Water Balance Flashcards
water balance is maintained by?
osmotic release or inhibition of ADH, kidney response to ADH, stimulation of thirst
at a tonicity of below 275, ADH is turned ____ and urine osmolarity will be _____
off; less than 100 (maximally dilute)
why does our body let us become hypotonic?
non-osmotic release of ADH in setting of decreased blood pressure, ECF volume, or drugs, vomiting, stress, SIADH
is ADH more sensitive to osmolality or pressure/volume changes?
osmolality
intracellular fluid volume is based on ____ of sodium, while extracellular fluid volume is based on ____ of sodium
concentration; total amount
when do you see hypotonic hyponatremia?
diarrhea, sweating (initially there is hypernatremia, but thirst and non-osmotic release of ADH results in hyponatremia)
treatment of SIADH
water restriction, NS (or hypertonic in emergency)
common causes of SIADH
tumors, CNS, lung dz, drugs, post-op, endurance exercise, PPV
what is the only example of hyponatremia in setting of shrunken cells?
diabetes
when do you get osmotic demyelination syndrome?
correct hyponatremia too quickly
who can get pseudohyponatremia?
pts with severe hyperlipidemia or multiple myeloma (light chains and lipids are mistaken as water)
how common is hypernatremia?
10-25% of ICU pts, 40% of them die!
hypernatremia is due to?
pure water loss or loss of hypotonic sodium
causes of pure water loss hypernatremia
impaired mentation, stroke, hypothalamic lesion, functional impairment, diabetes insipidus (rare: can be central or resistant)
causes of hypotonic sodium loss (leading to hypernatremia)
upper GI losses (vomiting, NG suctioning)
causes of hypotonic sodium and potassium loss (leading to hypernatremia)
diuretics, osmotic diuresis, diarrhea
causes of hypertonic sodium gain (leading to hypernatremia)
administration or ingestion of NaCl or NaClO3 without proportional amounts of water (water leaves the cells)
causes of polyuria with dilute urine
water diuresis
cause of polyuria with concentrated urine
osmotic diuresis (solute such as glucose in lumen)
what should you do to evaluate a patient with water diuresis?
deprive them of water and see what happens: if urine remains dilute then they have diabetes insipidus, if it concentrates then they have primary polydipsia
how do you distinguish between nephrogenic and central diabetes insipidus?
give desmopressin; urine will concentrate if it is central, will remain dilute if nephrogenic
what is the only type of hypernatremia that results in increased ECF volume?
hypertonic sodium gain
