Disorders of Water Balance Flashcards
a hypertonic environment has what effect on ADH levels
- increases ADH levels
what does ADH release cause
- increased tubular reabsorption of water
after the body fluid has been diluted and is now isotonic, what happens to ADH release and thirst reflex
- inhibition of ADH release
- inhibition of thirst
maximally dilute urine has what osmolality
- 50-100
maximally dilute urine occurs under what conditions
- large water intake
- no ADH
maximally concentrated urine has what osmolality
- 1200
maximally concentrated urine under what condition
- low water intake
- high ADH levels
osmoreceptors respond to what signal
- high plasma osmolality
sensitivity of osmoreceptors
- highly sensitive
- respond to 1-2% change
low pressure baroreceptors respond to what signal
- decreased extracellular fluid volume
sensitivity of low pressure baroreceptors
- lowly sensitive
- respond to 5% change
high pressure baroreceptors respond to what signal
- decreased blood pressure
sensitivity of high pressure baroreceptors
- low sensitive
- respond to 5% change
direct neural receptors respond to what signals
- drugs
- vomiting
- stress
- ADH
between osmoreceptors, low pressure and high pressure baroreceptors, and direct neural receptors, which are physiologic responses
- osmoreceptors
- low pressure and high pressure baroreceptors
between pressure/volume and osmolality, which will cause greater release of ADH
- pressure/volume trumps osmolality
ICF is estimated by calculating
- effective osmolality
ICF is proportional to
- 1/effective osmolality
sodium concentration is equal to
- H2O balance
ECF is estimated by
- physical examination
what parts of the physical exam would lead you to think increased ECF
- edema
- crackles
- elevated JVP
what parts of the physical exam would lead you to think decreased ECF
- low BP
- increased pulse
- decreased capillary refill
- no edema
ECF volume =
Na+ balance
exceptions when total body sodium would not correlate with the clinical assessment of ECF volume
- SIADH
- pure water loss
what happens in SIADH
- increased ECF
- decreased total body Na
reabsorbing lots of free water and increasing ECF volume
clinical shorthand for serum electrolytes
Na I Cl I BUN /
I I / Glucose
K I HCO3 I Creat \
definition of hyponatremia
- sodium concentration < 135 mEq/L
how to calculate sodium concentration
ECF Na+ content
ECF H2O content
If you have hypotonic hyponatremia and the urine Osm < 100 and the urine Na levels are < 20, what is the problem?
why would you have urine Osm < 100 and the urine Na levels are < 20
- primary polydipsia - drinking too much water
- low solute intake - not eating enough salt
- ADH is not absorbing any additional water or concentrate the urine
If you have hypotonic hyponatremia and the urine Osm > 100 and you are hypovolemic, what is your urine sodium concentration
- less than 20
If you have hypotonic hyponatremia and the urine Osm > 100 and you are hypovolemic and your urine Na concentration is less than 20, what is the cause
- true hypovolemia
- vomiting, diarrhea, burns
you are losing lots of water so your RAAS system is activated. You are reabsorbed sodium through aldosterone so your urine concentration of Na is low.
If you have hypotonic hyponatremia and the urine Osm > 100 and you are hypervolemic, what is your urine sodium concentration
less than 20
If you have hypotonic hyponatremia and the urine Osm > 100 and you are hypervolemic and your urine Na concentration is less than 20, what is the cause
- CHF
- Cirrhosis
- Nephrosis
your RAAS system is activated due to decreased perfusion to the heart and so you have aldosterone reabsorbed Na but you are hypervolemic because of edema and leakage elsewhere
If you have hypotonic hyponatremia and the urine Osm > 100 and you are euvolemic, what is your sodium concentration in your urine
> 40
If you have hypotonic hyponatremia and the urine Osm > 100 and you are euvolemic and your urine Na concentration is greater than 40 what is the cause
- SIADH
your ADH is overproduced and you are reabsorbing lots of water but not solutes. with euvolemia, RAAS is not activated so you won’t reabsorb Na.
some causes of SIADH
- vigorous exercise
- tumors
- NSAIDS
- SSRIs
- Ecstacy
diagnosis of pseudohyponatremia
- normal serum sodium
- increased osmolal gap
- asymptomatic
- normal ECF volume
- increased lipoproteins or protein
when might you have increased lipoproteins or proteins
- myeloma
how to calculate osmolal gap
- measured Osm - calculated Osm
normal osmolal gap
< 10 mOsm/Kg
causes of hypertonic hyponatremia
- hyperglycemia
- mannitol
- glycine
- sorbitol
- sucrose
when does acute hyponatremia occur (time frame)
- 1-2 days
when does chronic hyponatremia occur (time frame)
- after 3 days
how do we treat symptomatic hyponatremia
- 3% saline
treatment of hypotonic hyponatremia when patient is hypovolemic
- give fluids
- isotonic saline
treatment of hypotonic hyponatremia when patient is euvolemic
- fluid restriction
- salt tablets
- loop diuretics
- V2 antagonist
- 3% saline
- demeclocycline
treatment of hypotonic hyponatremia when patient is hypervolemia
- Na+ fluid restriction
- diuretics
safe goal for rapid correction of hyponatremia
- 4-6 mEq/L in 24 hours
side effects of rapid correction of hyponatremia
- osmotic demyelination syndrome
- OR central pontine myelinolysis
- axonal demyelination
- rapid increase in sodium
hypernatremia definition
- concentration of Na > 145 mEq/L
what is diabetes insipidus
- ADH not working
what is primary polydispia
- just drinking a lot of water
if you are doing a water deprivation test and you have a high urine osmolarity, what is the most likely cause
- patient is just drinking too much water
if you are doing a water deprivation test and you have a low urine osmolality, what is the most likely cause
what do you do next
- something isn’t absorbing the water and concentrating urine
- do a desmopressin test
if you are doing a water deprivation test and you have a low urine osmolality and patient responds to desmopressin by increasing concentration of urine, what is the cause
- central diabetes insipidus
- gestational diabetes insipidus
if you are doing a water deprivation test and you have a low urine osmolality and patient does not respond to desmopressin and urine concentration remains low what is the cause
- nephrogenic diabetes insipidus
what is diuresis
- excessive production of urine
what is a negative effect of rapid treatment of hypernatremia
- cerebral edema
