Hyponatremia

Question 1

Define hyponatremia.

Answer 1

A sodium concentration < 135 mEq/liter

Question 2

What are the clinical features of hyponatremia?

Answer 2

1. Asymptomatic
2. Nausea, vomiting, tremors, cramps
3. Altered mental status - coma, seizures
4. Cerebral edema - papilledema
5. Decreased reflexes

Question 3

What is the differential diagnosis for hyponatremia?

Answer 3

Hypotonic Hyponatremia (most common) Hypovolemic, Euvolemic, Hypervolemic

2. Hypertonic hyponatremia
3. Normotonic hyponatremia

Question 4

What are causes of hypotonic hyponatremia?

Answer 4

Excess free water.
If hypovolemic: water/excess sodium losses from GI tract, skin, 3rd spacing, kidneys (diuretics), cerebral salt wasting
If euvolemic: SIADH, hypothyroid, adrenal insufficiency, water intoxication, malnutrition
If hypervolemic - heart failure, liver cirrhosis, nephrotic syndrome

Question 5

What are the causes of hypovolemic hypotonic hyponatremia?

Answer 5

water/excess sodium losses from:
GI tract
skin
3rd space
kidneys via diuretics
cerebral salt wasting

Question 6

What are the causes of euvolemic hypotonic hyponatremia?

Answer 6

SIADH
hypothyroid
adrenal insufficiency
water intoxication
malnutrition

Question 7

What are the causes of hypervolemic hypotonic hyponatremia?

Answer 7

heart failure
liver cirrhosis
nephrotic syndrome

Question 8

What are the causes of hypertonic hyponatremia?

Answer 8

dilutional hyponatremia with a non-sodium solute such as glucose, mannitol, ethanol
TURP syndrome (plasma osmolality variable)

Question 9

What are the causes of normotonic hyponatremia?

Answer 9

TURP syndrome (plasma osmolality variable)

Question 10

What is the management of hyponatremia?

Answer 10

1. Assess duration of hyponatremia and severity
2. Measure osmolality - low normal or high and assess volume status
3. Treat underlying cause
4. Do not correct hyponatremia too quickly! Risk of central pontine myelinolysis
5. Depending on diagnosis, treat with hypertonic saline, isotonic saline, or fluid restriction

Question 11

How would you treat chronic severe hyponatremia?

Answer 11

Slow correction of 0.5 to 1 mEq/L/hr to a maximum of 12 mEq/L/d

Question 12

What can happen if chronic hyponatremia is corrected too quickly?

Answer 12

Central pontine myelinolysis