Disorder of Salt and water balance- CIS

Question 1

Commonly patients who develop hyponatremia typically have an impairment in renal water excretion, most often due to inability to suppress _?

Answer 1

ADH

Question 2

What is pseudohyponatremia and what are some lab findings with pseudohyponatremia?

Answer 2

Pseudohyponatremia is errors in lab measurement of Na. You’ll commonly also see hyperproteinemia, hyperlipidemia, hypercholesterolemia along with hyponatremia.

Question 3

What can hyperglycemia and unmeasured osmol do to your Na level?

Answer 3

Leads to hyponatremia.

Question 4

What are some findings you’d commonly see with true hyponatremia?

Answer 4

1. dilute urine, low ADH

2. Concentrated urine, high ADH

Question 5

What are some diseased conditions where you’d see concentrated urine with high ADH leading to hyponatremia?

Answer 5

1. CHF (decreased effective circulating volume)

2. SIADH

Question 6

What are some conditions where you’d see dilute urine with low ADH leading to hyponatremia?

Answer 6

1. pscyhogenic polydipsia,

2. Pregnancy (reset of osmostat)

Question 7

Why might you see neurological problem with patients with rapid onset of hyponatremia?

Answer 7

Cells can swell due to H20 movement into cells including neural cells in the brain.

Question 8

How do you calculate osmolar gap?

Answer 8

Osmolar gap is the difference between plasma osmolality and measured osmolality. Osmolar gap = (2x Na) + (glu/18) + (BUN/2.8)

Question 9

What is normal level of osmolar gap?

Answer 9

Less then 10

Question 10

What does it mean when a patient has an osmolar gap greater than 10?

Answer 10

It means there’s something else in the plasma that’s adding to the osmolarity that hasn’t been accounted for. For example, pt who ingests antifreeze.

Question 11

What two things needs to be below normal in order for it to be considered true hyponatremia?

Answer 11

Plasma Na concentration and osmolality.

Question 12

How can you tell if a pt was compensating for hyponatremia?

Answer 12

Urine should be dilute and high volume. Pt should have circulating ANP at low levels.

Question 13

What diseased condition can lead to high plasma osmolality and high ADH secretion?

Answer 13

Dehydration, or central DI.

Question 14

In Dehydration what would be the Uosm and Posm ratio? what about in central DI?

Answer 14

Dehydration >1

Central DI

Question 15

If both plasma osmolarity is low and plasma ADH level is low, what clinical condition is likely?

Answer 15

Primary polydipsia.

Question 16

In primary polydipsia what is Usom and Posm ratio?

Question 17

By looking at patient’s hx and chemistry, how can you tell if a patient’s hyponatremia is due to primary polydipsia?

Answer 17

1. Hx of polydipsia
2. Previous diagnosis of Schizo
3. Na, osmolarity measurements (should be low)

Question 18

What condition can cause low osmolarity but high ADH?

Answer 18

SIADH

Question 19

What disease can cause SIADH?

Answer 19

1. Small cell carcinoma.

2. adrenal cortex tumors.

Question 20

How can you differentiate whether a patient’s hypernatremia is nephrogenic or central?

Answer 20

Patients with DI will excrete dilute urine and retain excess salt causing increased osmolarity. You can test to see if the patient is lacking ADH (the brain isnt’ making enough) or if the kidney just isn’t responding to ADH. You would give patients synthetic ADH and see if their urine concentration is increased. If it’s increased then it’s central (the body wans’t making enough), and if it’s not fixed and it’s probably nephrogenic.

Question 21

What is the water deprivation test?

Answer 21

DI patients with hypernatremia and dilute urine, water deprivation test is used to see if ADH is working properly. Patient is derpived of water consumption and an urine sample is taken 6-8 hours later. If urine is dilute compared to baseline then it’s a nephrogenic problem because the kidney isn’t respondign to ADH.

Question 22

In a patient with nephrogenic DI, how would osmolarity change with administration of desmopresin?

Answer 22

Urine osmolarity would not change. Urine desmopresin levels would increase, since the patient isn’t able to use it up.

Question 23

During extrarenal water loss (excessive sweating, fever, diarrhea, vomitting) is urine output decreased or increased? is plasma ADH decreased or increased?

Answer 23

Urine output is decreased. ADH is increased.

Question 24

A patient who is on lithium supplements as a treatment for a psychiatric disorder, presents with hypernatremia? what’s causing this hypernatremia?

Answer 24

Patient’s ADH isn’t working because Li limits the ability of V2 receptors to generate cAMP and decreasess the biologic activity of ADH. the Body is unable to retain water w/o ADH and thus presents with hypernatremia.

Question 25

what electrolyte imbalance is commonly associated with nephrogenic DI?

Answer 25

hypercalcemia and hyperkalemia (associated with acidosis)

Question 26

A patient with Oat cell carcinoma will present with what electrolyte imbalance?

Answer 26

Hyponatremia due to ectopic ADH production (retaining too much water)

Question 27

What are some treatment options for treatment for SIADH?

Answer 27

1. water restriction

2. ADH antagonist like Conivaptin, demeclocycline