Jan8 M1-Disorders of Water Balance Flashcards
cause and consequence of water imbalance ultimately
ADH is cause. Hypo and hyperNa is consequence
what controls plasma Na conc
water balance
consequence of too much Na and too little Na (not related to water balance)
too much = edema
not enough = volume depletion
main worry in Na imbalances
neuron swelling in the brain (cerebral edema)
what can cause cerebral edema (swelling of neurons)
HYPOTONIC hyponatremia
cause of central pontine myelinolysis
too rapid correction of hypoNa or hyperNa
4 types of water excretion impairment hyponatremias and volume state in each
- circulating volume depletion (low IV volume. can have high ECF volume though bc high ISF volume)
- SIADH (euvolemic)
- advanced renal failure (hypervolemia)
- hormonal changes (euvolemia)
conditions where appropriate ADH release with high ECF volume but low IV volume and ones with low ECF
CHF, cirrhosis, nephrotic syndrome
diarrhea, vomiting: high ECF low IV volumes
low ECF: diarrhea, vomiting, volume depletion with thiazides
causes of SIADH and mechanisms
- neuropsychiatric disorder (any CNS disorder) or severe pain or nausea (signaling to hypothalamus)
- lung tumor (making ADH)
- pulmonary diseases (unknown)
- drugs
volume state, Na and osms in SIADH
euvolemic, hypoosmolar, hypoNa
hormonal changes that can cause water excretion impairment hypoNa and mechansims
- hypothyroidism (thyroid contributes to water excretion)
- cortisol deficiency (adrenal problem and low BP, perceived as low volume)
- pregnancy
4 questions in hypoNa history
- why hospitalized?
- concurrent illnesses (renal disease, thyroid, low cortisol=Addison’s)
- medications (diuretics**)
- pain and nausea
how to assess volume status in general
intravascular: BP, HR, urine output, JVP, postural hypotension BP
extravascular: edema and where
what’s a postural hypotension BP
check BP diff when seat after lying down and if >10, hypovolemia
how to approach hypoNa and determine the cause
depending on volumee status
hypoNa causes in hypovolemia
water loss (dehydration, diarrhea, vomiting), meds like diuretics
hypoNa causes in euvolemia
SIADH, thyroid, adrenal insufficiency
hypoNa causes in hypervolemia
CHF, liver disease, nephrotic syndrome, advanced renal failure
most common causes of severe hypoNa
- SIADH,
- thiazide diuretics
- postoperative state (pain and nausea)
- GI fluid loss
- polydipsia in psychiatric patients (rare)
formula for plasma osmolality
2 x Na + glucose + urea + (alcohol)
4 criteria to diagnose SIADH
U Na>40
U osms>100
Na<125
serum osms<275
why do you not retain volume or develop edema in SIADH (and stay euvolemic)
when sense excess volume, aldo and AT2 turned off so Na excreted
hypoNa that is not a water excretion impairment
reset osmostat (hypothalamus is reset to be thirsty at a lower osmolality during pregnancy)
ADH turned on or off in reset osmostat
turned off
fluid treatment in hypoNa with peripheral edema + ADH before and after
fluid restrict to limit water reabso and return Na back up
ADH turned on initially and still turned on after
fluid treatment in hypovolemia due to GI loss + ADH before and after
isotonic saline. ADH on before and turned off after
fluid treatment in SIADH + ADH before and after
hypertonic saline (ADH on before and after, it’s constitutively active..)
D5W composition + what are we giving
water with 300 mosms of dextrose (is like giving pure water)
normal saline composition
0.9% (0.9g per 100 mL NaCl): 154 mEq Na and 154 mEq Cl
half NS composition and used when
77 mmol of Na. maintenance when not drinking or eating before surgery
d5w + 3 ampules of NaHCO3 composition + used when
145 meq or Na and 145 meq of HCO3 per L (used in acid base disorder when need bicarb)
3% saline composition and used when
513 mmol Na per L. SIADH
Adrogue formula for Na correction
change = (infusate Na - serum Na)/(TBW + 1)
long term treatment in SIADH
water restriction, dietary Na, loop diuretic to wipe out medullary interstitium osmotic gradient
goal for speed of Na correction
5 mM per 12 hours
why NS doesn’t work in SIADH hypoNa
patient is euvolemic so extra Na seen is secreted
2 categories of causes of hyperNa
- increased water losses unreplaced due to impairment of thirst
- administration of hypertonic NaCl or NaHCO3
hyperNa due to increased water losses unreplaced due to impairment of thirst: 4 types
- insensible and sweat losses (fever, resp infections) (hypotonic)
- urinary losses (central or nephrogenic DI: ADH not working, or osmotic diuresis with glucose or mannitol)
- GI loss (hypotonic)
- lesion to hypothalamic thirst center
hyperNa is usually caused by what 2 things
fluid deficit (volume contraction) and inability/failure to drink
first formula to estimate water deficit
TBW x (Na/140 - 1) = water deficit in L
2nd formula to estimate water deficit
C1V1 = C2V2
V1 and V2 being TBW
treatment to hyperNa
give water (d5w)
why NS doesn’t work for hyperNa
NS outplaced by the ongoing hypotonic losses of water (sweat, GI, etc.)
would have to give too much saline to retrieve normal Na
ADH turned on or off in hypernatremia
on (osmotic receptors in the hypothalamus)
