An underlying cause should be sought in all patients with hyponatraemia. Assessment of volume status and, in some patients, serum and urine osmolality and osmolar gap can help direct initial treatment.
- Acute hyponatraemia is a medical emergency that can cause permanent brain damage, coma and death.
- Chronic hyponatraemia is common and can cause forgetfulness, ataxia, asterixis and drowsiness but is usually asymptomatic.
- History and examination can help determine the patient’s volume status and guide initial treatment.
- In all cases, an underlying cause should be sought and if possible corrected.
- Water-overloaded (hypervolaemic) and euvolaemic patients need fluid restriction, and dry (hypovolaemic) patients need intravenous saline to correct hyponatraemia.
- Measurement of serum and urine osmolality and calculation of the osmolar gap can clarify some cases.
- In most patients, hyponatraemia is multifactorial and resolves after assessment of volume status, medication review and treatment of the underlying condition.