Hypernatraemia is due to a failure in urine concentration by the kidneys. This results in the loss of hypotonic urine with a result that there is a rise in total body sodium which is reflected by hypernatraemia. Clinical evidence of dehydration may be evident in haemodynamic variables eg pulse, arterial blood pressure and jugular (central) venous pressure, and also a fall in urine output.
Most patients with hypernatraemia secondary to water loss may not appear dehydrated as water loss without sodium does not lead to overt volume contraction; and the increased osmolality may be compensated by increased drinking (see polyuria)
Insensible losses are likely with febrile illnesses and hypermetabolic states associated with poor fluid intake.
- Kumar S, Berl T. Sodium. Lancet 1998;352:220-228.