Neonatal Hypernatremia By Kevin C Dysart, MD, Nemours / Alfred I duPont Hospital for Children Reviewed / Revised Mar 2021 | Modified Sep 2022 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Prevention Key Points Topic Resources Maintenance Fluid Calculation... Hypernatremia is a serum sodium concentration > 150 mEq / L (> 150 mmol / L), usually caused by dehydration.