Pathophysiology of Water Handling Flashcards
Osmoregulation is achieved by ____________.
water excretion and intake
What two things can stimulate the release of ADH?
The baroreceptors of the aortic arch and carortid sinus
Osmoreceptors
ADH increases exponentially if the blood volume decreases by _________, even despite decreases in osmolarity.
6% - 8%
Severe volume depletion can cause ___________.
hyponatremia, because volume depletion induces ADH release and subsequent water resorption
Hypo- and hypernatremia refer to states of ______________.
sodium concentration, not total sodium content
Hypertonic hyponatremia is most often caused by ____________.
uncontrolled diabetes
Isotonic hyponatremia can result from _____________.
lab artifact, hyperlipidemia, or hyperproteinemia
Other than hemorrhage, what can cause hypovolemic hyponatremia?
GI losses
Renal loss (excessive diuretic use or mineralocorticoid deficiency)
Excessive sweating
How is hypovolemic hyponatremia treated?
Give normal saline to restore blood volume
Why is ADH released in those with liver cirrhosis?
The splanchnic vasculature is excessively dilated, which is sensed by the body as decreased effective blood volume. This stimulates ADH release.
How is hypervolemic hyponatremia treated?
Water and salt restriction Loop diuretics (stop thiazides) Inotropes for CHF
What usually causes euvolemic hyponatremia?
Excessive ADH release
SIADH is characterized by ____________.
euvolemic hyponatremia and urine that is not maximally dilute (that is, greater than 50 to 100 mOsm/kg)
What causes SIADH?
Carcinomas (duodenum, pancreas, and small cell carcinoma)
CNS disorders
Pulmonary diseases
How can euvolemic hyponatremia be treated?
Hypertonic saline for seizures
Water restriction
Removal of causative drugs
ADH antagonists
If hyponatremia is chronic (or its duration isn’t known), slow correction to avoid ____________.
central pontine myelinolysis
List some causes of hypovolemic hypernatremia and hypervolemic hypernatremia.
Hypovolemic hypernatremia: renal or extrarenal water losses in excess of sodium losses
Hypervolemic hypernatremia: addition of hypertonic fluids (usually iatrogenic)
What are causes of central diabetes insipidus?
Idiopathic
Hypotalamus or pituitary gland disorders (head trauma, surgery, tumors, encephalitis)
Acquired nephrogenic DI disorders are ________ common than congenital ones.
more
What is DDAVP?
A synthetic form of vasopressin
What is the formula for serum osmolarity?
Osm = 2 x [Na] + [BUN]/2.8 + [glucose]/18
What releases ADH?
The posterior pituitary
What most often causes hypertonic hyponatremia?
Uncontrolled diabetes
What is the first clinical thing you should do after discovering that someone has “true” hyponatremia (i.e., hypotonic hyponatremia)?
Check their volume status using the history, BP, HR, lung sounds, and presence/absence of edema
What three things can cause hypervolemic hyponatremia?
CHF (deacreased tissue perfusion induces the kidneys to retain lots of water and some additional sodium), liver cirrhosis (discussed in another card), and renal failure leading to decreased excretion of fluids and sodium
Water leaves through passive diffusion in the _______________. Sodium leaves through active transport in the ___________.
descending loop of Henle; thick ascending loop of Henle
Free water excretion capacity is roughly _________ of GFR.
20% (so if your GFR is 120 liters per day, then you could–in theory–excrete a maximum of 24 liters in one day)
Maximal urine dilution is _____________.
50 mOsm/kg
What can cause excessive ADH release?
Hypothyroidism Adrenal insufficiency Nausea Pain Psychosis Medications (commonly SSRIs, NSAIDs, and anti-psychotics)
Hypernatremia typically develops when ___________.
people can’t drink water or have CNS impairments that limit thirst
What can cause acquired diabetes insipitus?
Chronic hypercalcemia or hypokalemia Lithium treatment Obstruction Sickle cell Chronic kidney disease
What causes gestational diabetes insipitus?
Release of vasopressinase from the placenta
What is the treatment for hypernatremia?
D5W
What is the formula for rehydration?
water needed = 0.6 x (body weight) x ([actual Na]/[desired sodium] -1)
The response of ADH to ________ is less sensitive than the response to increases in serum osmolarity.
volume depletion
Hyponatremia is the inability of the body to _____________.
maximally dilute the urine coupled with continuous water intake
