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 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.[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.
http://www.ncbi.nlm.nih.gov/pubmed/25822386?tool=bestpractice.com
Hospital-acquired hypernatraemia is the most common form of hypernatraemia, and it is iatrogenic in some cases.[2]Tsipotis E, Price LL, Jaber BL, et al. Hospital-associated hypernatremia spectrum and clinical outcomes in an unselected cohort. Am J Med. 2018 Jan;131(1):72-82.e1.
http://www.ncbi.nlm.nih.gov/pubmed/28860033?tool=bestpractice.com
[3]Thongprayoon C, Cheungpasitporn W, Yap JQ, et al. Increased mortality risk associated with serum sodium variations and borderline hypo- and hypernatremia in hospitalized adults. Nephrol Dial Transplant. 2020 Oct 1;35(10):1746-52.
https://academic.oup.com/ndt/article/35/10/1746/5521070
http://www.ncbi.nlm.nih.gov/pubmed/31219584?tool=bestpractice.com
[4]Ranjan R, Lo SC, Ly S, et al. Progression to severe hypernatremia in hospitalized general medicine inpatients: an observational study of hospital-acquired hypernatremia. Medicina (Kaunas). 2020 Jul 17;56(7):358.
https://www.mdpi.com/1648-9144/56/7/358
http://www.ncbi.nlm.nih.gov/pubmed/32709029?tool=bestpractice.com
[5]Arzhan S, Roumelioti ME, Litvinovich I, et al. Hypernatremia in hospitalized patients: a large population-based study. Kidney360. 2022 Jul 28;3(7):1144-57.
https://journals.lww.com/kidney360/Fulltext/2022/07000/Hypernatremia_in_Hospitalized_Patients__A_Large.8.aspx
http://www.ncbi.nlm.nih.gov/pubmed/35919520?tool=bestpractice.com
Hypernatraemia that is present on admission to hospital is less common. In one study of 1.9 million patients, 3% had hypernatraemia at admission.[5]Arzhan S, Roumelioti ME, Litvinovich I, et al. Hypernatremia in hospitalized patients: a large population-based study. Kidney360. 2022 Jul 28;3(7):1144-57.
https://journals.lww.com/kidney360/Fulltext/2022/07000/Hypernatremia_in_Hospitalized_Patients__A_Large.8.aspx
http://www.ncbi.nlm.nih.gov/pubmed/35919520?tool=bestpractice.com
In another study, hospital-acquired hypernatraemia developed in 25.9% of hospitalised patients.[2]Tsipotis E, Price LL, Jaber BL, et al. Hospital-associated hypernatremia spectrum and clinical outcomes in an unselected cohort. Am J Med. 2018 Jan;131(1):72-82.e1.
http://www.ncbi.nlm.nih.gov/pubmed/28860033?tool=bestpractice.com
Mortality rates range between 40% and 60% for all patients.[6]Muhsin SA, Mount DB. Diagnosis and treatment of hypernatremia. Best Pract Res Clin Endocrinol Metab. 2016 Mar;30(2):189-203.
https://www.sciencedirect.com/science/article/abs/pii/S1521690X16000415?via%3Dihub
http://www.ncbi.nlm.nih.gov/pubmed/27156758?tool=bestpractice.com
Critically ill patients and older patients with comorbidities have higher mortality rates.[7]Thongprayoon C, Mao MA, Keddis MT, et al. Hypernatremia subgroups among hospitalized patients by machine learning consensus clustering with different patient survival. J Nephrol. 2022 Apr;35(3):921-9.
http://www.ncbi.nlm.nih.gov/pubmed/34623631?tool=bestpractice.com
One review on 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.[8]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.
https://ccforum.biomedcentral.com/articles/10.1186/cc7162
http://www.ncbi.nlm.nih.gov/pubmed/19094227?tool=bestpractice.com
Hospital-acquired hypernatraemia may have a worse prognosis than hypernatraemia present on admission.[2]Tsipotis E, Price LL, Jaber BL, et al. Hospital-associated hypernatremia spectrum and clinical outcomes in an unselected cohort. Am J Med. 2018 Jan;131(1):72-82.e1.
http://www.ncbi.nlm.nih.gov/pubmed/28860033?tool=bestpractice.com
[3]Thongprayoon C, Cheungpasitporn W, Yap JQ, et al. Increased mortality risk associated with serum sodium variations and borderline hypo- and hypernatremia in hospitalized adults. Nephrol Dial Transplant. 2020 Oct 1;35(10):1746-52.
https://academic.oup.com/ndt/article/35/10/1746/5521070
http://www.ncbi.nlm.nih.gov/pubmed/31219584?tool=bestpractice.com
[4]Ranjan R, Lo SC, Ly S, et al. Progression to severe hypernatremia in hospitalized general medicine inpatients: an observational study of hospital-acquired hypernatremia. Medicina (Kaunas). 2020 Jul 17;56(7):358.
https://www.mdpi.com/1648-9144/56/7/358
http://www.ncbi.nlm.nih.gov/pubmed/32709029?tool=bestpractice.com
Hypernatraemia is diagnosed in males and females in equal numbers.
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