Sodium and Water Homeostasis in Children: Pathogenesis, Diagnosis, and Treatment

Maintaining homeostasis in the body through water and sodium management is essential, and the central nervous system and kidneys play a key role in this process. However, knowledge of the diagnosis and treatment of these conditions in pediatric patients is still unsystematized. There are no up-to-date guidelines on managing children with sodium imbalance. Since sodium shifts are inextricably linked to water changes in the body, they should always be pondered together. Each of the sodium disorders should be considered in the context of changes in the vascular volume, whether it is hypo-, eu-, or hypervolemic. This review describes the most common sodium-water disorders encountered in pediatric clinics. It emphasizes conditions affecting the brain-kidney axis (syndrome of inappropriate antidiuresis, cerebral salt wasting syndrome, and central and nephrogenic diabetes insipidus). The article proposes diagnostic and therapeutic management based on scientific society publications, case series, and the authors' clinical experience, and summarizes the available knowledge as of 2025 to improve the care of patients with hyponatremia or hypernatremia. A proper understanding of the physiology of sodium homeostasis is crucial for implementing appropriate treatment and reducing the risk of severe complications in young patients in the future.