HYPERNATRAEMIA

Question 1

WHAT IS HYPERNATRAEMIA?

Answer 1

• plasma sodium concentration exceeds 145 mM.

Question 2

WHAT IS THE CAUSE OF HYPERNATRAEMIA?

Answer 2

• usually due to water loss in excess of Na+ loss
  1) fluid loss without water replacement - diarrhoea, vomit, burns
  2) diabetes insipidus - suspect if large urine volume
  3) osmotic diuresis - loop diuretics, diabetes
  4) primary aldosteronism
  5) iatrogenic - incorrect IV fluid replacement (excessive saline)

Question 3

WHAT IS THE MANAGEMENT OF HYPERNATRAEMIA?

Answer 3

• oral water intake if possible, if not give glucose 5% IV slowly
• 0.9% saline IV if hypovalemic

Question 4

WHAT INVESTIGATIONS ARE CARRIED OUT FOR HYERNATRAEMIA?

Answer 4

1) U + E’s with urea, creatinine and glucose- sodium levels high
2) urine osmolality- give indication of cause of hypernatraemia
3) serum osmolality
4) urine electrolytes

Question 5

IF URINE OSMOLALITY > PLASMA OSMOLALITY, WHAT IS THE CAUSE OF HYPERNATRAEMIA, AND IS IT HYPOVALEMIC/ EUVOLAEMIC OR HYPERVOLAEMIC?

Answer 5

• Hypovolaemic hypernatraemia

- GI losses (excessive sweating, diarrhoea), osmotic diuresis, loop diuretics as there is pure volume depletion

Question 6

IF URINE OSMOLALITY < PLASMA OSMOLALITY, WHAT IS THE CAUSE OF HYPERNATRAEMIA AND IS IT HYPOVALEMIC/ EUVOLAEMIC OR HYPERVOLAEMIC?

Answer 6

• Hypervolaemic hypernatraemia (sodium gains)

- primary hyperaldosteronism, sodium cholride tablets, cushing’s syndrome

Question 7

IF URINE OSMOLALITY = PLASMA OSMOLALITY, WHAT IS THE CAUSE OF HYPERNATRAEMIA?

Answer 7

• Euvolaemic hypernatraemia

- renal concentrating defect (inability of kidneys to concentrate urine) such as diabetes insipidus

Question 8

WHAT IS OSMOTIC DIURESIS AND HOW DOES HYPERGLYCAEMIA LEAD TO IT?

Answer 8

• increase of urination rate caused by the presence of certain substances in the small tubes of the kidneys.
• Polydipsia and polyuria occur when blood glucose levels rise high enough to result in excretion of excess glucose via the kidneys, which leads to the presence of glucose in the urine. This produces an osmotic diuresis.

Question 9

WHAT IS THE DANGER OF CORRECTING HYPERNATRAEMIA TO QUICKLY NAD WHY?

Answer 9

• cerebral oedema - fluid build up around the brain
• If hypernatraemia is corrected too quickly in the setting of chronic hypernatraemia, the lowering of the serum osmolality can lead to water movement into the brain cells causing brain oedema.

Question 10

WHAT ARE THE SYMPTOMS OF HYPERNATRAEMIA?

Answer 10

1) thirst
2) irritability
3) seizures
4) hyperreflexia
5) confusion