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Hyponatremia in Emergency Medicine

  • Author: Sandy Craig, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
Updated: Jun 20, 2016


Serum sodium concentration and serum osmolarity normally are maintained under precise control by homeostatic mechanisms involving stimulation of thirst, secretion of antidiuretic hormone (ADH), and renal handling of filtered sodium. Clinically significant hyponatremia is relatively uncommon and is nonspecific in its presentation; therefore, the physician must consider the diagnosis in patients presenting with vague constitutional symptoms or with altered level of consciousness. Irreparable harm can befall the patient when abnormal serum sodium levels are corrected too quickly or too slowly. The physician must have a thorough understanding of the pathophysiology of hyponatremia to initiate safe and effective corrective therapy. The patient's fluid status must be accurately assessed upon presentation, as it guides the approach to correction.[1]

Hypovolemic hyponatremia

Total body water (TBW) decreases; total body sodium (Na+) decreases to a greater extent. The extracellular fluid (ECF) volume is decreased.

Euvolemic hyponatremia

TBW increases while total sodium remains normal. The ECF volume is increased minimally to moderately but without the presence of edema.

Hypervolemic hyponatremia

Total body sodium increases, and TBW increases to a greater extent. The ECF is increased markedly, with the presence of edema.

Redistributive hyponatremia

Water shifts from the intracellular to the extracellular compartment, with a resultant dilution of sodium. The TBW and total body sodium are unchanged. This condition occurs with hyperglycemia or administration of mannitol.


The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged. This condition is seen with hypertriglyceridemia and multiple myeloma.



Serum sodium concentration is regulated by stimulation of thirst, secretion of ADH, feedback mechanisms of the renin-angiotensin-aldosterone system, and variations in renal handling of filtered sodium. Increases in serum osmolarity above the normal range (280-300 mOsm/kg) stimulate hypothalamic osmoreceptors, which, in turn, cause an increase in thirst and in circulating levels of ADH. ADH increases free water reabsorption from the urine, yielding urine of low volume and relatively high osmolarity and, as a result, returning serum osmolarity to normal. ADH is also secreted in response to hypovolemia, pain, fear, nausea, and hypoxia.

Aldosterone, synthesized by the adrenal cortex, is regulated primarily by serum potassium but also is released in response to hypovolemia through the renin-angiotensin-aldosterone axis. Aldosterone causes absorption of sodium at the distal renal tubule. Sodium retention obligates free water retention, helping to correct the hypovolemic state. The healthy kidney regulates sodium balance independently of ADH or aldosterone by varying the degree of sodium absorption at the distal tubule. Hypovolemic states, such as hemorrhage or dehydration, prompt increases in sodium absorption in the proximal tubule. Increases in vascular volume suppress tubular sodium reabsorption, resulting in natriuresis and helping to restore normal vascular volume. Generally, disorders of sodium balance can be traced to a disturbance in thirst or water acquisition, ADH, aldosterone, or renal sodium transport.

Hyponatremia is physiologically significant when it indicates a state of extracellular hyposmolarity and a tendency for free water to shift from the vascular space to the intracellular space. Although cellular edema is well tolerated by most tissues, it is not well tolerated within the rigid confines of the bony calvarium. Therefore, clinical manifestations of hyponatremia are related primarily to cerebral edema. The rate of development of hyponatremia plays a critical role in its pathophysiology and subsequent treatment. When serum sodium concentration falls slowly, over a period of several days or weeks, the brain is capable of compensating by extrusion of solutes and fluid to the extracellular space. Compensatory extrusion of solutes reduces the flow of free water into the intracellular space, and symptoms are much milder for a given degree of hyponatremia.

When serum sodium concentration falls rapidly, over a period of 24-48 hours, this compensatory mechanism is overwhelmed and severe cerebral edema may ensue, resulting in brainstem herniation and death.




United States

Hyponatremia is the most common electrolyte disorder, with a marked increase among hospitalized and nursing home patients. A 1985 prospective study of inpatients in a US acute care hospital found an overall incidence of approximately 1% and a prevalence of approximately 2.5%. On the surgical ward, approximately 4.4% of postoperative patients developed hyponatremia within 1 week of surgery. Hyponatremia has also been observed in approximately 30% of patients treated in the intensive care unit.[2]


Though clearly not indicative of the overall prevalence internationally, hyponatremia has been observed in as high as 42.6% of patients in a large acute care hospital in Singapore and in 30% of patients hospitalized in an acute care setting in Rotterdam.[3, 4]


Pathophysiologic differences between patients with acute and chronic hyponatremia engender important differences in their morbidity and mortality.

