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Hyponatremia

Definition
Hyponatremia an electrolyte disorder characterized by low serum sodium concentration, and is typically defined as a serum sodium of < 135 mEq/L.
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Pathophysiology
Causes of hyponatremia include increased water intake (psychogenic polydipsia), low dietary solute intake (tea and toast diet), decreased water excretion secondary to elevated plasma ADH levels (volume depletion, SIADH, severe hypothyroidism, adrenal insufficiency), and expansion of plasma volume in the context of edematous states.
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Epidemiology
The prevalence of hyponatremia in the general population of the US is 1.72%.
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Disease course
Treatment of hyponatremia requires careful attention to avoid overly rapid correction of serum sodium, which can lead to osmotic demyelination syndrome, permanent neurological impairment, and death.
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Prognosis and risk of recurrence
Approximately 40% of patients with osmotic demyelination syndrome recover fully, whereas 25% have persistent neurological deficits. Mortality associated with osmotic demyelination syndrome is approximately 6%.
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Key sources
The following summarized guidelines for the evaluation and management of hyponatremia are prepared by our editorial team based on guidelines from the American Academy of Family Physicians (AAFP 2023), the American Heart Association (AHA/ASA 2023), the Korean Society of Nephrology (KSN/KSEBPR 2022), the American Association for the Study of Liver Diseases (AASLD 2021), the Wilderness Medical Society (WMS 2020), the European Association for the Study of the Liver (EASL 2018; 2010), and the European Society of Intensive Care Medicine (ESICM/ERA-EDTA/ESE 2014).
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Guidelines

1.Classification and risk stratification

Classification: classify hyponatremia based on the documented duration:
Situation
Guidance
Acute
< 48 hours
Chronic
≥ 48 hours
Chronic (presumably)
If it cannot be classified unless there is clinical or anamnestic evidence of the contrary
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  • Severity grading (based on sodium concentration)

  • Severity grading (based on symptoms)

  • Risk of osmotic demyelination

2.Diagnostic investigations

Urine sodium: measure urine sodium concentration on a spot urine sample (obtained and interpreted with concomitant serum sodium concentration) in patients with urine osmolality > 100 mOsm/kg.
B
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  • Urine osmolality

  • Serum osmolality

  • Serum glucose

  • Fractional urinary excretion of uric acid

  • Copeptin-to-urinary sodium ratio

  • Vasopressin levels

3.Medical management

Management of mildly symptomatic patients, acute setting, KSEBPR/KSN: obtain rigorous evaluation for the causes of mild hyponatremia and manage causative diseases to improve clinical outcomes.
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  • Management of mildly symptomatic patients (chronic setting)

  • Management of moderately symptomatic patients

  • Management of severely symptomatic patients (initial management)

  • Management of severely symptomatic patients (adequate response to initial management)

  • Management of severely symptomatic patients (inadequate response to initial management)

  • Management of overly rapid correction

4.Specific circumstances

Patients with hypovolemic hyponatremia: administer IV infusion of a crystalloid solution (0.9% saline or a balanced crystalloid, 0.5-1.0 mL/kg/hour) to restore extracellular volume in patients with hypovolemic hyponatremia.
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  • Patients with hypervolemic hyponatremia

  • Patients with SIADH

  • Patients with exercise-associated hyponatremia (prevention)

  • Patients with exercise-associated hyponatremia (assessment)

  • Patients with exercise-associated hyponatremia (outpatient management)

  • Patients with exercise-associated hyponatremia (inpatient management)

  • Patients with exercise-associated hyponatremia (observation)

  • Patients with HF

  • Patients with liver disease

  • Patients with cerebral disease

5.Preventative measures

Primary prevention in hospitalized patients
Administer isotonic fluids as maintenance fluid therapy to prevent hyponatremia in hospitalized pediatric patients over 1 month and under 18 years of age.
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Insufficient evidence to support administrating isotonic fluids as maintenance fluid therapy to prevent hyponatremia in neonates because of the risk of hypernatremia.
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