Hypernatremia

Question 1

Hypernatremia is not a problem of too much sodium, it’s a problem if too little water
True or false

Answer 1

True

Question 2

What are some conditions which could cause free water losses in excess of sodium loss

Answer 2

Febrile illness
Burns
Diarrhea
Diuretics

Question 3

What are the two causes of hypernatremia

Answer 3

Lack of access to free water
Free water loss in excess of sodium loss

Question 4

What are some special causes of hypernatremia

Answer 4

Diabetes insipidus (loss of ADH effects) - polyruria and polydipsia (also seen in diabetes mellitus)

Question 5

How does diabetes insipidus manifest in babies and adults

Answer 5

Babies: frequent wet diapers
Adults: frequent thirst, nocturia

Question 6

What are some causes of nephrogenic diabetes insipidus

Answer 6

Hyoercalcemia
Hypokalemia (severe < 3 mEq/L)
Drugs (lithium, amphotericin B)

Question 7

In particular you can sometimes see hypernatremia in patients who have central diabetes insipidus. Why

Answer 7

Central lesion in central DI can impair thirst which means you don’t have access to free water

Question 8

How do you diagnose diabetes insipidus

Answer 8

Best first test: water deprivation (after 8 hours of no fluid, urine sample should be concentrated. If urine is dilute - urine osmolality between 50 to 200 range, patient has absent or ineffective ADH effects
Next step: administer desmopressin (activates renal V2 ADH receptors and by doing this urine should be concentrated provided kidneys are working and are able to respond to ADH. If there’s no urine concentration, patient has a nephrogenic DI, if desmopressin works and urine becomes concentrated, patient has central DI

Question 9

In a water deprivation test, if patient has a concentrated urine, what condition is he or she likely to have

Answer 9

Psychogenic polydipsia

Question 10

What is the treatment for hyponatremia

Answer 10

Water
IV fluids (D5W)

Question 11

You need to be cautious when treating hypernatremia. Treating it too quickly (over-rapidly correcting hypernatremia) may result in

Answer 11

Cerebral edema

Question 12

What is the maximum correction for hypernatremia to prevent cerebral edema

Answer 12

Don’t correct above 12mEq/L/day

Question 13

How is central diabetes insipidus treated

Answer 13

Desmopressin (has no vasopressor effects - does not raise the blood pressure by causing vasoconstriction in contrast to vasopressin)

Question 14

Why can’t nephrogenic diabetes insipidus be treated with desmopressin

Answer 14

For patients with nephrogenic diabetes insipidus, the problem in them is not that there isn’t enough ADH around, it’s that the kidneys can’t respond to ADH

Question 15

How is nephrogenic diabetes insipidus treated

Answer 15

Treat hypercalcemia or hypokalemia
Thiazide diuretics (causes water to be reabsorbed in the PCT because it cannot be reabsorbed in the collecting ducts in patients with nephrogenic DI - paradoxical antidiuretic effect)
NSAIDs (inhibit renal synthesis of prostaglandins - ADH antagonists)