vasopressin disorders Flashcards
contrast central and nephrogenic diabetes insipidus and their different treatments
Central Diabetes Insipidus (CDI):
Cause: Vasopressin (ADH) deficiency due to damage to the hypothalamus or posterior pituitary (e.g., brain injury, tumors).
Treatment:
- Desmopressin (DDAVP) (synthetic vasopressin).
- Adequate water intake
Nephrogenic Diabetes Insipidus (NDI):
Cause: Kidney resistance to vasopressin due to genetic mutations (e.g., V2 receptor), lithium toxicity, or hypercalcemia.
Treatment:
- Thiazide diuretics (reduce urine output).
- Low-sodium diet and NSAIDs (improve ADH action)
- Desmopressin - non-hereditary forms - can overcome relative resistance
aetiology central and nephrogenic diabetes insipidus
central:
reduced secretion ADH
hypo or pitu issue
most commonly idiopathic (not known) 30-50%
can occur secondary to many conditions
- tumours
- hypopituitaryism
- following neurosurgery
- trauma
infection - TB + meningitis
- sarcoidosis (enlargement of lymph nodes)
nephrogenic:
caused by resistance to the effects of ADH:
- inherited - x chromosome
- aquired - chronic lithium use and hypercalcaemia
what is meant by hypotonic polyuria?
- excretion of large volumes of dilute urine because kidneys cannot reabsorb water
- linked to deficiency or resistance to vasopressin
risk factors diabetes insipidus
modifiable:
chronic lithium use
non-modifiable:
hypercalcaemia
investigation diabetes insipidus 1st line
urine and serum osmolality
urine osmolality - low
serum osmolality - high
opposite in SIAD
gold standard investigation diabetes insipidus
water deprivation/desmopressin stimulation test
- deprive all fluids 8hrs before
- measure urine osmolality and administer desmopressin
- wait 8hrs + measure osmolality again
central (C for changes)
- initial urine osmolality - low
- 8hrs post desmopressin - high
nephrogen - (N for no changes)
- initial urine osmolality - low
- 8hrs post desmopressin - low
explain why theres changes in desomopressin test in central insipidus and not nephrogenic
the desmopressin is a synthetic version of vasopressin
in central when there is not enough vasopresin, the desmopressin replaces it and makes it normal and fucntion properly
in nephrogenic its because os a resistance to by adding more synthetic vasopressin (desmopressin) will not make a difference
desmorpressin levels in both types of diabetes insipidus and primary polydypsia
primary dolpdypsia:
- before - high
- after - high
central insipidus:
- before - low
- after - high
nephrogenic:
- before - low
- after - high
diabetes insipidus key presentation
polyuria and polydypsia
another word for central diabetes insipidus
cranial diabetets insepidus
primary polydypsia
ADH secretion and function normal but patient drinks an excessive amount of water leading to excessive urine production
hypotonic polyuria conditions and how they differ
central diabetes insipidus
- deficiency of vasopressin
nephrogenic diabetes insipidus
- resistance to ADH - V2 receptor - genetic or aquired
management of vasopressin deficiency (central diabetes insipidus)
treat any underlying condition
desmopressin – high activity at V2 receptor
tablets 100-600 micrograms/day
nasal spray 10-20 micrograms/day
injection 1-2 micrograms/day
dose adjusted to response on monitoring of serum sodium
management of vasopressin resistance (nephrogenic diabetes insipidus)
try and avoid precipitating drugs
congenital onset - very difficult
free access to water
- very high dose desmopressin
investigation of hypotonic polyuria
- serum Na > 135mmol/l - primary polydipsia (drinking more so urinating more)
- urine osmolality test - < 800
AT THIS POINT WE KNOW ITS VASOPRESSIN RELATED POLYURIA
copeptoin result > 21.4 = ADH resistance
copeptoin result < 21.4 = ADH deficiency
copeptoin - protein released along with ADH release - indicated amount of ADH release
Hyponatraemia
Too much vasopressin release when it should not be released:
main cause = Syndrome of Anti-Diuresis – SIAD
Causes of SIAD
- Central Nervous System Disorders
- Tumours
- respiratory causes
- drugs
Biochemical Severe serum sodium
< 125mmol/l
Signs and symptoms of hyponatraemia
Headache
Irritability
Nausea / vomiting
Mental slowing
Unstable gait / falls
Confusion / delirium
Disorientation
severe:
Stupor / coma
Convulsions
Respiratory arrest
what does hyponatreamia morbidity and treatment depend on
whether onset and duration of hyponatraemia is acute or chronic
Hyponatremia definition
low levels of sodium (Na⁺) in the blood, typically defined as a serum sodium concentration below 135 mEq/L.
SIAD definition
- excessive release of ADH
- main cause of hyponatraemia
excess water reabsorption ;leading to:
- inc total body water
- euvolemic hyponatraemia (low sodium - same body water)
Treatment for hyponatraemia secondary to SIADH (2)
- Asymptomatic/mild symptoms: Fluid restrict; vaptans (vasopressin antagonist)
- Severe symptoms: 3% hypertonic saline to concentrate blood
what are some concequences of water excess and a dec in ECF osmolality?
- Hyponatraemia
- Cerebral overhydration
- Headache
- Confusion
- Convulsions
SIAD - management
Diagnose and treat underlying condition
fluid restriction <1L/24 hour
sometimes demeclocycline/ tolvaptan (V2 receptor antagonist)
if Na+ <115 mmol/l AND fitting hypertonic N/Saline on ITU
<8mmol/l increase in Na+ per 24 hour if chronic
Potential risk of osmotic demyelination
Hypernatremia definition
- elevated sodium levels
- serum concentration >145 mEq/L
- occurs when body loses too much water or retains too much sodium
primary causes of hypernatremea
- dehydration
- inc urine loss - diabetes insipidus
- vomitting diarrhoea
- excess sodium intake
mild and moderate symptoms of hypernetropea.
mild
- thirst
- dry mouth
- weakness and fatigue
- inc urine output - diabetes insipidus
moderate to severe
- confusion
- seizures
- coma
- brain hemmorrhage
normal plasma and urine osmolality readings
plasma - 275–295 mOsm/kg
urine - 300-700mOsm/kg
SIAD investigations
Blood test:
Gives a serum sodium reading ->able to confirm hyponatraemia
Serum osmolality will be low (less than 280mOsm/Kg)
Urinary test:
Urine osmolality - high urine osmolality (>100mOsm/Kg)
Urine sodium - high urine sodium (water has been taken out -> high sodium comparatively)
NO 1 TEST DIAGNOSES
treatment flowchart SIAD
essential diagnostic criteria SIAD
complications of desmopressin
hyponatraemia due to water retention
SIAD aetiology
- post major procedure
- infection - esp atypical pneumonia and lung absesses
- head injury
- medications - thiazine diuretics, carbamazapine, SSRI + NSAIDS)
- malignancy - small cell lung carcinoma
- meningitis
SIAD main complication
osmotic demyelination syndrome
- prevention is imperitive as treatment is only supportive
why does diabetes insipidus present with hypernatraemia
because so much water is lost when urinating - due to polydypsia
excess lithium
nephronnic diabetes insipidus
thiazide diuretics suffix
-semide, -thiazide
