Persistent hyponatraemia as a predictor of in-hospital mortality in acute pulmonary embolism

Abstract Introduction Hyponatraemia on admission is a recognised predictor of mortality in acute pulmonary embolism (PE) and is thought to reflect neurohormonal activation secondary to right ventricular dysfunction and low cardiac output. However, the prognostic relevance of sodium dynamics during hospitalisation remains underexplored. Purpose To assess whether correction of hyponatraemia during hospitalisation mitigates the risk of in-hospital mortality (IHM) and whether persistent hyponatraemia identifies a higher-risk phenotype. Methods Retrospective single-centre study of 178 patients admitted for acute PE in a Cardiology Department. Hyponatraemia was defined as plasma sodium ≤135 mmol/L. The population was stratified into three groups based on sodium dynamics between admission and discharge (or death): (1) Normonatraemia (sodium >135 mmol/L on admission and discharge); (2) Corrected Hyponatraemia (admission sodium ≤135 mmol/L normalised to >135 mmol/L); (3) Persistent Hyponatraemia (admission sodium ≤135 mmol/L remaining ≤135 mmol/L). The primary endpoint was IHM. Fisher’s exact test was used for subgroup comparisons. Results Mean age was 63±18 years and 61.2% were women. Hyponatraemia on admission was present in 11.2% (n=20). Of these, 15 patients (75%) corrected their sodium levels during hospitalisation, while 5 patients (25%) maintained persistent hyponatraemia. Global IHM was 5.6%. Subgroup analysis revealed a marked prognostic gradient. Patients with corrected hyponatraemia had an IHM of 6.7% (1/15), similar to the normonatraemia group (3.4%, 5/147; p=0.447). By contrast, patients with persistent hyponatraemia had an IHM of 60.0% (3/5), significantly higher than both the corrected group (p=0.032) and the normonatraemic group (p<0.001). Conclusion Sodium dynamics during hospitalisation provide prognostic information beyond the admission value alone. While patients who correct hyponatraemia have a favourable prognosis comparable to normonatraemic patients, persistence of hyponatraemia is associated with a very high in-hospital mortality rate in this cohort. Failure to correct sodium levels identifies a readily recognisable high-risk phenotype in acute PE and warrants further confirmation in larger studies.In-hospital mortality by sodium dynamicsFor image description, please refer to the figure legend and surrounding text.