Hypernatremia is common in patients with severe COVID-19 and indicates a poor prognosis

Background: Fluid homeostasis, including electrolyte balance, is dependent on an interaction between the renin-angiotensin-aldosterone system (RAAS) and the release of arginine vasopressin from the pituitary. An imbalance can lead to both hypo- and hypernatremia. We investigated the frequency, dynamics and severity of electrolyte imbalance in critically ill patients with COVID-19. Methods: In this retrospective cohort study 223 patients with confirmed COVID-19, treated at the intensive care unit (ICU), were included. Levels of electrolytes, base excess, pH and serum osmolality were collected from the laboratory database. Clinical data was retrieved from patients’ medical records. Results: Hyponatremia was present in 63% of the patients, at admission. Within two weeks of hospitalization, 65% of the patients developed hypernatremia often combined with a rise of base excess. The mortality rate was twice as high in the group with hypernatremia compared to the patients not developing hypernatremia. Treatment of hypertension before the onset of COVID-19 was more common in patients without hypernatremia. Conclusion: Our study shows that hypernatremia is very common in severe COVID-19. Patients that developed hypernatremia needed longer time in ICU and had a higher risk of dying, suggesting that the level of sodium is an important indicator of severity in COVID-19.