The Hyponatraemias Dr JO’Donnell Consultant Clinical Biochemist 22/07/08

Hyponatraemia Working definition Classification How to clinically investigate Treatment

Working Definition Reference range Hyponatraemia in GP practice probably becomes interesting at < 130 and need to do something at <125 (?hospital admission) Is hyponatraemia acute or chronic? Admission criteria – no hard and fast rules but should be considered in all acutes <125 and probably chronics if change in clinical situation

Classification Shock – Hypovolaemic hyponatraemias Dilutional hyponatraemias SIADH and all of that Pseuedo hyponatraemias Endocrine and metabolic causes

Hypovolaemic hyponatraemias Loss of fluid Abdominal catastrophe Burns BUT beware little old lady in nursing home who is not eating and having (insufficient) glasses of water Treatment – admission and fluids

Dilutional Hyponatraemia Water and sodium retention Classic clinical findings - OEDEMA Pathophysiology Treatment - diuretics

SIADH and all that Remember the physiology Rag-bag of conditions Chronic hyponatraemia Aetiology – the trilogy Rarer causes Treatment

Physiology ADH release – both osmolality and hypovolaemia Allows kidneys to retain water

Aetiology Anything in head Anything in chest Drugs Miscellaneous – very rare causes

Treatment of SIADH Treat underlying cause ‘Masterly inactivity’

Pseudohyponatraemias Spurious Analytical – reduced water component of sample Physiological Will rarely occur and we are usually aware

Endocrine and metabolic Hypothyroidism – certainly should be excluded Addison’s Disease (hypoadrenalism) fairly rare but would feel a numptie if missed it Acute porphyria – just to show some of the rare and exotica do present with this

Investigation of hyponatraemia Clinical history (including drugs) – most important Clinical examination (pulse BP and +/- oedema) U and E Serum osmolality TSH and cortisol occasionally. Nothing else really helps!

Some additional bits Renal failure Exogenous fluids Diuretics Bendroflumethiazide In real world, patient will have a bit of heart failure, be on 5-10 drugs any of which can cause SIADH and be a bit hypothyroid – if hyponatraemia not obviously contributing to symptomatology and is stable – probably not a major issue