Hyper and hyponatraemia Flashcards
Define hyponatraemia
Categories the different types of hyponatraemia
Na+ <135 mmol/L
- Hyponatraemia with:
- Hypovolaemia
- Euvolaemia
- Hypervolaemia
Give three causes of hyponatraemia with hypovolaemia
Extra-renal losses: Urinary Na+ <20 mmol/L
- DaV; haemorrhage; burns; sweating
Renal losses: Urinary Na+ >20 mmol/L
- Osmotic diuresis eg. hyperglycaemia; diuretics
- Addison’s disease
- Tubulo-interstitial renal disease
- Unilateral renal artery stenosis
- Recovery phase of ATN
How does hyponatraemia with hypovolaemia present?
Dominated by features of volume depletion
- Fatigue
- Reduced skin turgor
- Sunken eyes
- Prolonged (>2s) CRT
- Weakness
- Tachycardia
- Hypotension
Give two causes of hyponatraemia with euvolaemia
- Abnormal ADH release
- SIADH: eg. antipsychotics; antidepressants
- Hypothyroidism
- Increased ADH sensitivity
- ADH-like subtances; oxytocin
- Chronic alcohol abuse
List three causes of hyponatraemia with hypervolaemia
- Secondary hyperaldosteronism
- HF; cirrhosis
- Nephrotic syndrome
- IV dextrose
- Psychogenic polydipsia
What is SIADH?
Syndrom of inappropriate ADH secretion
Dilutional hyponatraemia secondary to excessive water retention
Provide four causes of SIADH
- Small cell lung cancer
- Stroke; SAH; meningitis
- TB; pneumonia
- SSRIs; TCAs; carbamazepine; sulfonyureas
List four presenting features of hyponatraemia
Often asymptomatic if mild/moderate or chronic
Mild (130-134mmol/L)/moderate (120-129 mmol/L):
- Headache; dizzinesss
- Lethargy
- NaV
- Muscle cramps
- Confusion
Severe (<120 mmol/L): Seizures; coma; brainstem herniation
Sudden fall to 125 mmol/L can result in convulsions
Request three investigations for suspected hyponatraemia
- U+Es: Addison’s disease
- LFTs
- Osmolality (paired serum and urine)
- Serum hypo-osmolality to confirm SIADH
- Urinary Na+ and K+
- TFTs
- Cortisol
- CXR; CT head
Outline the management of hyponatraemia
Acute symptomatic hyponatraemia is medical emergency: Hypertonic sodium chloride 3%
Chronic/asymptomatic:
- Correct underlying cause
- Sodium chloride (not hypertonic)
- Fluid restriction if SIADH
What is the commonest cause of acute hyponatraemia in adults?
Post-operative iatrogenic hyponatraemia
Typically severe, therefore a medical emergency
What complication can occur with hyponatraemia?
Rapid hyponatramia: Severe cerebral oedema and herniation
What complication can occur if hyponatraemia is over-corrected?
How does this present?
Central pontine myelinolysis (Osmotic demyelination syndrome)
Two days after over-correction of severe hyponatraemia:
- Quadriplegia
- Pseudobulbar palsy
- Locked-in syndrome
What is the limit for sodium correction daily in hyponatraemia?
4-6 mmol/L/d
Over-correction risks osmotic demyelination syndrome
Name three causes of hypernatraemia
- Dehydration
- Diabetes insipidus
- Excessive IV sodium chloride
