Hyponatreamia

Causes

• Most common cause is diuretics
• If urinary Na $>$ 20 mmol/L - Addison's, renal failure (early stage), diuretic excess, osmolar diuresis (raised glucose, urea)
• If urinary sodium $<$ 20 mmol/L - Diarrhoea, vomiting, fistula, burns, small bowel obstruction
• If patient is oedematous -- nephrotic syndrome, cardiac failure, liver cirrhosis, renal failure
• If urine osmolality is $>$ 500 mmol/kg - inappropriate ADH

Investigations

• U&E, urinary spot sodium, plasma and urinary osmolality

Management

• Aim for gradual increase in plasma Na
• If dehydrated - and kidney function good, give 0.9% saline.
• If not dehydrated - and Na $<$ 125 mmol/L, restrict water to 0.5 to 1 litre/day if tolerated. Consider Frusemide 40-80 millegrammes/24 hour