Severe hyponatraemia: investigation and management in a district general hospital

To study the incidence, investigation, and management of severe hyponatraemia (serum sodium < 120 mmol/litre) over a period of six months in a district general hospital.

The laboratory computer was used to identify all inpatients who had a serum sodium concentration of less than 120 mmol/litre over a six month period. The records of these patients were reviewed for the relevant demographic, clinical, and laboratory data, in addition to diagnosis, treatment, and outcome of hospitalisation.

Forty two patients were studied, with a female to male ratio of 2 : 1. Nine patients had central nervous system symptoms, and four of these patients died in hospital. Only 14 patients had their urinary electrolytes and/or osmolality checked. A diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was mentioned in eight patients, sometimes without checking their urinary electrolytes or osmolality. Twenty one patients died in hospital. The patients who died did not have lower serum sodium values or a higher rate of correction of hyponatraemia, but they all suffered from advanced medical conditions.

The possible cause of hyponatraemia should always be sought and that will require an accurate drug history, clinical examination, and assessment of fluid volume, plus the measurement of urinary electrolytes and osmolality in a spot urine sample. The diagnosis of SIADH should not be confirmed without the essential criteria being satisfied. The current or recent use of diuretics is a possible pitfall in the diagnosis of SIADH. The rate of serum sodium correction of less than 10 mmol/day is probably the safest option in most cases.