Overview
Hypernatraemia is a serum sodium concentration >145mmol/L. This may be caused by losing water, gaining salt or by redistribution of water within the body.
Pathogenesis
Causes of Hypernatraemia
Water Loss
- Inadequate water intake
- Diabetes insipidus (neurogenic / nephrogenic)
- Loop diuretics
- Acute tubular necrosis (polyuric phase)
- Osmotic diuresis (e.g. poorly controlled diabetes)
- Non-urinary loss - insensible, sweat, burns, diarrhoea
Salt Gain
- Excessive administration - dietary excess, hypertonic saline, hypertonic dialysis
- Endocrine - hyperaldosteronism, Cushings
Water Redistribution
- Strenuous exercise
- Seizure
Manifestations
Clinical Features
- Thirst
- Lethargy
- Weakness
- Confusion
- Seizures
- Coma
Diagnosis
Interpretation
Assess the urinary osmolality and sodium.- Low urine osmolality (<800mOsm/kg) - due to renal water lossDiabetes insipidus, loop diuretics, ATN, uncontrolled diabetes
- High urine osmolality (>800mOsm/kg) - due to other causesInsensible loss, sweat, GI loss, excessive administration
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