Hyponatremia

Aka: Hyponatremia, Low Serum Sodium

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II. Definitions

  1. Hyponatremia
    1. Serum Sodium < 135 meq/L
  2. Acute Hyponatremia
    1. Hyponatremia present <48 hours
  3. Chronic Hyponatremia
    1. Hyponatremia present >48 hours (or unknown)

III. Epidemiology

  1. Most common Electrolyte abnormality in U.S. hospitalized patients (affects 15-30% of patients)
  2. Identified in up to 7% of outpatients in U.S.

IV. Pathophysiology

  1. See Sodium and Water Homeostasis
  2. Sodium is the principal osmole of extracellular fluid (which in turn comprises 20% of total body weight)
  3. Hyponatremia is a water excess state
    1. Hypoosmolar Hyponatremia is most common

V. Symptoms: Acute Hyponatremia (develops over <24-48 hours)

  1. Symptom onset when Serum Sodium <125 meq/L
    1. Nausea
    2. Vomiting
    3. Headache
    4. Lethargy
    5. Dizziness
  2. Later or Severe Hyponatremia (Serum Sodium <120 meq/L)
    1. Seizure
    2. Coma
    3. Confusion
    4. Ataxia
    5. Respiratory depression

VI. Symptoms: Chronic Hyponatremia (develops over >48 hours)

  1. Lethargy
  2. Confusion
  3. Muscle cramps
  4. Neurologic Impairment

VII. Causes: Most common

  1. Excessive free water replacement (with or without Sodium losses)
    1. Nausea, Vomiting or Diarrhea
    2. Excessive, prolonged sweating with Exercise
    3. Psychogenic Polydipsia
    4. Hypotonic Saline infusion (e.g. D5 1/2NS)
  2. Excessive Sodium renal excretion (salt wasting)
    1. Diuretics (esp. Thiazide Diuretics, trimethoprim)
    2. Cerebral salt wasting (underlying neurologic disorder)
    3. Low Aldosterone (Mineralcorticoid deficiency)
  3. Syndrome Inappropriate ADH Secretion (SIADH)
    1. Malignancy (e.g. Small Cell Lung Cancer, Pancreatic Cancer)
    2. Lung Infections (e.g. Pneumonia, Empyema, Tuberculosis, Legionella, ARDS)
    3. Neurologic disorders (e.g. Brain Mass, Meningitis, Intracranial Hemorrhage, CVA)
    4. Medications
      1. Amiodarone
      2. Neuropsychiatric agents (e.g. Amitriptyline, Carbamazepine, SSRI, Haloperidol)
      3. Opioids and NSAIDs
  4. Edematous States
    1. Renal Failure or Nephrotic Syndrome
    2. Congestive Heart Failure
    3. Cirrhosis or other severe liver disease

VIII. Labs

  1. Core labs
    1. Comprehensive Metabolic Panel
    2. Serum Osmolality
    3. Urine Sodium
    4. Urine Creatinine
    5. Urine Osmolality
  2. Other labs to consider
    1. Brain Natriuretic Peptide (BNP)
    2. Thyroid Stiumulating Hormone (TSH)

IX. Evaluation: Approach

  1. Is the patient hypervolemic?
    1. See Hypervolemic Hypoosmolar Hyponatremia
    2. Hyponatremia due to Edematous State (Cirrhosis, CHF, Nephrotic Syndrome) or Renal Failure
  2. Measure Serum Osmolarity
    1. Many smaller labs are unable to provide a measured Serum Osmolality
    2. Most cases of Hyponatremia are Hypoosmolar Hyponatremia
      1. Exception: Severe Hyperglycemia (Hyperosmolar Hyponatremia)
        1. Obtain bedside Glucose
      2. Pseudohyponatremia (Normoosmolar Hyponatremia) is rare
  3. Choose an approach (typically Hypoosmolar Hyponatremia, except in severe Hyperglycemia)
    1. Hypoosmolar Hyponatremia (Serum Osms <280)
      1. Most common type of Hyponatremia
      2. Hypovolemic Hypoosmolar Hyponatremia
        1. Fluid losses (e.g. Gastroenteritis)
        2. Third spacing (e.g. Pancreatitis)
        3. Renal Sodium losses
      3. Isovolemic Hypoosmolar Hyponatremia
        1. SIADH
        2. Water Intoxication
        3. Hypothyroidism
        4. Medication Causes of SIADH
      4. Hypervolemic Hypoosmolar Hyponatremia
        1. Edematous State (Cirrhosis, CHF, Nephrotic Syndrome)
        2. Renal Failure
    2. Hyperosmolar Hyponatremia (Serum Osms >300)
      1. Hyperglycemia (typical cause) with water shifting from cells to the extracellular compartment
      2. Serum Sodium falls 1.6 mEq/L per Serum Glucose increase of every 100 mg/dl (over 100 mg/dl)
      3. May also occur with hypertonic infusions (Glucose, Mannitol, Glycine)
    3. Normoosmolar Hyponatremia (Serum Osms 280-300)
      1. Known as Pseudohyponatremia, and occurs in severe Hyperlipidemia or hyperproteinemia
      2. Rare now with newer methadology for Serum Sodium measurement (Sodium electrode)
      3. Consider if known comorbidity
        1. Severe Hypertriglyceridemia (>1500 mg/dl)
        2. Serum Protein >10 g/dl (e.g. Multiple Myeloma)

