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 ÂADH
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 ÂNa: diuretics and give free water
o Oral replacement is best if feasible
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