Hyponatremia
Basics
Description
Description
- Sodium <135 mEq/L
- Most common electrolyte disturbance (3–6% of hospitalized patients)
Etiology
PseudohyponatremiaEtiology
- Low measured serum sodium but normal measured serum osmolarity
- Occurs secondary to the displacement of sodium to aqueous phase of serum
- Seen with elevated lipids or proteins
- Lab or blood raw error
- Disease examples include:
- Multiple myeloma
- Hyperlipidemia
Hyponatremia with Normal Osmolarity and Fluid Overload
- Inappropriate retention of water
- Disease examples include:
- CHF
- Cirrhosis
- Renal failure
- Nephrotic syndrome
Hyponatremia with Normal Osmolarity and Euvolemia
- Patients tend to have increased total body water without marked edema
- Purest form of dilutional hyponatremia
- Disease examples include:
- Endocrine abnormalities:
- Hypothyroid
- Stress
- Syndrome of inappropriate antidiuretic hormone (SIADH)
- Diseases that cause SIADH:
- Pulmonary disease (tuberculosis, Legionella, aspergillosis, COPD)
- CNS disorders (malignancy, sarcoid, infection)
- Cancer (small cell lung, pancreas, duodenum)
- HIV infection
- Water intoxication (3–7% of institutionalized psychotic patients), can also occur in marathon runners
- Mineralocorticoid abnormalities
- Postoperative hyponatremia (particularly after transurethral prostatectomy)
- Consumption of large amounts of beer (beer potomania)
- MDMA (Ecstasy)
- Endocrine abnormalities:
Hyponatremia with Normal Osmolarity and Hypovolemia
- Deficits in total body water and total body sodium
- Sodium deficits exceed water deficits
- Possible etiologies include:
- GI losses/colon prep
- Sweating
- Cerebral salt wasting (occurs after head injury or neurosurgical procedures)
- Burns
- Cystic fibrosis
- Salt-wasting nephropathies
- Diuretics
Drug Induced
- Drugs may stimulate antidiuretic hormone (ADH) and cause hyponatremia:
- Amiodarone
- Barbiturates
- Bromocriptine
- Carbamazepine
- Clofibrate
- Cyclophosphamide
- Opiates
- Oxytocin
- Vincristine, vinblastine
- Drugs may increase sensitivity to ADH and cause hyponatremia:
- Chlorpropamide
- NSAIDs
- Drugs may stimulate thirst and cause hyponatremia:
- Amitriptyline
- Ecstasy (MDMA)
- Fluoxetine
- Fluphenazine
- Haloperidol
- Sertraline
- Thiothixene
Hyponatremia with Hyperosmolarity
- Due to excessive osmotically active substances
- Serum osmolarity >295
- Possible etiologies include:
- Elevated glucose (most common cause of hyponatremia)
- Corrected Na+ = 0.016 × (measured glucose – to 100) + measured sodium
- Mannitol infusion
- Maltose and glycine
Pediatric Considerations
- More prone to water intoxication
- High incidence of iatrogenic hyponatremia due to dilute formula or rehydration with water only
- If hyponatremia secondary to DKA, follow hydration per pediatric DKA recommendations
- Age <16 and hypoxia greatest risk for iatrogenic hyponatremia
Pregnancy Considerations
Conivaptan and tolvaptan are class C drugs in pregnancy
Geriatric Considerations
- Tend to develop more symptoms
- Hyponatremia more common due to impaired water secretion and low sodium diets
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Citation
Schaider, Jeffrey J., et al., editors. "Hyponatremia." 5-Minute Emergency Consult, 6th ed., Lippincott Williams & Wilkins, 2020. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307258/all/Hyponatremia.
Hyponatremia. In: Schaider JJJ, Barkin RMR, Hayden SRS, et al, eds. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307258/all/Hyponatremia. Accessed October 9, 2024.
Hyponatremia. (2020). In Schaider, J. J., Barkin, R. M., Hayden, S. R., Wolfe, R. E., Barkin, A. Z., Shayne, P., & Rosen, P. (Eds.), 5-Minute Emergency Consult (6th ed.). Lippincott Williams & Wilkins. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307258/all/Hyponatremia
Hyponatremia [Internet]. In: Schaider JJJ, Barkin RMR, Hayden SRS, Wolfe RER, Barkin AZA, Shayne PP, Rosen PP, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. [cited 2024 October 09]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307258/all/Hyponatremia.
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