X. Management

  1. See specific Hyponatremia protocols based on serum osmolarity (esp. Hypoosmolar Hyponatremia)
  2. Do NOT correct Serum Sodium any faster than 6-12 meq/L (mmol/L) per day (most critical single tenet)
  3. See Hyponatremia Management

XI. Prognosis: Mortality

  1. Acute Hyponatremia (Serum Sodium <120 meq/L): 50%
    1. Mortality associated with cerebral edema
  2. Chronic Hyponatremia: 10%
    1. Mortality associated with underlying condition
    2. Also associated with gait instability, falls and Fractures

XII. Prevention

  1. Avoid states of excessive free water intake concurrent with impaired renal water excretion
  2. Avoid Thiazide Diuretics

XIII. References

  1. Le and Drogell (2015) Crit Dec Emerg Med 29(11): 13-19
  2. Kone in Tisher (1993) Nephrology, p. 87-100
  3. Levinsky in Wilson (1991) Harrison's IM, p. 281-84
  4. Rose (1989) Acid-Base and Electrolytes, p. 601-38
  5. Braun (2015) Am Fam Physician 91(5): 299-307 [PubMed]
  6. Miller (2023) Am Fam Physician 108(5): 476-86 [PubMed]

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Ontology: Hyponatremia (C0020625)

