hypernatraemia W2 Flashcards
central pontine myelinolysis summary?
devastating/fatal condition associated with rapid correction of hyponatraemia (almost always iatrogenic)
related to water fluxes in/out brain
myelin stripped from nerves in pons
commoner in alcoholism, malnutrition, young women
recommended rate of correction of hyponatraemia to avoid CPM?
4-10mmol/l/day if asymptomatic
8-12mmol/l/day if symptomatic
with careful monitoring/observation!!
what is almost always the case with hypernatraemia?
only caused with hypovolaemia
38 yr old lady collapsed, Crohn’s disease with colostomy.
sodium: 152mmol/l
bp: 90/40 lying
why did she collapse?
colonic secretions are water»_space; salt
salt is already absorbed in small bowel
water loss causes hypernatremia
osmotic and hydrostatic forces favour shifts from cells to ECF (but not enough to concentrate sodium back up)
hypernatraemia specific causes?
water loss (fever, hyperventilation, DI)
reduced water intake (iatrogenic, psychological, stroke/coma/confusion)
salt
high sodium intake (iatrogenic)
diabetes insipidus features
ADH insufficient/inactive:
-diuresis continues unabated
-free water loss occurs
-sodium concentrated
-hypernatraemia occurs
-no/failed feedback mechanism
cranial DI caused by what
non/reduced synthesis eg
-pit tumour
-head injury
-meningitis
-genetic
-idiopathic
nephrogenic DI caused by what
reduced tubular response eg
-inherited
-drugs (lithium)
treatment of hypernatraemia?
hydration tends to simply cause polyuria
synthetic ADH (DDAVP) -works in central DI. supranormal doses may work in nephrogenic DI
NSAIDs may help
investigation of hypernatraemia?
history - recent events, new prescriptions?
examination - assessment of volume state, cardiac/resp/neuro disease, examine drug kardex and IV chart
non specific investigations for hypernatraemia (normally routine anyway)
other electrolytes
infection screen
chest X-ray
serum cortisol/synacthen test
CT brain
