hyponatraemia Flashcards
what are the early and late symptoms and signs of hyponatraemia?
early symptoms
- headache
- nausea
- vomiting
- general malaise
late symptoms
- confusion
- agitation
- drowsiness
- seizures
- respiratory depression
- coma
- death
acute severe hyponatraemia requires urgent treatment under senior supervision
what investigation is done into hyponatraemia?
- full history and examination
- thiazide diuretics are a common cause
- check serum osmolality, urine osmolality, urine sodium, thyroid function and asses cortisol reserve (0900 cortisol or synacthen test)
when can hypertonic be saline be considered in acute severe hyponatraemia?
when there is acute severe hyponatraemia with neurological compromise
a senior decision that should be done under close supervision
in mild/moderate cases, the diagnostic algorithm should be followed
what is the diagnostic algorithm for hyponatraemia?
confirm low serum osmolality to exclude non hypo osmolar hyponatraemia e.g hyperglycaemia
once hypotonic hyponatraemia is confirmed, urine osmolality should be checked
urine osmolality <100 suggests primary polydipsia or inappropriate IV fluid administration
if urine osmolality >100 urine Na will guide differentials
what does a urine sodium <30 mmol/L suggest?
low effective arterial volume
seen in true dehydration e.g GI salt loss or where patients are overloaded but have intra vascular depletion e.g Congestive cardiac failure, cirrhosis or nephrotic syndrome
what does a urine sodium >30 mmol/L suggest if the patient is euvolaemic?
SIADH should be considered
exclude ACTH deficiency
what does a urine sodium of >30 mmol/L suggest if the patient is dehydrated?
need to rule out
- addisons
- renal and cerebral salt wasting
- history of vomiting
- severe hypothyroidism
what is SIADH ?
syndrome of inappropriate ADH
characterised by
- low serum osmolality
- high urine osmolality
- urine Na >30 (high)
when can SIADH be diagnosed?
need to exclude
- hypothyroidism
- total salt depletion
- ACTH deficiency
NB: ACTH deficiency can appear similar to SIADH as it causes reduced excretion of free water, since cortisol deficiency leads to increased vasopressin activity
what can cause SIADH?
- malignancy, commonly lung cancer
- Respiratory and CNS pathology
- drugs e.g anticonvulsants
what is the management for hyponatraemia?
cause specific
appropriate fluid replacement in hypervolaemic hyponatraemia with normal saline
reverseal/treatment of SIADH cause and fluid resusitation is key for treatment
strict fluid restriction (1-1.5L) is poorly tolerated and hard to achieve
drug treatment for SIADH includes demeclocycline and ADH antagonists
what are the possible causes low Urine Na <30 mol/L in hyponatraemia?
Low effective arterial volume
- heart failure
- portal hypertension
- nephrotic syndrome
- hypoalbuminaemia
- third space loss
- GI loss
- previous diuretic use
what are the the causes of high urine Na >30 mmol/L in hyponatreamia ?
normal apparent circulating volume
- SIADH
- AVP like drugs
- NSAID
low apparent arterial volume
- primary salt wasting
- vomiting
- hypoadrenalism
