazepime, cyclophosphamide
• Unregulated tumor production of ADH-like
peptides: oat cell lung carcinoma for
example, Ewings sarcoma, carcinoma of
duodenum, pancreas, thymus
SIADH: function of ADH
• = antidiuretic hormone = vasopressin
• ADH is made in the supra-optic nuclei in the
•
•
•
hypothalamus, stored in the posterior pituitary
Normally released into the bloodstream when
osmo-receptors detect high plasma osmolality
At the kidney, attaches to receptors in the
collecting ducts, opens up water channels
Water is passively reabsorbed along the kidney’s
medullary concentration gradient
SIADH: signs and symptoms
• Decreased/low urine output
• Signs of hyponatremia: lethargy, apathy,
disorientation, muscle cramps, anorexia,
agitation
• Signs of water toxicity: nausea, vomiting,
personality changes, confused, combative
• If Na < 110 mEq/L, seizures, bulbar
palsies, hypothermia, stupor, coma
SIADH: lab values
• Serum Na < 135 (Na is diluted by excessive
•
•
•
•
free water re-absorption)
Serum osmolality low, normal is ~ 270
Urine Na is inappropriately high, >20 mmol/L,
actually losing Na in urine instead of retaining it
Urine osmolality is inappropriately high, can
range b/t 300-1400 mosm/L
CVP is high from free water retention
SIADH: treatment
• Fluid restriction, ¾ maintenance
• If symptomatic, may actually need to
replace NaCl, can use hypertonic saline for
example: 300cc/m2 of 1 ½ % NS
• Diuretics such as lasix
• Treat underlying disorder, for example
usually resolves after removal of lung
carcinomas
SIADH: treatment cont…
• Demeclochlorotetracycline, blocks ADH
receptors in the renal collecting ducts
• In severe cases, hemodialysis
• Warning, if increase Na too fast, at risk for
pontine myelinolysis
• Max correction of 15mEq in 24 hours
DI = Diabetes Insipidus
• Definition: inability to effectively conserve
•
•
urinary water
Central: ADH not made or not released in the
hypothalamic-pituitary axis
Nephrogenic: ADH is released but not detected
by the receptors in the kidney collecting ducts,
often a sex-linked recessive condition, also due
to renal pathology, electrolyte disorders, drugs
Central DI: causes
• Head trauma
• Brain neoplasms
• Congenital CNS defects
• CNS infections
• CNS hypoxia
• ADH secretion also decreased by certain
drugs: EtOh, demerol, MSO4, dilantin,
barbiturates, glucocorticoids
DI:
• Make sure distinguish DI from conditions in
•
which the presence of non-absorbable,
osmotically active solutes in the renal tubules
prevent water re-absorption.
Example: glucose loss in the urine of diabetics
will decrease the tubule- medullary
concentration gradient and even though ADH is
there, water won’t get passively reabsorbed
Central DI: signs/symptoms
• Polyuria
• Dehydration, may not be readily apparent
b/c of hyper-osmolarity, fluid shifts from
cells to intravascular spaces and maintains
blood pressure, CVP
• Weight loss is a better measure of fluid
status
Central DI: Lab values
• Hypernatremia, Na >150-160
• High serum osmolality (normal 270)
• Urine Na < 20 mmol/L
• Low urine osmolality (very dilute urine)
Central DI: treatment
• Increase po or IV free H20 consumption,
use hypotonic saline
• Volume replacement cc for cc
• Vasopressin/ ADH administration (bolus or
drip 1.5-2.5 mU/kg/hr)
• Of course, treat underlying cause
Cerebral Salt Wasting
• Causes: CNS damage
– Closed head injury
– CNS surgery
– CNS tumors
– CNS infections, meningitis
Cerebral Salt Wasting
• Signs/symptoms:
– Polyuria
– Wt loss
– Dehydration/hypovolemia
– Hypotension
– Low CVP
Cerebral Salt Wasting
• Lab values:
– Hyponatremia due to excessive renal Na loss
– High urine Na, > 20 mmol/L
– Increased plasma ANP, atrial natriuretic
peptide, b/c of low volume status
– Inappropriately normal or low aldosterone
and ADH levels despite high ANP
Cerebral Salt Wasting
• Treatment:
– Volume for volume replacement of urine Na
losses
– When dc’d from hospital, most will still need
oral Na supplementation for a period of time
DI
SIADH
CSW
Urine Output polyuric
decreased
polyuric
Serum Na
high
low
low
Urine Na
low
high
high
Serum osm
high
low
Can be low
or normal
Urine osm
low
high
Can be low
or normal
CVP
Can be
normal or
low
high
low