Case history

Case history #1

A 60-year-old man is admitted to hospital with severe septic shock from pneumonia. He receives vasopressor therapy for hypotension. During the first 10 days of his stay he receives many litres of intravenous fluids, mainly normal saline (0.9%), and has received 10 L in excess of urine volume excretion. On day 5, he develops acute kidney injury with oliguria and his serum sodium concentration is 132 mmol/L. By day 20, his blood pressure and sepsis have improved, as has his renal function. His urine output has progressively increased, urine sodium level is 37 mmol/L, urine potassium level is 42 mmol/L, and urine osmolality is 410 mmol/kg. His serum sodium concentration rises over the next 4 days to 154 mmol/L. At this time, he is no longer receiving intravenous fluids and weighs 8 kg more than when he presented to hospital.

Case history #2

An 85-year-old female nursing home resident with a history of dementia presents to hospital with fever. On admission, her blood pressure is 85/55 mmHg, serum sodium concentration is 174 mmol/L, urine osmolality is 645 mmol/kg, serum urea is 43.8 mmol/L (122 mg/dL), and serum creatinine is 97 micromol/L (1.1 mg/dL).

Other presentations

Patients with diabetes insipidus rarely present with significant hypernatraemia, as their thirst mechanism is sufficient to prevent the development of electrolyte abnormality. However, patients with diabetes insipidus and altered consciousness can develop severe hypernatraemia over a short period of time due to excessive electrolyte-free water excretion. Nephrogenic diabetes insipidus is most commonly seen in the setting of prior lithium therapy. See Diabetes insipidus.

Patients with severe metabolic acidosis who are treated with multiple intravenous boluses of hypertonic sodium bicarbonate can also develop hypernatraemia. These patients are usually hypervolaemic, as are most patients with severe illness who are treated in the intensive care unit. It is preferable, therefore, to give sodium bicarbonate as isotonic infusions rather than in the form of hypertonic intravenous boluses, except in emergencies.[2]

Rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysfunction (ROHHAD) syndrome is a rare, life-threatening condition that is often associated with hypernatraemia.[9]

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