Hypernatraemia

Hypernatraemia

·        Indicates ICF volume contraction

·        Usually not due to ­ total body sodium – total sodium is low, normal or high. Kidney is good at excreting excess Na (except if swamped – eg near drowning)

·        Always means the patient is hyperosmolar

·        Thirst and ­ADH protect against hyperosmolality Þ don‟t see hypernatraemia where the thirst mechanism is normal and there is access to water

·        Cellular dehydration ® neurologic symptoms: lethargy, weakness, irritability, seizures, etc. Cerebral oedema if it is rapidly corrected

·        Classification:

o   Water and sodium deficiency with water loss > sodium loss (ie lost hypotonic fluid), eg vomit, diarrhoea, sweat, osmotic diuresis (urine osmolarity not low), burns

o   With normal total body sodium (pure water depletion): unable to drink (old, babies, sick, etc), central or nephrogenic diabetes insipidous 

o   With increased total body sodium: excess iv hypertonic saline, ingestion of sea water, mineralocorticoid excess (low sodium output) (Þ expanded ECF)

·        Treatment:

o   Chronic: may be asymptomatic even at 170 – 180 mmol/l due to adaptation by brain Þ gradual correction

o   If water deficit then:

§  Stop the water loss: give ADH, prevent osmotic diuresis, etc

§  SLOWLY give oral water or iv dextrose (Watch for hyperglycaemia, rate ~ 300 ml/hr. Add sodium if history suggests loss of sodium containing fluid and patient is not polyuric)

§  Aim for Na reduction of 1 mmol/L/hr and no more than 12 mmol/24 hours

o   If ­Na: diuretics and give free water

o   Oral replacement is best if feasible