Prevent hypernatraemia by adequate fluid therapy in patients with fluid loss.
In hypernatraemia, the plasma sodium concentration is above 148 mmol/l.
Avoid too rapid resolution of chronic (lasting > 48 hours) hypernatraemia.
Ensure that fluid intake (at least 1.5-2 l/day) is monitored in elderly patients with inadequate thirst control, especially if they have fever and during hot weather.
Reference values
Plasma sodium 137-145 mmol/l
Symptoms and signs of hypernatraemia
Related to blood volume deficit: thirst, dry mucous membranes, dysphagia, decreased skin elasticity, hypotension
From the central nervous system: confusion, somnolence, neck stiffness, convulsions, loss of consciousness
Causes of hypernatraemia
Water deficit (hypovolaemic hypernatraemia)
Insufficient fluid intake (the elderly and demented patients)
Absent sensation of thirst (hypothalamic damage)
Intensive evaporation through the skin and mucous membranes (fever, burn injuries)
Deficient production or action of antidiuretic hormone (ADH), e.g. in association with lithium use
Water and salt deficit, dominated by water deficit (hypovolaemic hypernatraemia)
In a patient with hypernatraemia, examine urine osmolality.
Urine osmolality <250 mosm/kg H2O in a hypernatraemic patient is a sign of deficient production or action of ADH. Consult an endocrinologist as necessary.
Determine daily fluid intake and diuresis as well as plasma copeptin concentration. Copeptin forms a part of the precursor of ADH and is secreted in equimolar amounts with ADH (cf. C peptide and insulin). In ADH deficiency the concentration of copeptin is low, and in deficient action of ADH (renal diabetes insipidus) it is high.
Central ADH deficiency and renal ADH resistance may also be differentiated by administering 2 µg of desmopressin i.v. or i.m. If the disorder is central the hourly amount of urine is decreased and urine becomes more concentrated (urine osmolality increases > 50%) in the next few hours.
Treatment
Water deficit can be roughly estimated on the basis of the patient's plasma sodium concentration and body weight. Sodium concentration of 160 mmol/l in a patient weighing 60 kg corresponds to a water deficit of 4.5 litres, and in a patient weighing 80 kg the deficit is 6.0 litres, respectively.
5% glucose or hypotonic (0.45%) fluid is administered perorally or intravenously, for example 200 ml/h. If blood pressure is low, start with balanced electrolyte solution (e.g. Ringer's).
If hypernatraemia is caused by ADH deficiency, treatment with desmopressin is started: first, if deemed necessary, a 1-2 µg single dose intravenously, and thereafter either 1-2 µg twice daily subcutaneously or 60-120 µg 3 times daily orally.
In hypervolaemic hypernatraemia, the kidneys remove excess water and salt; in renal failure, furosemide can be tried.
In acute (lasting ≤ 48 hours) hypernatraemia, the aim is to decrease plasma sodium rapidly, within 24 hours, to the reference range; requires treatment in intensive care or on a monitoring ward. Dialysis treatment is an alternative.
Excessively rapid fluid administration may lead to brain oedema and worsen the neurological symptoms in chronic hypernatraemia. The aim for sodium concentration correction rate is 10 mmol/l/24 h, the maximum being 12 mmol/l/24 h.