Hyponatraemia

Question 1

Early symptoms of hyponatraemia

Answer 1

• Headache
• Nausea
• Vomitting
• General malaise

Question 2

Later signs hyponatraemia

Answer 2

• Confusion
• Agitation
• Drowsiness

May lead to:
* Seizures
* Respiratory depression
* Coma
* Even death

Question 3

Common drug cause of hyponatraemia

Answer 3

• Thiazide diuretics

Question 4

What is important in investigation?

Answer 4

• Drug history
• Fluid status
• Serum and urine osmolarity
• Urine sodium
• Thyroid function
• Cortisol reserve assessment (9am cortisol or synacthen test)

Question 5

Management of acute hyponatraemia with neurological compromise

Answer 5

• Hypertonic saline considered
• To prevent cerebral oedema
• SENIOR decision - under close supervision

Question 6

Diagnostic algorithm for hyponatraemia

Answer 6

• Confirm low serum osmolarity (exclude non-hypo osmolar causes eg hyperglycaemia)
• Once confirmed low check urine osmolarity

Question 7

Urine osmolarity determining treatment for hyponatraemia

Answer 7

• If less than 100mosmol/kg suggests primary polydipsia or inappropriate IV fluids
• If more than 100mosmol/kg urine sodium will guide diagnosis

Question 8

Urine sodium determining hyponatraemia cause

Answer 8

If less than 30mmol/L suggests low effective arterial volume:
* = true dehyration, GI salt loss or overloaded but intravascularly deplete eg CHF, cirrhosis or nephrotic syndrome

If more than 30mmol/L and euvolaemic:
* SIADH
* Exclude ACTH deficiency first

If more than 30mmol/L and dehyrated:
* Addisons
* Renal and cerebral salt wasting
* Vomitting?

Question 9

How can vomitting cause greater than 30mmol/L urine sodium and dehyration? (why not low urine sodium)?

Answer 9

• Vomitting causes loss of hydrogen ions
• = metabolic alkalosis
• corrected by kidney by increased renal excretion of sodium bicarbonate

Question 10

Systemic disease which can cause hyponatraemic not mentioned?

Answer 10

Severe hypothyroidism - unsure how

Question 11

SIADH serum and urine osmolarity and urine sodium

Answer 11

• Low serum osmolarity (less than 275mosmol/kg)
• Urine osmolarity more than 100mosm/kg
• Urine sodium more than 30mmol/L

Question 12

What must we exclude before diagnosing SIADH?

Answer 12

• Hypothyroidism
• Total salt depletion
• ACTH deficiency

Question 13

How does ACTH deficiency present compared to SIADH?

Answer 13

• Identical
• Causes reduced excretion of free water as cortisol deficiency = increased vasopressin activity

Question 14

SIADH causes

Answer 14

• Drugs eg anticonvulsants
• Malignancy - lung cancer
• Respiratory pathology
• CNS pathology

Question 15

What must be done if no cause for SIADH is found?

Answer 15

• Cross sectional imaging or bowel investigation may be needed
• Could be underlying malignancy

Question 16

Management of hypovolaemic hyponatraemia

Answer 16

• 0.9% saline replacement

Question 17

Management of hypervolaemic hyponatraemia

Answer 17

• Specialist treatment of cirrhosis, nephrotic syndrome or CHF

Question 18

SIADH treatment

Answer 18

• Reversal or treatment of cuase
• Fluid restriction 1-1.5L
• Drugs - demeclocycline, ADH antagonists eg Tolvaptan

Question 19

Flow diagram for hyponatraemia causes

Answer 19