Hyponatraemia Flashcards

1
Q

Early symptoms of hyponatraemia

A
  • Headache
  • Nausea
  • Vomitting
  • General malaise
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2
Q

Later signs hyponatraemia

A
  • Confusion
  • Agitation
  • Drowsiness

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

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3
Q

Common drug cause of hyponatraemia

A
  • Thiazide diuretics
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4
Q

What is important in investigation?

A
  • Drug history
  • Fluid status
  • Serum and urine osmolarity
  • Urine sodium
  • Thyroid function
  • Cortisol reserve assessment (9am cortisol or synacthen test)
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5
Q

Management of acute hyponatraemia with neurological compromise

A
  • Hypertonic saline considered
  • To prevent cerebral oedema
  • SENIOR decision - under close supervision
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6
Q

Diagnostic algorithm for hyponatraemia

A
  • Confirm low serum osmolarity (exclude non-hypo osmolar causes eg hyperglycaemia)
  • Once confirmed low check urine osmolarity
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7
Q

Urine osmolarity determining treatment for hyponatraemia

A
  • If less than 100mosmol/kg suggests primary polydipsia or inappropriate IV fluids
  • If more than 100mosmol/kg urine sodium will guide diagnosis
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8
Q

Urine sodium determining hyponatraemia cause

A

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?

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9
Q

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

A
  • Vomitting causes loss of hydrogen ions
  • = metabolic alkalosis
  • corrected by kidney by increased renal excretion of sodium bicarbonate
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10
Q

Systemic disease which can cause hyponatraemic not mentioned?

A

Severe hypothyroidism - unsure how

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11
Q

SIADH serum and urine osmolarity and urine sodium

A
  • Low serum osmolarity (less than 275mosmol/kg)
  • Urine osmolarity more than 100mosm/kg
  • Urine sodium more than 30mmol/L
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12
Q

What must we exclude before diagnosing SIADH?

A
  • Hypothyroidism
  • Total salt depletion
  • ACTH deficiency
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13
Q

How does ACTH deficiency present compared to SIADH?

A
  • Identical
  • Causes reduced excretion of free water as cortisol deficiency = increased vasopressin activity
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14
Q

SIADH causes

A
  • Drugs eg anticonvulsants
  • Malignancy - lung cancer
  • Respiratory pathology
  • CNS pathology
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15
Q

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

A
  • Cross sectional imaging or bowel investigation may be needed
  • Could be underlying malignancy
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16
Q

Management of hypovolaemic hyponatraemia

A
  • 0.9% saline replacement
17
Q

Management of hypervolaemic hyponatraemia

A
  • Specialist treatment of cirrhosis, nephrotic syndrome or CHF
18
Q

SIADH treatment

A
  • Reversal or treatment of cuase
  • Fluid restriction 1-1.5L
  • Drugs - demeclocycline, ADH antagonists eg Tolvaptan
19
Q

Flow diagram for hyponatraemia causes

A
20
Q
A