Pathophysiology of Water Handling

Question 1

Osmoregulation is achieved by ____________.

Answer 1

water excretion and intake

Question 2

What two things can stimulate the release of ADH?

Answer 2

The baroreceptors of the aortic arch and carortid sinus

Osmoreceptors

Question 3

ADH increases exponentially if the blood volume decreases by _________, even despite decreases in osmolarity.

Answer 3

6% - 8%

Question 4

Severe volume depletion can cause ___________.

Answer 4

hyponatremia, because volume depletion induces ADH release and subsequent water resorption

Question 5

Hypo- and hypernatremia refer to states of ______________.

Answer 5

sodium concentration, not total sodium content

Question 6

Hypertonic hyponatremia is most often caused by ____________.

Answer 6

uncontrolled diabetes

Question 7

Isotonic hyponatremia can result from _____________.

Answer 7

lab artifact, hyperlipidemia, or hyperproteinemia

Question 8

Other than hemorrhage, what can cause hypovolemic hyponatremia?

Answer 8

GI losses
Renal loss (excessive diuretic use or mineralocorticoid deficiency)
Excessive sweating

Question 9

How is hypovolemic hyponatremia treated?

Answer 9

Give normal saline to restore blood volume

Question 10

Why is ADH released in those with liver cirrhosis?

Answer 10

The splanchnic vasculature is excessively dilated, which is sensed by the body as decreased effective blood volume. This stimulates ADH release.

Question 11

How is hypervolemic hyponatremia treated?

Answer 11

Water and salt restriction
Loop diuretics (stop thiazides) 
Inotropes for CHF

Question 12

What usually causes euvolemic hyponatremia?

Answer 12

Excessive ADH release

Question 13

SIADH is characterized by ____________.

Answer 13

euvolemic hyponatremia and urine that is not maximally dilute (that is, greater than 50 to 100 mOsm/kg)

Question 14

What causes SIADH?

Answer 14

Carcinomas (duodenum, pancreas, and small cell carcinoma)
CNS disorders
Pulmonary diseases

Question 15

How can euvolemic hyponatremia be treated?

Answer 15

Hypertonic saline for seizures
Water restriction
Removal of causative drugs
ADH antagonists

Question 16

If hyponatremia is chronic (or its duration isn’t known), slow correction to avoid ____________.

Answer 16

central pontine myelinolysis

Question 17

List some causes of hypovolemic hypernatremia and hypervolemic hypernatremia.

Answer 17

Hypovolemic hypernatremia: renal or extrarenal water losses in excess of sodium losses
Hypervolemic hypernatremia: addition of hypertonic fluids (usually iatrogenic)

Question 18

What are causes of central diabetes insipidus?

Answer 18

Idiopathic

Hypotalamus or pituitary gland disorders (head trauma, surgery, tumors, encephalitis)

Question 19

Acquired nephrogenic DI disorders are ________ common than congenital ones.

Answer 19

more

Question 20

What is DDAVP?

Answer 20

A synthetic form of vasopressin

Question 21

What is the formula for serum osmolarity?

Answer 21

Osm = 2 x [Na] + [BUN]/2.8 + [glucose]/18

Question 22

What releases ADH?

Answer 22

The posterior pituitary

Question 23

What most often causes hypertonic hyponatremia?

Answer 23

Uncontrolled diabetes

Question 24

What is the first clinical thing you should do after discovering that someone has “true” hyponatremia (i.e., hypotonic hyponatremia)?

Answer 24

Check their volume status using the history, BP, HR, lung sounds, and presence/absence of edema

Question 25

What three things can cause hypervolemic hyponatremia?

Answer 25

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

Question 26

Water leaves through passive diffusion in the _______________. Sodium leaves through active transport in the ___________.

Answer 26

descending loop of Henle; thick ascending loop of Henle

Question 27

Free water excretion capacity is roughly _________ of GFR.

Answer 27

20% (so if your GFR is 120 liters per day, then you could–in theory–excrete a maximum of 24 liters in one day)

Question 28

Maximal urine dilution is _____________.

Answer 28

50 mOsm/kg

Question 29

What can cause excessive ADH release?

Answer 29

Hypothyroidism
Adrenal insufficiency
Nausea
Pain
Psychosis 
Medications (commonly SSRIs, NSAIDs, and anti-psychotics)

Question 30

Hypernatremia typically develops when ___________.

Answer 30

people can’t drink water or have CNS impairments that limit thirst

Question 31

What can cause acquired diabetes insipitus?

Answer 31

Chronic hypercalcemia or hypokalemia
Lithium treatment
Obstruction
Sickle cell
Chronic kidney disease

Question 32

What causes gestational diabetes insipitus?

Answer 32

Release of vasopressinase from the placenta

Question 33

What is the treatment for hypernatremia?

Answer 33

D5W

Question 34

What is the formula for rehydration?

Answer 34

water needed = 0.6 x (body weight) x ([actual Na]/[desired sodium] -1)

Question 35

The response of ADH to ________ is less sensitive than the response to increases in serum osmolarity.

Answer 35

volume depletion

Question 36

Hyponatremia is the inability of the body to _____________.

Answer 36

maximally dilute the urine coupled with continuous water intake