Definition (NCI_CTCAE) A disorder characterized by laboratory test results that indicate a low concentration of sodium in the blood.
Definition (NCI) Lower than normal levels of sodium in the circulating blood.
Definition (NCI_NICHD) Hyponatremia is an electrolyte disturbance in which the sodium concentration in the serum is lower than normal. Sodium homeostasis is vital to the normal physiologic function of cells. Hyponatremia is defined as a serum level of less than 135 mEq/L and is considered severe when the serum level is below 125 mEq/L.
Definition (MSH) Deficiency of sodium in the blood; salt depletion. (Dorland, 27th ed)
Definition (PSY) Abnormally low blood sodium level.
Definition (CSP) abnormally low sodium levels in the blood; salt depletion.
Concepts Finding (T033)
MSH D007010
ICD10 E87.1
SnomedCT 190880004, 267507003, 154756008, 312771000009107, 89627008
English Sodium, decreased level, Hyponatremias, HYPONATRAEMIA, LOW SALT SYNDROME, LOW SODIUM SYNDROME, SALT DEFICIENCY, SODIUM BLOOD DECREASED, SODIUM DEPLETION, Hyponatremia, Sodium Serum Decreased, Decreased serum sodium, hyponatremia (diagnosis), hyponatremia, Blood sodium decreased, Sodium blood decreased, Na+ depletion, Sodium depletion, Hyponatraemic syndrome, Low salt syndrome, Syndrome low salt, Low sodium syndrome, Sodium [Na] deficiency, Hyponatremia [Disease/Finding], salt deficiency, depletion sodium, hyponatremia syndrome, decreasing level sodium, decreased serum sodium, deficiency salt, deficiency sodium, deficiencies sodium, sodium depletion, sodium deficiency, HYPONATREMIA, Serum sodium decreased, Serum sodium concentration below normal (finding), Serum sodium concentration below normal, Hyponatremic syndrome, Hyponatraemia, Hyponatremia (disorder), hyponatremic; syndrome, low; salt syndrome, salt; syndrome, low, sodium; depletion, syndrome; hyponatremic, syndrome; salt, low, Hyponatremia, NOS, Hyponatraemia, NOS, hyponatraemia
French HYPONATREMIE, Déplétion de Na+, Syndrome hyposodique, Sodium sérique diminué, Déplétion sodée, Syndrome de carence en sel, DEFICIT EN SEL, DEPERDITION SODIQUE, DIMINUTION DE LA NATREMIE, SYNDROME HYPONATREMIQUE, SYNDROME LIE A DEFICIENCE EN SEL, Sodium sanguin diminué, Syndrome hyponatrémique, Hyponatrémie
Portuguese HIPONATREMIA, Síndrome hiponatrémica, Síndrome hipossalina, Síndrome hiponatrémico, Sódio diminuído no sangue, Depleção de Na+, Sódio sérico diminuído, Depleção de sódio, BAIXA DO SODIO SERICO, DEFICIENCIA EM SAL, DEPLECCAO SODICA, SINDROME DE DEFICIENCIA EM SAL, SINDROME HIPONATREMICO, Natremia diminuída, Síndrome de hiponatremia, Hiponatremia
Spanish HIPONATREMIA, Depleción de Na+, Síndrome de depleción de sal, Síndrome de sodio bajo, Síndromé por déficit de sal, Depleción de sodio, Sodio disminuido sérico, HIPOSALINO, SINDROME, SAL, DEFICIENCIA, SODIO BAJO, SINDROME, SODIO PLASMATICO DISMINUIDO, SODIO, DEPLECION, hiponatremia (trastorno), hiponatremia, Sodio disminuido en sangre, Síndrome hiponatrémico, Hiponatremia
Italian Iponatremia, Sindrome iponatremica, Sindrome da iposodiemia, Sodio sierico diminuito, Sindrome iponatriemica, Deplezione di sodio, Sodio ematico diminuito, Deplezione di Na+, Iponatriemia
Dutch serum natrium verlaagd, natrium bloed verlaagd, syndroom laag sodium, Na+ depletie, natriumdepletie, laag zout syndroom, laag natrium syndroom, hyponatriëmisch; syndroom, laag; zoutsyndroom, natrium; depletie, syndroom; hyponatriëmisch, syndroom; zout, laag, zout; syndroom, laag, bloed natrium verlaagd, hyponatriëmie, hyponatriëmisch syndroom, Hyponatriëmie, Natriëmie, hypo-
German Natrium im Serum erniedrigt, Na+ Depletion, Natrium niedrig Syndrom, Natriumdepletion, Salz niedrig Syndrom, Syndrom, Salz niedrig, NATRIUMABFALL BLUT, NATRIUMMANGELSYNDROM, NATRIUMSPIEGEL ERNIEDRIGT, NATRIUMVERLUST, SALZMANGELSYNDROM, SALZMANGEL, Hyponatriaemie, Hyponatriaemie-Syndrom, Natrium im Blut erniedrigt, Hyponatriämie
Japanese 低ナトリウム症候群, ナトリウム欠乏, 低ナトリウム血症, 低ナトリウム血症候群, Ｎａ＋欠乏, 血清ナトリウム減少, 血中ナトリウム減少, ﾅﾄﾘｳﾑｹﾂﾎﾞｳ, ｹｯﾁｭｳﾅﾄﾘｳﾑｹﾞﾝｼｮｳ, ﾃｲﾅﾄﾘｳﾑｹﾂｼｮｳ, ﾃｲﾅﾄﾘｳﾑｹｯｼｮｳ, ﾃｲﾅﾄﾘｳﾑｹﾂｼｮｳｺｳｸﾞﾝ, ﾃｲﾅﾄﾘｳﾑｼｮｳｺｳｸﾞﾝ, ｹｯｾｲﾅﾄﾘｳﾑｹﾞﾝｼｮｳ
Swedish Hyponatremi
Finnish Hyponatremia
Russian GIPONATRIEMIIA, ГИПОНАТРИЕМИЯ
Czech Snížený sodík v séru, Sodík v krvi snížený, Hyponatremie, Hyponatremický syndrom, Snížený sodík v krvi, Deplece sodíku, hyponatriémie, hyponatrémie, hyponatremie
Polish Hiponatremia, Niedobór sodu
Hungarian Sóhiányos syndroma, Szérum nátrium csökkent, Sóhiányos tünetegyüttes, Nátrium vérszint csökkent, Nátriumhiányos syndroma, Na+ depletio, Hyponatraemiás syndroma, Hyponatraemia, Nátrium depletio
Norwegian Hyponatremi
Derived from the NIH UMLS (Unified Medical Language System)

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