Hypernatremia: Epidemiology and Predictive Role in Emerging and Established Acute Kidney Injury.

Hypernatremia (plasma sodium > 145 mmol/L) reflects impaired water balance, and affected patients can suffer from severe neurologic symptoms. Hyponatremia, on the other hand, is the most frequent electrolyte disorder in hospitals. It may be diagnosed in acute kidney injury (AKI), but hyponatremia prior to the diagnosis of AKI has also predictive or prognostic value in the short term. Aim of the article was to summarize data on both, epidemiology and outcomes of in-hospital acquired hypernatremia ("In-hospital acquired" refers to the diagnosis of either hypo- or hypernatremia in patients, who did not exhibit any of these electrolyte imbalances upon admission to the hospital). It also aimed to discuss its predictive role in patients with emerging or established AKI. Five databases were searched for references: PubMed, Medline, Google Scholar, Scopus, and Cochrane Library. Studies published between 2000 and 2023 were screened. The following keywords were used: "hypernatremia", "mortality", "pathophysiology", "acute kidney injury", "AKI", "risk prediction", "kidney replacement therapy", "KRT", "renal replacement therapy", "RRT", "hyponatremia", and "heart failure". A total of 16 studies were deemed eligible for inclusion. Among these, 13 studies had a retrospective design, two investigations were published as secondary analyses from prospective trial cohorts, and one study was prospective in nature. Out of the 16 studies, 11 focused on the epidemiology and outcomes of hypernatremia, while five investigations were related to AKI and/or AKI-associated endpoints. The prevalence of hypernatremia diagnosed during hospitalization varied from 1.9% to 6.8%, with one exception where it was 30.8%. All studies demonstrated associations between hypernatremia and mortality, even over extended periods after discharge. In AKI patients, hypernatremia shows potential for predicting in-hospital death. In conclusion, hypernatremic individuals are at higher risk of death during in-hospital therapy. Also, the electrolyte disorder potentially qualifies as a future biomarker for AKI onset and AKI-associated mortality.