Endocrine Abstracts

Introduction: Hyponatraemia is a common biochemical abnormality, complicating up to 15% of all hospital admissions and associated with increased mortality. Hypernatraemia, occuring less frequently, is strongly associated with mortality and is almost always due to a free water deficit. There is limited data about hospital healthcare burden of these two relatively common electrolyte imbalances. We analysed the length of stay, for acute admissions, with reference to the admission sodium value.

Methods: Clinical data for all unscheduled admissions were retrieved from the electronic health record (EHR). We used the CogStack ecosystem to access structured fields in the EHR. We analysed a 12-month cohort of all patients who had an A&E discharge summary created between 1st Jan 2017 and 1st Jan 2018. For each admission, the laboratory U&Es were obtained. Cox proportional hazard model evaluated the independent effect of the first sodium on likelihood of discharge, with first eGFR, age and sex as covariates, both treating sodium as categorical data (hyponatraemia<135 mmol/l and ‘hypernatraemia’ ≥145mmol/l) and continuously using linear spline terms (boundary knots at 135 and 145 mmol/l).

Results: In 12-months, there were 138,307 visits by 98,357 unique patients in the Emergency Department. Laboratory sodium was measured in 36,630 attendances. Hyponatraemia was found on the initial sample in n = 5338 (14.6%), hypernatraemia in n = 360(1%) and eunatraemia in n = 30932 (84.4%). In the multivariable model, hypo- (HR: 0.700, 95% CI 0.678 - 0.722 P = <0.0001) and hypernatraemia (HR 0.572, 95% CI: 0.507 - 0.646 p < 0.0001) were independent predictors of remaining in hospital, after adjusting for eGFR (HR 1.009 (95% CI 1.008 - 1.009; P <0.0001) and age (HR 0.990, 95% CI 0.989-0.990; P = <0.0001). The spline model demonstrated an inverted V shaped relationship between admission Sodium and hazard of discharge against time.

Conclusion: Both low and high sodium are independently associated with prolonged length of stay for acutely hospitalised patients. Further work needs to address if active management of sodium imbalance or salt and water imbalance would achieve earlier discharge.