Hypernatraemia

Hypernatraemia is 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 of hypernatraemia 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.

Hypernatraemia is an electrolyte imbalance consisting of a rise in serum sodium concentration; defined as a serum sodium concentration of >145 mmol/L (normal serum sodium concentration is in the range of 135-145 mmol/L).[1]Braun MM, Barstow CH, Pyzocha NJ. Diagnosis and management of sodium disorders: hyponatremia and hypernatremia. Am Fam Physician. 2015 Mar 1;91(5):299-307. https://www.aafp.org/afp/2015/0301/p299.html http://www.ncbi.nlm.nih.gov/pubmed/25822386?tool=bestpractice.com ​ Severe hypernatraemia has variously been defined as a serum sodium concentration of >152 mmol/L, >155 mmol/L, or >160 mmol/L.[2]Sam R, Ing TS. Sodium and water disturbances. In: Lai KN, ed. A practical manual of renal medicine, nephrology, dialysis and transplantation. Singapore: World Scientific Publishing C.; 2009:45-79.[3]Nur S, Khan Y, Nur S, et al. Hypernatremia: correction rate and hemodialysis. Case Rep Med. 2014;2014:736073. https://www.hindawi.com/journals/crim/2014/736073 http://www.ncbi.nlm.nih.gov/pubmed/25431600?tool=bestpractice.com [4]Cabassi A, Tedeschi S. Severity of community acquired hypernatremia is an independent predictor of mortality: a matter of water balance and rate of correction. Intern Emerg Med. 2017 Jul 1;12(7):909-11. http://www.ncbi.nlm.nih.gov/pubmed/28669048?tool=bestpractice.com ​​​ 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.