Hyponatraemia Flashcards
Early symptoms of hyponatraemia
- Headache
- Nausea
- Vomitting
- General malaise
Later signs hyponatraemia
- Confusion
- Agitation
- Drowsiness
May lead to:
* Seizures
* Respiratory depression
* Coma
* Even death
Common drug cause of hyponatraemia
- Thiazide diuretics
What is important in investigation?
- Drug history
- Fluid status
- Serum and urine osmolarity
- Urine sodium
- Thyroid function
- Cortisol reserve assessment (9am cortisol or synacthen test)
Management of acute hyponatraemia with neurological compromise
- Hypertonic saline considered
- To prevent cerebral oedema
- SENIOR decision - under close supervision
Diagnostic algorithm for hyponatraemia
- Confirm low serum osmolarity (exclude non-hypo osmolar causes eg hyperglycaemia)
- Once confirmed low check urine osmolarity
Urine osmolarity determining treatment for hyponatraemia
- If less than 100mosmol/kg suggests primary polydipsia or inappropriate IV fluids
- If more than 100mosmol/kg urine sodium will guide diagnosis
Urine sodium determining hyponatraemia cause
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?
How can vomitting cause greater than 30mmol/L urine sodium and dehyration? (why not low urine sodium)?
- Vomitting causes loss of hydrogen ions
- = metabolic alkalosis
- corrected by kidney by increased renal excretion of sodium bicarbonate
Systemic disease which can cause hyponatraemic not mentioned?
Severe hypothyroidism - unsure how
SIADH serum and urine osmolarity and urine sodium
- Low serum osmolarity (less than 275mosmol/kg)
- Urine osmolarity more than 100mosm/kg
- Urine sodium more than 30mmol/L
What must we exclude before diagnosing SIADH?
- Hypothyroidism
- Total salt depletion
- ACTH deficiency
How does ACTH deficiency present compared to SIADH?
- Identical
- Causes reduced excretion of free water as cortisol deficiency = increased vasopressin activity
SIADH causes
- Drugs eg anticonvulsants
- Malignancy - lung cancer
- Respiratory pathology
- CNS pathology
What must be done if no cause for SIADH is found?
- Cross sectional imaging or bowel investigation may be needed
- Could be underlying malignancy