Hypernatremia is defined as a serum sodium concentration of >145 mEq/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 etiology 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 hypovolemia, which generally needs urgent correction.
Treatment of hypernatremia 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 hypernatremia.
Hypernatremia is an electrolyte imbalance consisting of a rise in serum sodium concentration; defined as a serum sodium concentration of >145 mEq/L (normal serum sodium concentration is in the range of 135-145 mEq/L). Severe hypernatremia has variously been defined as a serum sodium concentration of >152 mEq/L, >155 mEq/L, or >160 mEq/L. However, there is no consensus as to the exact level.
Hypernatremia 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 hyponatremia, hypernatremia is always associated with serum hyperosmolality.
History and exam
Key diagnostic factors
- hospital stay
- older age/nursing home resident
- central nervous system manifestations
- diarrhea or vomiting
- impaired thirst
- weight loss
- orthostatic hypotension
- decreased jugular venous pressure
- other signs of hypovolemia
- 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, BUN, 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
- Serum creatine phosphokinase (CPK)
- Renal ultrasound
free water losses
inadequate free water intake
accidental or iatrogenic excess intake of sodium
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