Hypo + Hypernatraemia Flashcards
(28 cards)
What is hypernatremia?
High plasma Na+ conc
>146mmol/L
Causes of hypernatremia
- osmotic diuresis e.g. uncontrolled diabetes
- fluid loss without replacement e.g. sweating, burns, vomiting
- diabetes insipidus
- incorrect IV fluid replacement
- primary aldosteronism
Symptoms of hypernatraemia
- thirst
- apathy
- irritability
- weakness
- confusion
- reduced consciousness
- seizures
- hyperreflexia + spasticity
- coma
What is apathy?
a lack of motivation or lack of interest in things around you
Different types of hypernatremia + their causes
Hypovolaemic hypernatraemia
- osmotic diuresis
- loop diuretics
- intrinsic renal disease
- excessive sweating
- burns
- diarrhoea
.
- Euvolaemic hypernatraemia:
- diabetes insipidus
- hypodipsia
.
Hypervolaemic hypernatraemia:
- primary hyperaldosteronism
- Cushing’s syndrome
- hypertonic dialysis
- sodium chloride tablets
Treatment of hypernatraemia
- identify underlying cause + reverse if possible
- increase water intake
- IV fluids dextrose in water - no sodium
- monitor sodium levels
Symptoms of hyponatraemia
- headache
- N+V
- malaise
- confusion
- agitation
- drowsiness
- gait imbalance
Investigations of hyponatraemia
- plasma osmolality
- urine osmolality
- urine Na+
- TFTs
- cortisol levels
- CT head if suspected SIADH
- drug history
- hydration status
Diagnostic pathway of hyponatarmia
- exclude non-hypo-osmolar hyponatraemia (e.g. hyperglycaemia)
- is the patient hypovolaemic?
- if yes, check urinary Na+:
- if >20mmol/L: renal Na+ loss - Addison’s, renal failure, diuretics, osmotic diuresis
- if <20mmol/L: loss elsewhere - diarrhoea, vomiting, burns, SBO, excessive sweating
- if no (hypervolaemic): nephrotic syndrome, cardiac failure, cirrhosis, renal failure
- if euvolaemic, check urine osmolality:
- if >300mOsm/kg - SIADH
- if <300mOsm/kg, water intoxication, severe hypothyroidism, glucocorticoid insufficiency
Causes of hypovolaemic hyponatraemia
Check urinary Na+
- if >20mmol/L: renal loss - Addison’s, renal failure, diuretics, osmotic diuresis
- if <20mmol/L: loss elsewhere - diarrhoea, vomiting, burns, SOB, excessive sweating
Causes of hypervolaemic hyponatraemia
Nephrotic syndrome
Cardiac failure
Cirrhosis
Renal failure
Causes of euvolaemic hyponatremia?
Check urine osmolality
- if >300mOsm/kg - SIADH
- if <300mOsm/kg - water intoxication, severe hypothyroidism, glucocorticoid insufficiency
Why does vomiting cause hyponatramia?
causes loss of H+ > metabolic alkalosis
corrected by renal excretion of sodium bicarbonate
What drugs can cause hyponatremia?
- thiazides
- SSRIs
- PPIs
- ACEi
- loop diuretics
Treatment of hypovolaemic hyponatraemia
- give IV fluids: 0.9% saline at 1-3ml/kg/hour
- give K+ if needed
Diagnosis of SIADH
after exlusion of hypothyroidism, total salt depletion + ACTH deficiency
What is SIADH characterised by?
low serum osmolality
urine osmolaility >100mosol/kg
urine Na >30mmol/l
treatment of SIADH
- fluid restriction <800ml/day
- PO sodium chloride
- furosemide
- demeclocycline induces diabetes insipidus (opposite to SIADH)
Treatment of hypervolaemic hyponatraemia
fluid restrict to 500-1000ml a day
consider furosemide + vaptans
What is the risk of correcting hyponatraemia too fast?
- too rapid correction of chronic hyponatraemia leads to central pontine myelinosis
- aim to correct <12mmol/L/day
Treatment of acute hyponatraemia
3% hypertonic saline IV bolus +/- furosemide
Treatment of chronic hyponatraemia
- hypertonic saline bolus if seizures present
- isotonic saline + furosemide if not
- aim to correct 8mmol/L in 24 hours
- fluid restriction if asymptomatic
- stop offending drugs
How do you calculate osmolarity?
Osmolarity = (2xNa) + glucose + urea
mmol/L
What is cerebral salt wasting syndrome?
Renal loss of Na+ during intracranial disease
- Causes hyponatremia + decrease in extracellular fluid volume
