dysnatremic disorders

Question 1

when is ADH released?

Answer 1

when osmolality in the blood is high
when body is volume depleted
if these are in conflict, volume depletion wins.

Question 2

What is required to excrete excess water?

Answer 2

1. No ADH
2. functional DCT
3. enough fluid delivered distally

Question 3

What is required to keep body sufficiently hydrated?

Answer 3

1. increase water intake
2. working countercurrent mechanism
3. ADH
4. tubular response to ADH

Question 4

hyponatremia and relationship with osmolarity

Answer 4

usually hyponatremia is also hypoosmotic
occassionally we see hyponatremia with a hyperosmotic situation:
another factor, like glucose, is in the blood, and this increased osmolarity drives water out of the ICF, thus diluting the Na. treat the diabetes.

Question 5

2 ways to become hyponatremic

Answer 5

1. drink lots of water and don’t pee

2. drink so much water that you overwhelm the kidney’s diluting capacity.

Question 6

hypovolemic hyponatremia causes

Answer 6

vomiting, diarrhea, NG tube loss, thiazide diuretics, burns or sweats accompanied by lots of water intake

Question 7

labs for hypovolemic hyponatremia

Answer 7

conc. of na less than 20 meq/l

BUN: cr over 20:1

Question 8

how do thiazides cause hypovolemic hyponatremia? Why not loops?

Answer 8

thiazides poison the DCT. The DCT is where we normally dilute urine (goes from 200 at end of LOH to 50 at begining of CCT). so, more sodium excretion in comparison to water excretion. But, still, thiazides cause hypovolemia, which induces thirst, which further dilutes the sodium.
Loops don’t do this- they abolish the countercurrent mechanism, so very little water is retained, even in the presence of ADH, because there is not osmotic gradient pushing the water out.

Question 9

hypervolemic hyponatremia

Answer 9

usually because the extra fluid is in the wrong space. caused by CHF, cirrhosis. this causes decreased renal perfusion because the body reacts as though it is volume depleted: increased thirst and ADH release dilutes sodium.

Question 10

euvolemic hyponatremia

Answer 10

many causes, including hypothyroidism, adrenal insufficiency, kidney failure, primary polydipsia, syndrome of inappropriate ADH

Question 11

primary polydypsia

Answer 11

quite rare- must dring 15-20 L in a day. more common among psyche patients. ADH is maximally suppressed and urine diluting ability is retained- the kidney just can’t dilute it enough.

Question 12

syndrome of inappropriate ADH

Answer 12

normal adrenal, renal, and thyroid studies.
non-physiologic ADH secretion.
inappropriately concentrated urine in the setting of hyponatremia
normal sodium handling

Question 13

what is SIADH associated with?

Answer 13

bleeds, CNS surgery, lung pathologies, small cell carcinoma, SSRIs, cyclophosphamides, major surgeries

Question 14

clinical manifestations of hyponatremia

Answer 14

confusion, lethargy, seizure, herniation, death

Question 15

treatment of hyponatremia

Answer 15

return Na to safe level and treat underlying cause. don’t correct sodium faster than 0.5-1 mEq/hr (central pontine myelolysis)

Question 16

treatment for hypovolemic hyopnatremia

Answer 16

IV saline to increase BP and directly increase Na. BP correction will also allow for water excretion

Question 17

hypervolemic hyonatremia treatment

Answer 17

water restriction, loop diurectics to help them loose water. treat underlying cause.

Question 18

SIADH treatment

Answer 18

don’t give salt: they have normal salt excretion and not enough water secretion, so they will actually take saline and excrete it in a more concentrated form than it was given to them, further worsening their problem. do water restriction and loop diuretics. you can also increase sodium intake and give ADH antagonists (DEMECLOCYLINE)

Question 19

hyperosmolality

Answer 19

increase in effective osmolality: shift from the ICF to the ECF. causes are hypernatremia and hyperglycemia

Question 20

causes of hypernatremia

Answer 20

too much salt intake (rare) or not enough water (either not enough in, too much out, or a combo).

Question 21

causes of not enough water in the body

Answer 21

1. not enough water in: rare in alert adults with normal thirst mechanism.
2. too much water out/water loss: sweat, burns, renal, GI.

Question 22

diabetes insipidis

Answer 22

ADH isn’t working. may be central (ADH not secreted: sarcoid, tumor) or nephrogenic (kidney unresponsive to ADH: seen in patients taking LITHIUM. demeclocycline, hypercalcemia, hypokalemia).

Question 23

treatment for hyponatremia

Answer 23

avoid over rapid correction.
give water if there is no sodium loss; give a saline soln if there is sodium loss.
if hypotensive, give isotonic saline before worrying about water deficit.

Question 24

treatment of diabetes insipitis

Answer 24

central: ADH replacement
nephrogenic: vol depletion with low salt diet and thiazide diuretic. this will lead to enhanced proximal NaCl and water absorption. Also, excrete dietary protein