Hypernatraemia and Hyponatraemia

Question 1

What is the normal range of serum sodium?

Answer 1

135-145mmol/L

Question 2

What is considered life-threatening hypernatraemia?

Answer 2

> 160mmol/L

Question 3

What metabolic issue could cause these signs and symptoms?

Lethargy, thirst, weakness, irritability, confusion, coma, signs of dehydration.

Answer 3

Hypernatraemia

Question 4

What are the causes of hypernatraemia?

Answer 4

Usually due to water loss in excess of Na+ ions (dehydration):

1. Fluid loss w/o water replacement (diarrhoea, vomiting, burns)
2. Diabetes insipidus if large urine volumes (may follow head/CNS injury)
3. Osmotic diuresis (DKA)
4. Primary hyperaldosteronism, rarely severe
5. Iatrogenic (excessive saline)

Question 5

What is the management for hypernatraemia?

Answer 5

1. Water orally if possible

2. If not, glucose 5% IV, 1L over 6h

Question 6

What can the over-rapid correction of hypernatraemia lead to?

Answer 6

Cerebral oedema

Question 7

What is considered life-threatening hyponatraemia?

Answer 7

<115

Question 8

What metabolic issue could cause these signs and symptoms?

Anorexia, nausea, malaise, headache, irritability, confusion, low GCS, seizures.

Answer 8

Hyponatraemia

Question 9

What are the causes of hyponatraemia?

Answer 9

1. Hypovolaemic - dehydration, diarrhoea, vomiting, diuretics, ACEi, nephropathies, Addison’s.
2. Euvolaemic - SIADH, post-operative, hypothyroidism, beer potomania, ACTH deficiency.
3. Hypervolaemic - CHF, liver disease, nephrotic syndrome, advanced renal failure.

Question 10

What is the management for hypovolaemic hyponatraemia?

Answer 10

IV saline, stop diuretics.

Question 11

What is the management for euvolaemic hyponatraemia?

Answer 11

Restrict fluid to 1L/d, stop diuretics, thyroxine if hypothyroid and steroids if deficient.

Question 12

What is the management for hypervolaemic hyponatraemia?

Answer 12

Restrict fluid to 1L/d, restrict sodium.

Question 13

What can the over-rapid correction of hyponatraemia lead to?

Answer 13

Central pontine myelinolysis (pons demyelinates)

Question 14

What is the criteria for diagnosing SIADH?

Answer 14

1. Concentrated urine (urine Na >20)
2. Hyponatraemia (plasma Na <125)
3. Low plasma osmolality (<260)
4. Absence of hypovolaemia, oedema, or diuretics.
5. Clinical and biochemical improvement with fluid restriction.