Low sodium levels

Disease Description (Causes and Symptoms)

• Definition: A condition in which the serum sodium concentration is less than 135 mmol/L (hyponatremia). Most cases are hypotonic (hypotonic hyponatremia) due to a decrease in plasma osmolality, particularly sodium. Rarely, it may present as hypertonic or isotonic hyponatremia. (Synonym (provided source): hypomagnesemia)
• Pathophysiology: When serum osmolality is low, the osmolality of intracellular fluid becomes relatively higher than that of extracellular fluid, causing water to move into cells. In particular, swelling of brain cells (cerebral edema) causes neurological symptoms. Clinically, the causes and treatment differ according to volume status (hypovolemic, euvolemic, or hypervolemic).
• Major causes: Excessive water intake, sodium loss (such as vomiting, diarrhea, burns, or bleeding), diuretics (especially thiazides), renal failure, diabetes insipidus, congestive heart failure, cirrhosis, hypoparathyroidism and hypothyroidism, medications (such as SSRIs and anticonvulsants), SIADH (syndrome of inappropriate antidiuretic hormone secretion), and others.
• Major symptoms: When mild, asymptomatic or mild nausea, headache, and lethargy. When serum Na decreases rapidly or the condition is severe, confusion, changes in consciousness, vomiting, agitation, seizures (epilepsy), difficulty breathing, and, in severe cases, death.

Treatment Methods and Precautions

• Diagnosis and classification: Identify the cause through serum Na measurement (hyponatremia <135 mmol/L), plasma osmolality (serum osmolality), BUN/creatinine, urine osmolality and urine Na, and assessment of volume status (hypovolemia, euvolemia, or hypervolemia).
• Emergency treatment (severe neurological symptoms, such as decreased consciousness or seizures):
  • Use 3% hypertonic saline, but administer it slowly. The initial goal is to increase the level by small amounts over a short period (e.g., 4–6 mmol/L) until acute neurological symptoms improve.
  • Strictly manage the rate of increase in serum Na: generally, limit the increase within 24 hours to 8 mmol/L or less (6 mmol/L or less in high-risk patients). Overcorrection carries a risk of central pontine myelinolysis.
  • Monitor serum Na every 2–4 hours during treatment and monitor neurological status.
  • If necessary, use desmopressin (DDAVP) to prevent overcorrection.
• Non-emergency, chronic, or mild cases:
  • Treat the cause (discontinue diuretics, treat brain or kidney disease, change medications, etc.).
  • Restrict fluids (e.g., 800–1,200 mL per day, adjusted according to the cause), increase salt intake, or regulate fluid and salt balance.
  • In cases of SIADH: fluid restriction, salt supplementation (tablets of salt or hypertonic solution), and, if necessary, medication treatment (consider use of urine osmotic inhibitors or combination medications).
  • Discontinue or replace medications that cause hyponatremia (thiazide diuretics, some antidepressants and anticonvulsants, etc.).
• Hospitalization and monitoring: Most clinically significant cases of hyponatremia require hospitalization and continuous monitoring (especially during correction).
• Complications and precautions:
  • Risk of central pontine myelinolysis (CPM) due to overly rapid correction (which may cause severe neurological damage or death).
  • In patients with chronic hyponatremia, set the correction target more conservatively.
  • The risk of CPM increases when alcoholism, malnutrition, or toxic or metabolic disorders are present.

Checklist Before an Outpatient Visit (Examples of Items, Tests, and Records to Prepare)

• Bring:
  • A list of all medications currently being taken (including prescription drugs, OTC medications, herbal medicines, and supplements), especially diuretics, SSRIs, anticonvulsants, and antipsychotics
  • Recent test results (serum Na, BUN/Cr, urinalysis, etc.) or medical records
  • The timing and course of symptom onset (whether acute: within 48 hours, or chronic), and major symptoms (vomiting, seizures, changes in consciousness, etc.)
  • Recent changes in weight, average daily fluid intake, and whether vomiting, diarrhea, or excessive sweating has occurred
  • Alcohol consumption history and history of chronic diseases (heart failure, liver disease, kidney disease, etc.)
• Tests that may be requested at the outpatient visit:
  • Blood: Electrolytes (sodium, potassium, and chloride), plasma osmolality, BUN and creatinine, and thyroid and adrenal function tests if necessary
  • Urine: Urine osmolality and urine sodium concentration
  • Electrocardiogram (in cases of severe electrolyte abnormalities), chest X-ray or echocardiography (for assessment of heart failure), etc.

Examples of General Questions to Ask the Doctor

• "What is my current serum sodium level, and is this acute or chronic?"
• "What do you think is the most likely cause of this hyponatremia?"
• "What are the treatment goals (the amount of increase in serum Na), and what is the expected treatment plan?"
• "What are the side effects of this medication (or the medication planned to be prescribed)?"
• "What symptoms during treatment should prompt me to go to the emergency room immediately?"
• "What is the prognosis, and what should I do to prevent recurrence?"

Examples of Disease-Specific Questions

• "Did the symptoms begin suddenly (within 48 hours), or did they progress gradually? (The distinction between acute and chronic affects the treatment goals.)"
• "Among the medications I am currently taking, do I take a thiazide diuretic, SSRI, anticonvulsant, or similar medication? Have I recently started a medication or had a dosage change?"