Hyponatremia is considered when the serum sodium is <135 mmol/L. It is frequently encountered in patients presenting to the emergency department. The symptoms of hyponatremia are often unspecific and include a recent history of falls, weakness, and vertigo. It may be caused by diuretics, heart failure, as well as Syndrome of Inappropriate Antidiuresis (SIAD), and its diagnosis can be challenging. Emergency treatment of hyponatremia should consider the presence of symptoms and focus on distinguishing between acute and chronic hyponatremia.

The following points are crucial in managing hyponatremia in the emergency department-

• It is reasonable to suspect hyponatremia if the patient is taking diuretics, especially thiazide (−like) and aldosterone-antagonists, have a history of heart failure or cirrhosis of the liver, malignancy, Pulmonary diseases, or psychiatric conditions.
• Hyponatremia is often associated with symptoms like Falls, Weakness, Vertigo, Seizures, Neurocognitive deficits (disorientation, somnolence), Nausea, and vomiting.
• The diagnostic workup should include the following-

o    Serum: osmolality, potassium, glucose, creatinine, urea, TSH

o    Urine: osmolality, sodium

o    a critical review of medications with special consideration of Diuretics and Psychotropic drugs

• Acute therapy should be initiated in-

o    Patients with moderate to severe symptoms attributable to hyponatremia

o    150 ml of 3% NaCl i.v. over 20 min

o    Check serum sodium after 20 min

o    Repeat 3% NaCl if the patient is still symptomatic and increase in serum sodium <5 mmol/L

o    Patients with a documented acute fall in serum sodium >10 mmol/L

o  150 ml of 3% NaCl i.v. over 20 min

o   Check serum sodium after 20 min

• Other therapeutic measures include withholding provoking medications whenever possible (e.g., thiazide diuretics), starting i.v. hydration in case of hypovolemia and performing frequent measurements of serum sodium.
• Rule out Hyperglycemia-induced hyponatremia as: [Na+] declines by 1.6 mmol/L forever 100 mg/dL increase in blood glucose
• It is crucial to rule out pseudo hyponatremia by determining sodium by an ion-sensitive electrode (blood gas analyzer) – common in extreme forms of hyperproteinemia or hyperlipidemia.
• Observe large volumes of i.v. fluids unless the patient is obviously hypovolemic in order to avoid furth.er serum sodium decline in case of SIAD(H)
• Admit Severe and/or symptomatic hyponatremia patients to a unit with frequent sodium and clinical checks (e.g., intermediate care).
• Treat Asymptomatic patients with mild hyponatremia in otherwise stable conditions as outpatients with ambulatory care and perform further workup.

Lindner G, Schwarz C, Haidinger M, Ravioli S. Hyponatremia in the emergency department. The American Journal of Emergency Medicine. 2022;60: 1-8. https://doi.org/10.1016/j.ajem.2022.07.023.