CIS - Mechanisms to Adjust Urine Concentration/Na, Water Balance/Disorders of Osmoregulation Flashcards
hyponatremia
Na to low
fluid movement into cells
hypernatremia
Na to high
fluid movement out of cells
Hypovolemia
not enough ECF volume
ECF volume contraction
Hypervolemia
too much ECF volume
ECF volume expansion
Pseudohyponatermia
hyperproteinemia hyperlipidemia hyperchoelsterolemia hyperlycemia umeasured osmol
True Hyponatremia
Dilute urine, low ADH - reset osmostat (pregnancy) - psychogenic polydipsia Concentrated urine, high ADH - dec ECF volume (CHF, cirrhosis) - SIADH
Uosm/Posm < 1.0
urine osmolarity is low
pt excreting water
high Ch2o
Uosm/Posm > 1.0
urine osmolarity is high
pt holding onto water
low Ch2o
Osmolar Gap
difference between measured plasma osmolality and estimated (calculated) plasma osmolality
important: tells us if an unmeasured solute is present
normal <10mOsm/kg H2O
Ethylene glycol poisoning
increased osmotically activated substance in blood
pulls water from vasculature causing hyponatremia by diluting blood
high osmolar gap
pseudohyponatremia
high serum osmolality
DKA
hyponatremia polydipsia, polyuria glucose in urine high serum osmolality normal osmolar gap
True hyponatremia
plasma Na concentration and osmolality are below normal
Reset osmostat
Pregnancy
- pts are volume expanded causing hyponatremia
Psychogenic Polydipsia
- hx of schizophrenia
- Na and osmolarity both low
- urine specific gravity low
SIADH
pt with lung mass - small cell carcinoma -pulmonary TB ectopic foci for ADH production hyponatremia normal osmolar gap concentrated urine
Tests to distinguish between Nephrogenic and Central DI
- water deprivation test should inc urine osmolarity
- measure ADH
- give Desmopressin and see reaction
Hypernatremia
due to unreplaced water (NOT Na gain)
cell shrink due to hypertonicity
Common causes for Nephrogenic DI
lithium use over long time
Hypercalcemia
Hyperkalemia
Common causes for Central DI
head trauma
postpartum hypophysitis (autoimmune)
hypothalmus or pituitary tumor
Common causes for SIADH
pulmonary TB CHF CNS issue (SVA, sx, trauma) Intubation with mechanical vent Drugs (cyclophosphamide, SSRIs, carbamazepine)
