Characteristics, management and outcomes of patients with hyponatraemia presenting to an Irish tertiary hospital.

Objective: Hyponatraemia is the most common electrolyte abnormality in clinical practice and is associated with increased in-hospital mortality and length of stay (LOS). The aims of this study were to evaluate the prevalence of hyponatraemia in adult medical inpatients, compliance with consensus guidelines regarding evaluation and management of hyponatraemia, LOS and mortality. Design: This was a retrospective single-centre observational study conducted in a tertiary-level Irish hospital. Methods: Adult patients admitted under the medical services over a 2-month period with a serum sodium (sNa) <135 mmol/L were included. Patients were classified according to nadir sNa during their admission; mild, moderate and severe hyponatraemia were defined as an sNa between 130 and 134 mmol/L, 125-129 mmol/L and <125 mmol/L respectively. Clinical information was gathered retrospectively. Results: 486 patient episodes of hyponatraemia were included. The prevalence of hyponatraemia was 32.9%. The median age was 78 (min-max: 16-100) years and 239 (49.0%) were female. The median nadir sNa was 132 (min-max: 105-143) mmol/L. Eighty-seven (17.9%) and 48 (9.9%) patients had moderate and severe hyponatraemia. In cases of moderate and severe hyponatraemia, the most common cause of hyponatraemia was hypovolaemia (n = 33, 24.4%). Ninety-one patients (67.4%) with moderate and severe hyponatraemia had active treatment of hyponatraemia and 33 (24.4%) had input from a specialist service. The mean LOS was 15.0 (±22.5), 19.3 (±21.7) and 21.2 (±45.5) (P = 0.01) days in mild, moderate and severe hyponatraemia, respectively. Overall inpatient mortality was 7.0% (n = 34). Conclusions: Hyponatraemia is often incompletely investigated and suboptimally managed, with insufficient input from specialist services sought in a large tertiary hospital. Hyponatraemia therefore represents a potential intervention target to reduce inpatient morbidity, mortality and healthcare costs. Significance statement: Hyponatraemia is a common electrolyte disturbance among hospitalised patients, associated with increased morbidity, mortality and healthcare costs. In this retrospective study of medical inpatients at an Irish tertiary hospital, we found a high prevalence (32.9%) of hyponatraemia, with significant gaps in its investigation, diagnosis and management. Hypovolaemic hyponatraemia was the most frequent aetiology in moderate-to-severe cases, yet diagnostic tools and volume assessments were often underutilised. Suboptimal treatment approaches, including low rates of fluid restriction for SIADH, were evident. Our findings highlight the need for improved education, protocolised care and early specialist involvement to enhance outcomes. These results are generalisable to other centres, emphasising hyponatraemia as a key target for improving inpatient care and reducing healthcare costs.