HYPONATRAEMIA

Hyponatraemia < 120mmol/L

Metabolic encephalopathy
(water into brain cells + cerebral edema)

- confusion
- seizure
- coma

Rapid correction-- central pontine myelinosis
Do not increase sodium concentration by > 0.5mmol/L
cautious admin of isotonic 0.9% sodium chloride + use of loop diuretics (frusemide)

Hypertonic saline is dangerous.

Sodium deficit

140-measured Na+ x 0.2 x height(kg)

why 0.2? 20% ECF- sodium is the main cation

If ECF normal or increased-- IV water admin and sodium decreased

Will correct spontaneously if water intake is decreased
ALthough less common in surgical patient  SIADH promotes tubular reabsorption of water
Independently of sodium concentration---- inappropriately concentrated urine

(>100mOsm/L) in face of hypotonic plasma (>290mOsm/L)

Therefore urine osmolality helps to distinguish SIADH from excess IV admin. Spot measurement of urine sodium will be high

In patients with decreased ECF volume.
Hyponatraemia combined water and sodium deficiency

Diarrhoea
Diuresis
Adrenal insufficiency

Tx: 0.9% NaCl