Patients with acute hyponatremia (developing over 48 h or less) are subject to more severe degrees of cerebral edema for a given serum sodium level. The primary cause of morbidity and death is brainstem herniation and mechanical compression of vital midbrain structures. Rapid identification and correction of serum sodium level is necessary in patients with severe acute hyponatremia to avert brainstem herniation and death.

Patients with chronic hyponatremia (developing over more than 48 h) experience milder degrees of cerebral edema for a given serum sodium level. Brainstem herniation has not been observed in patients with chronic hyponatremia. The principal direct causes of morbidity and death are status epilepticus (when chronic hyponatremia reaches levels of 110 mEq/L or less) and cerebral pontine myelinolysis (an unusual demyelination syndrome that occurs in association with chronic hyponatremia and its rapid correction).

The distinction between acute hyponatremia and chronic hyponatremia has critical implications in terms of morbidity and mortality and in terms of proper corrective therapy.

A 2009 study of 98,411 hospitalized patients found that even mild degrees of hyponatremia were associated with increased in-hospital, 1-year and 5-year mortality rates. Mortality was particularly increased in those with cardiovascular disease, metastatic cancer, and those undergoing orthopedic procedures.[5]

A 2009 study in Copenhagen concluded that hyponatremia in the range of 130-137 mEq/L is also associated with increased mortality rates in the general population.[6]


Overall incidence of hyponatremia is approximately equal in males and females, though postoperative hyponatremia appears to be more common in menstruant females.


Hyponatremia is most common in the extremes of age; these groups are less able to experience and express thirst and less able to regulate fluid intake autonomously. Specific settings that have been known to pose particular risk include the following:

  • Infants fed tap water in an effort to treat symptoms of gastroenteritis
  • Infants fed dilute formula in attempt to ration
  • Elderly patients with diminished sense of thirst, especially when physical infirmity limits independent access to food and drink [7, 8]


Prognosis is dependent on the underlying condition and the severity of disease.

Contributor Information and Disclosures

Sandy Craig, MD Residency Program Director, Carolinas Medical Center; Associate Professor, Department of Emergency Medicine, University of North Carolina at Chapel Hill School of Medicine

Sandy Craig, MD is a member of the following medical societies: Alpha Omega Alpha, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Howard A Bessen, MD Professor of Medicine, Department of Emergency Medicine, University of California, Los Angeles, David Geffen School of Medicine; Program Director, Harbor-UCLA Medical Center

Howard A Bessen, MD is a member of the following medical societies: American College of Emergency Physicians

Disclosure: Nothing to disclose.

Chief Editor

Romesh Khardori, MD, PhD, FACP Professor of Endocrinology, Director of Training Program, Division of Endocrinology, Diabetes and Metabolism, Strelitz Diabetes and Endocrine Disorders Institute, Department of Internal Medicine, Eastern Virginia Medical School

Romesh Khardori, MD, PhD, FACP is a member of the following medical societies: American Association of Clinical Endocrinologists, American College of Physicians, American Diabetes Association, Endocrine Society

Disclosure: Nothing to disclose.

Additional Contributors

Erik D Schraga, MD Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates

Disclosure: Nothing to disclose.

  1. Pfennig CL Md, Slovis CM Md. Sodium Disorders In The Emergency Department: A Review Of Hyponatremia And Hypernatremia. Emerg Med Pract. 2012 Oct. 14(10):1-26. [Medline].

  2. Upadhyay A, Jaber BL, Madias NE. Incidence and prevalence of hyponatremia. Am J Med. 2006 Jul. 119(7 Suppl 1):S30-5. [Medline].

  3. Hawkins RC. Age and gender as risk factors for hyponatremia and hypernatremia. Clin Chim Acta. 2003 Nov. 337(1-2):169-72. [Medline].

  4. Hoorn E, Lindemans J, Zietse R. Hyponatremia in hospitalized patients epidemiology, etiology and symptomatology. J Am Soc Nephrol. 2004. 15:561(A).

  5. Waikar SS, Mount DB, Curhan GC. Mortality after hospitalization with mild, moderate, and severe hyponatremia. Am J Med. 2009 Sep. 122(9):857-65. [Medline].

  6. Sajadieh A, Binici Z, Mouridsen MR, Nielsen OW, Hansen JF, Haugaard SB. Mild hyponatremia carries a poor prognosis in community subjects. Am J Med. 2009 Jul. 122(7):679-86. [Medline].

  7. Turgutalp K, Ozhan O, Gok Oguz E, Horoz M, Camsari A, Yilmaz A, et al. Clinical features, outcome and cost of hyponatremia-associated admission and hospitalization in elderly and very elderly patients: a single-center experience in Turkey. Int Urol Nephrol. 2012 Oct 11. [Medline].

