Background: Although hyponatraemia [plasma sodium (PNa)<136 mmol/l] frequently develops in hospital, risk factors for hospital-acquired hyponatraemia remain unclear.
Methods: Patients who presented with severe hyponatraemia (PNa<or=125 mmol/l) were compared with patients with hospital-acquired severe hyponatraemia in a 3 month hospital-wide cohort study.
Results: Thirty-eight patients had severe hyponatraemia on admission (PNa 121+/-4 mmol/l), whereas 36 patients had hospital-acquired severe hyponatraemia (PNa 133+/-5-->122+/-4 mmol/l). In hospital-acquired hyponatraemia, treatment started significantly later (1.0+/-2.6 vs 9.8+/-10.6 days, P<0.001) and the duration of hospitalization was longer (18.2+/-11.5 vs 30.7+/-23.4 days, P=0.01). The correction of PNa in hospital-acquired hyponatraemia was slower after both 24 h (6+/-4 vs 4+/-4 mmol/l, P=0.009) and 48 h (10+/-6 mmol/l vs 6+/-5 mmol/l, P=0.001) of treatment. Nineteen patients (26%) from both groups were not treated for hyponatraemia and this was associated with a higher mortality rate (seven out of 19 vs seven out of 55, P=0.04). Factors that contributed to hospital-acquired hyponatraemia included: thiazide diuretics (none out of 38 vs eight out of 36, P=0.002), drugs stimulating antidiuretic hormone (two out of 38 vs eight out of 36, P=0.04), surgery (none out of 38 vs 10 out of 36, P<0.001) and hypotonic intravenous fluids (one out of 38 vs eight out of 36, P=0.01). Symptomatic hyponatraemia was present in 27 patients (36%), and 14 patients died (19%).
Conclusions: The development of severe hyponatraemia in hospitalized patients was associated with treatment-related factors and inadequate management. Early recognition of risk factors and expedited therapy may make hospital-acquired severe hyponatraemia more preventable.