Objective: To study the frequency, outcome and association with neurological signs and symptoms of severe hyponatraemia (< 120 mmol/l) in adult hospitalised patients.
Design: Retrospective study of severe hyponatraemia using laboratory data to identify patients.
Setting: 800 bed peri-urban hospital in the former homeland of Transkei.
Subjects: All adult inpatients from the medical and surgical wards with severe hyponatraemia during a 10 month period of which 18 cases records could not be traced and one was antefactual.
Main outcome measures: Incidence of severe hyponatraemia, mortality, admission hyponatraemia, hospital acquired hyponatraemia, neurological symptoms and outcome.
Results: The overall incidence of severe hyponatraemia was 1.1%. Among the 58 patients (mean age 49.3 years), pulmonary tuberculosis (24%), Diabetes mellitus (19%) and renal failure (17.2%) were the principal aetiological conditions occurring in approximately 60% of hyponatraemic patients. A high mortality rate of 44.8% was observed which was probably associated with the severity of the underlying disease. 36.2% of patients had serum sodium levels of less than 115 mmol/l with a significantly (p < 0.05) higher mortality (62%) than those with values greater than 115 mmol/l (32%). Admission hyponatraemia (63.8%) was more frequent (p < 0.05) than hospital acquired hyponatraemia (36.2%); in the latter, hyponatraemia was more likely to normalise (p < 0.05). Neurological signs and symptoms developed in 17.2%, this being associated with a high mortality and lower mean serum sodium levels of 112 mmol/l respectively. Following therapy, serum sodium levels normalised in nearly half the patients. In three (5.2%) patients, the hyponatraemia worsened whilst another three became hypernatraemic.
Conclusion: The incidence of severe hyponatraemia was lower than that observed in developed countries. It was associated with severe underlying disease and had a high mortality rate. Patients whose hyponatraemia did not normalise were more likely to have higher mortality.