  8. Gosch M, Joosten-Gstrein B, Heppner HJ, Lechleitner M. Hyponatremia in geriatric inhospital patients: effects on results of a comprehensive geriatric assessment. Gerontology. 2012. 58(5):430-40. [Medline].

  9. Cole CD, Gottfried ON, Liu JK, Couldwell WT. Hyponatremia in the neurosurgical patient: diagnosis and management. Neurosurg Focus. 2004 Apr 15. 16(4):E9. [Medline].

  10. Neville KA, Sandeman DJ, Rubinstein A, Henry GM, McGlynn M, Walker JL. Prevention of hyponatremia during maintenance intravenous fluid administration: a prospective randomized study of fluid type versus fluid rate. J Pediatr. 2010 Feb. 156(2):313-9.e1-2. [Medline].

  11. Zeltser I, Pearle MS, Bagley DH. Saline is our friend. Urology. 2009 Jul. 74(1):28-9. [Medline].

  12. Choong K, Kho ME, Menon K, Bohn D. Hypotonic versus isotonic saline in hospitalised children: a systematic review. Arch Dis Child. 2006 Oct. 91(10):828-35. [Medline].

  13. Frizelle FA, Colls BM. Hyponatremia and seizures after bowel preparation: report of three cases. Dis Colon Rectum. 2005 Feb. 48(2):393-6. [Medline].

  14. Li RM, Wang C, Liu ZW, Zhao B. A case of severe hyponatremia induced by duloxetine and ziprasidone. Chin Med J (Engl). 2012 Oct. 125(20):3750-1. [Medline].

  15. Poddighe D. Common finding of mild hyponatremia in children evaluated at the Emergency Department and its correlation with plasma C-reactive protein values. Minerva Pediatr. 2016 Jun. 68 (3):173-6. [Medline].

  16. Brouns SH, Dortmans MK, Jonkers FS, Lambooij SL, Kuijper A, Haak HR. Hyponatraemia in elderly emergency department patients: a marker of frailty. Neth J Med. 2014 Jul. 72 (6):311-7. [Medline].

  17. Fenske W, Störk S, Blechschmidt A, Maier SG, Morgenthaler NG, Allolio B. Copeptin in the differential diagnosis of hyponatremia. J Clin Endocrinol Metab. 2009 Jan. 94(1):123-9. [Medline].

  18. Lindner G, Schwarz C. An update on the current management of hyponatremia. Minerva Med. 2012 Aug. 103(4):279-91. [Medline].

  19. Phillips D. Guidelines released for exercise-associated hyponatremia. Medscape Medical News. WebMD Inc. Available at July 3, 2015;

  20. Hew-Butler T, Rosner MH, Fowkes-Godek S, Dugas JP, Hoffman MD, Lewis DP, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med. 2015 Jul. 25 (4):303-20. [Medline].

  21. Verbalis JG, Goldsmith SR, Greenberg A, Schrier RW, Sterns RH. Hyponatremia treatment guidelines 2007: expert panel recommendations. Am J Med. 2007 Nov. 120(11 Suppl 1):S1-21. [Medline].

  22. Arieff AI. Influence of hypoxia and sex on hyponatremic encephalopathy. Am J Med. 2006 Jul. 119(7 Suppl 1):S59-64. [Medline].

  23. Murase T, Sugimura Y, Takefuji S, et al. Mechanisms and therapy of osmotic demyelination. Am J Med. 2006 Jul. 119(7 Suppl 1):S69-73. [Medline].

  24. Schrier RW, Gross P, Gheorghiade M, Berl T, Verbalis JG, Czerwiec FS, et al. Tolvaptan, a selective oral vasopressin V2-receptor antagonist, for hyponatremia. N Engl J Med. 2006 Nov 16. 355(20):2099-112. [Medline]. [Full Text].

  25. FDA drug safety communication - FDA Limits Duration and Usage Due To Possible Liver Injury Leading to Organ Transplant or Death. Available at Accessed: May 2, 2013.

  26. Olson BR. Vasopressin-receptor antagonists: a new class of agents for the treatment of hyponatremia. Endocr Metab Immune Disord Drug Targets. 2006 Sep. 6(3):249-58. [Medline].

  27. Arieff AI. Hyponatremia, convulsions, respiratory arrest, and permanent brain damage after elective surgery in healthy women. N Engl J Med. 1986 Jun 12. 314(24):1529-35. [Medline].

  28. Ayus JC, Wheeler JM, Arieff AI. Postoperative hyponatremic encephalopathy in menstruant women. Ann Intern Med. 1992 Dec 1. 117(11):891-7. [Medline].

  29. Bachu K, Godkar D, Gasparyan A, et al. Aripiprazole-induced syndrome of inappropriate antidiuretic hormone secretion (SIADH). Am J Ther. 2006 Jul-Aug. 13(4):370-2. [Medline].

