Assessment of hypernatraemia

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, rarely, 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.

Epidemiology

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.[1]Hyponatremia and hypernatremia. In: Cislo GS, De Fer TM, eds. General internal medicine consult. The Washington manual series. 2nd ed. St Louis, MO: Lippincott Williams & Wilkins; 2008:158-66.

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.[2]Stelfox HT, Ahmed SB, Khandwala F, et al. The epidemiology of intensive care unit-acquired hyponatremia and hypernatremia in medical-surgical intensive care units. Crit Care. 2008;12:R162. http://ccforum.com/content/12/6/R162 http://www.ncbi.nlm.nih.gov/pubmed/19094227?tool=bestpractice.com

Hypernatraemia is diagnosed in males and females in equal numbers.