Hyponatremia

Question 1

What is the cause of abnormal [Na+]?

Answer 1

Abnormal [Na+] = Abnormal H20 due to abnormal renal handling +/- intake

Question 2

What conditions are required for maximal free water excretion?

Answer 2

Conditions required for maximal free water excretion:

1. Freely filtered from blood
2. PCT reabsorption
3. “Desalination” (remove salt, leave water)
4. Variable reabsorption (ADH dependent)
5. Excretion with osmoles

Question 3

What are the top 4 causes of SIADH?

Answer 3

1. Malignancy secreting ADH independent of serum sodium concentration or volume
2. Neurological problems ex. inflammatory condition, stroke, hemorrhage
3. Lung conditions
4. Drugs

Question 4

If the serum osmolarity is low (less than 280) then should ADH be on or off?

Answer 4

ADH should be OFF.

Question 5

What are the 3 Cs that can cause SIADH?

Answer 5

Cyclophosphamide - chemotherapy
Carbamazepine - anti-epileptic
Chloropropamide - GI motility drug

Question 6

In the context of hyponatremia an inadequate GFR indicates which mechanism of hyponatremia? Give an example.

Answer 6

If the GFR is inadequate then it is likely due to AKI or CKD.

Question 7

In the context of hyponatremia, a low [Na+] indicates what mechanism of hyponatremia?

Answer 7

If sodium reabsorption is increased in the PCT (resulting in a low urine [Na+]) water reabsorption will increase as well. A low urine [Na+] (especially

Question 8

What are some red flags that the patient’s hyponatremia may be a result of desalination?

Answer 8

If the process of desalination is impaired, then the patient will be unable to dilute the filtrate in the ascending LoH; the urine osmolality is close to the serum osmolality. This may be due to the use of diuretics or an inherited tubular disorder ex. Loop diuretics, thiazide diuretics, Bartter’s, Gitelman’s. Clues may include hypokalemia and metabolic acidosis on labs.

Question 9

What are the mechanisms of hyponatremia if the urine osmolality is >100 and

Answer 9

1. What is the urine osmolality? If the urine osmolality is >100 then it could be that the patient is experiencing anti-diuresis. This can be caused by a reduced EABV and SIADH.
2. If the urine osmolality is