  30. Backer HD, Shopes E, Collins SL, Barkan H. Exertional heat illness and hyponatremia in hikers. Am J Emerg Med. 1999 Oct. 17(6):532-9. [Medline].

  31. Berry PL, Belsha CW. Hyponatremia. Pediatr Clin North Am. 1990 Apr. 37(2):351-63. [Medline].

  32. Brown RG. Disorders of water and sodium balance. Postgrad Med. 1993 Mar. 93(4):227-8, 231-4, 239-40 passim. [Medline].

  33. Canuso CM, Goldman MB. Clozapine restores water balance in schizophrenic patients with polydipsia-hyponatremia syndrome. J Neuropsychiatry Clin Neurosci. 1999. 11(1):86-90. [Medline].

  34. Cluitmans FH, Meinders AE. Management of severe hyponatremia: rapid or slow correction?. Am J Med. 1990 Feb. 88(2):161-6. [Medline].

  35. Dehoorne JL, Raes AM, van Laecke E, et al. Desmopressin toxicity due to prolonged half-life in 18 patients with nocturnal enuresis. J Urol. 2006 Aug. 176(2):754-7; discussion 757-8. [Medline].

  36. Egger C, Muehlbacher M, Nickel M, et al. A case of recurrent hyponatremia induced by venlafaxine. J Clin Psychopharmacol. 2006 Aug. 26(4):439. [Medline].

  37. Goldszmidt MA, Iliescu EA. DDAVP to prevent rapid correction in hyponatremia. Clin Nephrol. 2000 Mar. 53(3):226-9. [Medline].

  38. Hettema ME, Halma C. Beer drinker's hyponatraemia: a case report. Neth J Med. 1999 Mar. 54(3):105-7. [Medline].

  39. Holmes SB, Banerjee AK, Alexander WD. Hyponatraemia and seizures after ecstasy use. Postgrad Med J. 1999 Jan. 75(879):32-3. [Medline].

  40. Jacob S, Spinler SA. Hyponatremia associated with selective serotonin-reuptake inhibitors in older adults. Ann Pharmacother. 2006 Sep. 40(9):1618-22. [Medline].

  41. Norman NE, Sneed AM, Brown C, et al. Heparin-induced hyponatremia. Ann Pharmacother. 2004 Mar. 38(3):404-7. [Medline].

  42. O'Connor RE. Exercise-induced hyponatremia: causes, risks, prevention, and management. Cleve Clin J Med. 2006 Sep. 73 Suppl 3:S13-8. [Medline].

  43. Odeh M, Schiff E, Oliven A. Hyponatremia during therapy with amiodarone. Arch Intern Med. 1999 Nov 22. 159(21):2599-600. [Medline].

  44. Oh MS, Carroll HJ. Disorders of sodium metabolism: hypernatremia and hyponatremia. Crit Care Med. 1992 Jan. 20(1):94-103. [Medline].

  45. Oster JR, Singer I. Hyponatremia, hyposmolality, and hypotonicity: tables and fables. Arch Intern Med. 1999 Feb 22. 159(4):333-6. [Medline].

  46. Sirken G, Raja R, Garces J, et al. Contrast-induced translocational hyponatremia and hyperkalemia in advanced kidney disease. Am J Kidney Dis. 2004 Feb. 43(2):e31-5. [Medline].

  47. Soupart A, Ngassa M, Decaux G. Therapeutic relowering of the serum sodium in a patient after excessive correction of hyponatremia. Clin Nephrol. 1999 Jun. 51(6):383-6. [Medline].

  48. Sterns RH. The treatment of hyponatremia: first, do no harm. Am J Med. 1990 Jun. 88(6):557-60. [Medline].

  49. Trimarchi H, Gonzalez J, Olivero J. Hyponatremia-associated rhabdomyolysis. Nephron. 1999. 82(3):274-7. [Medline].

  50. van den Heuvel OA, Bet PM, van Dam EW. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) during treatment with the antipsychotic agents haloperidol and quetiapine [in Dutch]. Ned Tijdschr Geneeskd. 2006 Sep 2. 150(35):1944-8. [Medline].

  51. Watanabe N, Tani M, Tanaka Y, et al. Severe hyponatremia with consciousness disturbance caused by hydroxyurea in a patient with chronic myeloid leukemia [in Japanese]. Rinsho Ketsueki. 2004 Mar. 45(3):243-6. [Medline].

  52. Weisberg LS. Pseudohyponatremia: a reappraisal. Am J Med. 1989 Mar. 86(3):315-8. [Medline].

  53. Wong LL, Verbalis JG. Systemic diseases associated with disorders of water homeostasis. Endocrinol Metab Clin North Am. 2002 Mar. 31(1):121-40. [Medline].

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