Defined as a serum sodium concentration of >145 mmol/L.
Most common presentations are the patient in the ICU who is unable to drink water, has a large urine or stool output, and is unable to concentrate urine normally (usually due to renal failure), and older nursing home residents, usually with dementia.
Underlying aetiology is varied and includes free water losses, inadequate free water intake, or, more rarely, sodium overload.
Examination should focus on volume status, particularly noting severe hypovolaemia, which generally needs urgent correction.
Treatment is directed at addressing the underlying cause, as well as replacing free water deficit and ongoing losses while monitoring serum sodium concentration. It is extremely important not to correct the serum sodium concentration too rapidly.
An electrolyte imbalance consisting of a rise in serum sodium concentration. Hypernatraemia is defined as a serum sodium concentration of >145 mmol/L (normal serum sodium concentration is in the range of 135-145 mmol/L). Severe hypernatraemia has been defined as a serum sodium concentration of >152 mmol/L, or >160 mmol/L in some studies;   however, there is no consensus as to the exact level. Hypernatraemia represents a deficit of water relative to sodium and can result from a number of causes, including free water losses, inadequate free water intake, and, more rarely, sodium overload. Unlike hyponatraemia, hypernatraemia is always associated with serum hyperosmolality.
Clinical Professor of Medicine
San Francisco General Hospital
University of California San Francisco
RS declares that he has no competing interests.
Professor Emeritus of Medicine
Loyola University Chicago
TSI declares that he has no competing interests.
Department of Internal & Emergency Medicine
Hirslanden Klinik Im Park
GL is the author of several references cited in this monograph.
Professor of Pediatrics
University of Pittsburgh Medical School
Children's Hospital of Pittsburgh of UPMC
MLM is the author of a number of references cited in this monograph.
Washington Hospital Center
JHV declares that she has no competing interests.
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