Hypernatraemia is defined as a plasma sodium concentration of >145 mmol/L (145 mEq/L). Hypernatraemia is a state of hyperosmolality, and is primarily a result of water deficit or sodium gain. Due to the maintenance of osmotic equilibrium, intracellular fluid (ICF) becomes volume contracted. The appropriate responses are increased water intake stimulated by thirst, and the excretion of the minimal amount of maximally concentrated urine. Infants and adults with cognitive impairment are most commonly affected because of their inability to express thirst and limited access to water. Hypernatraemia is often the result of several disease processes, and the underlying cause needs to be elicited to correct the sodium balance. The physical consequences of hypernatraemia can be severe, and overlap with many of the precipitating causes.
Hypernatraemia generally occurs in patients at extremes of age, or in those who are physically or cognitively debilitated. An incidence of 1% and a prevalence of 2.5% have been reported for patients admitted to the hospital. Mortality rates range between 45% and 60% for all patients, but may be as high as 80% for older patients.  One study investigating the epidemiology of sodium disturbances in the ICU setting found that both hypernatraemia and hyponatraemia are common in ICU patients, and that they are associated with adverse patient outcomes.  Evidence A Hypernatraemia is diagnosed in males and females in equal numbers.
Associate Professor of Medicine
University of Florida
College of Medicine Jacksonville
GM declares that she has no competing interests.
Consultant and Senior Lecturer in Endocrinology
Royal Victoria Infirmary
RQ declares that he has no competing interests.
Department of Microbiology
Aristotle University of Thessaloniki
DC declares that he has no competing interests.
Associate Professor of Pediatrics
Division of Nephrology
Department of Pediatrics
University of Pittsburgh School of Medicine
Children's Hospital of Pittsburgh
MLM declares that he has no competing interests.
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