HYPONATRAEMIA

Question 1

WHAT IS HYPONATRAEMIA?

Answer 1

• serum sodium concentration of <135 mmol/L.
• disorder of water balance reflected by an excess of total body water relative to electrolytes (total body sodium and potassium) leading to low plasma osmolality.

Question 2

WHAT ARE THE EARLY SYMPTOMS OF HYPONATRAEMIA?

Answer 2

1) headache
2) nausea
3) vomiting
4) general malaise

Question 3

WHAT ARE THE LATER SIGNS OF HYPONATRAEMIA?

Answer 3

1) confusion
2) agitation
3) drowsiness

Question 4

WHAT ARE THE CONSEQENCES OF ACUTE SEVERE HYPONATRAEMIA?

Answer 4

1) seizures
2) respiratory depression
3) coma
4) death

Question 5

WHAT INVESTIGATIONS WOULD YOU CARRY OUT FOR HYPONATRAEMIA?

Answer 5

1) Drug history - thiazide diuretics (prevent sodium reabsorption, increasing fluid loss in urine)
2) Hydration status
3) Serum sodium concentration
4) Serum osmolality - differentiate if it is hypotonic or hypertonic hyponatraemia
5) Urine sodium concentration
6) Urine osmolality - high (SIADH), normal, low (primary polydipsia)
7) Thyroid function test
8) Synacthen

Question 6

WHAT IS THE MANAGEMENT FOR ACUTE SEVERE HYPONATRAEMIA AND WHY?

Answer 6

3% hypertonic saline IV boluses to prevent cerebral oedema

Question 7

WHAT DOES CEREBRAL OEDEMA OCCURS IN HYPONATRAEMIA?

Answer 7

Resulting decrease in plasma osmolality causes water movement into the brain in response to the osmotic gradient, thus causing fluid accumulation and raised ICP

Question 8

WHAT DOES A HIGH URINE OSMOLALITY INDICATE?

Answer 8

• SIADH

Question 9

WHAT DOES A LOW URINE OSMOLALITY INDICATE?

Answer 9

• primary polydipsia

- inappropriate administration of IV fluids (fluid overload)

Question 10

WHAT IS HYPOTONIC HYPONATRAEMIA?

Answer 10

hyponatremia associated with a low plasma osmolality

Question 11

WHAT IS HYPERTONIC HYPONATRAEMIA?

Answer 11

low sodium levels but there is no hypotonicity.

Question 12

IN HYPOVALEMIC HYPONATRAEMIA WHAT DOES A URINE SODIUM > 30 mmol/l INDICATE?

Answer 12

renal sodium loss i.e. diuretics

Question 13

IN HYPOVALEMIC HYPONATRAEMIA WHAT DOES URINE SODIUM < 30 mmol/l INDICATE?

Answer 13

non renal sodium loss therefore GI salt loss, true dehydration

Question 14

IN HYPERVALEMIC HYPONATRAEMIA WHAT DOES A URINE SODIUM >30 mmol/l INDICATE?

Answer 14

AKI/ CKI

Question 15

IN HYPERVALEMIC HYPONATRAEMIA WHAT DOES A URINE SODIUM < 30 mmol/l INDICATE?

Answer 15

congestive heart failure, cirrhosis - fluid overload

Question 16

WHAT ARE THE 3 BIOCHEMICAL CHARACTERISTICS OF SIADH?

Answer 16

• low serum osmolality
• high urine osmolality
• high urine sodium concentration

Question 17

WHAT DO YOU NEED TO EXCLUDE PRIOR TO SIADH DIAGNOSIS?

Answer 17

• hypothyroidism
• total salt depletion - vomiting, diarrhoea
• ACTH deficiency (appears identical to SIADH)

Question 18

WHAT IS THE MANAGEMENT OF HYPOVALEMIC HYPONATRAEMIA?

Answer 18

• normal saline

Question 19

WHAT IS THE MANAGEMENT OF HYPERVALEMIC HYPONATRAEMIA?

Answer 19

• fluid restriction and consider furosemide