Defined as a serum sodium concentration of >145 mmol/L.
Most common presentations are the patient in the intensive care unit 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 the older nursing home resident, 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 important not to correct the serum sodium concentration too rapidly in cases of chronic hypernatraemia.
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 variously been defined as a serum sodium concentration of >152 mmol/L, >155 mmol/L, or >160 mmol/L; 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.
History and exam
Key diagnostic factors
- presence of risk factors
- hospital stay
- older age/nursing home resident
- central nervous system manifestations
- diarrhoea or vomiting
- impaired thirst
- weight loss
- orthostatic hypotension
- decreased jugular venous pressure
- other signs of hypovolaemia
- polyuria, polydipsia, increased thirst
Other diagnostic factors
- inability to drink water/limited access to water
- older age
- renal concentrating defect
- gastrointestinal disorders
- insensible water losses
- diabetes insipidus
- use of specific drugs
- large salt intake or administration
- traumatic brain injury
- primary hypodipsia
1st investigations to order
- serum electrolyte panel with glucose, urea, and creatinine
- urine osmolality
- serum osmolality
- urine electrolytes
- urine flow rate
- electrolyte-free water excretion
Investigations to consider
- desmopressin challenge test
- serum arginine vasopressin (AVP) level
- MRI or CT brain
- other tests targeted at evaluating the underlying cause
free water losses
inadequate free water intake
accidental or iatrogenic excess intake of sodium
Use of this content is subject to our disclaimer