| Definitions and general principles |
- Acute hyponatremia is known or (in cases of self-induced water intoxication) can be presumed to have developed over the prior 48 hours. If the duration is unclear, hyponatremia should NOT be considered acute, and this rapid overview should not be applied.
- Severe hyponatremia is defined as a serum concentration <120 mEq/L.
- Moderate hyponatremia is defined as a serum concentration from 120 to 129 mEq/L (ie, <130 mEq/L).
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| Common causes |
- Parenteral fluid administration (eg, post-operative).
- Water intoxication (eg, distance runners; psychotic patients with extreme polydipsia; users of MDMA (ie, 3,4-methylenedioxymethamphetamine or "Ecstasy").
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| Clinical features |
- Unlike with chronic hyponatremia, any symptoms, whether mild or severe, that may be associated with increased intracranial pressure constitute an emergency. Examples include: confusion, gait or movement disturbances, tremor, nausea, vomiting, headache, seizures, obtundation, coma, respiratory arrest.
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| Diagnostic evaluation |
- When possible, focused physical examination should include assessment of respirations, orthostatic blood pressure, pupil size and light reflex, volume status (eg, skin turgor, oral mucosa, edema), and neurologic function (eg, mental status, gait, reflexes, focal deficits).
- Obtain the following laboratory studies: serum creatinine; serum electrolytes (sodium, potassium, bicarbonate); serum glucose; urine sodium, urine potassium, urine osmolality, urine creatinine.
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| Initial management |
- Treat all acutely hyponatremic patients manifesting any symptoms possibly due to increased intracranial pressure (see list above) with a 100 mL bolus of 3% hypertonic saline infused over 10 minutes.
- Treat acutely hyponatremic patients who are not symptomatic with a 50 mL bolus of 3% hypertonic saline infused over 10 minutes unless there is evidence of autocorrection (increasing output of dilute urine and/or evidence that serum sodium concentration is increasing without treatment).
- Goal of therapy is an increase in serum sodium by 4 to 6 mEq/L over a few hours.
- Stop all other intravenous (IV) fluid infusions.
- If the patient is seizing and response to hypertonic saline infusion is delayed, can give a rapid-acting benzodiazepine (eg, lorazepam 4 mg IV).
- If symptoms persist after first bolus, up to two additional 100 mL doses of 3% saline may be given, each infused over 10 minutes (maximum total dose 300 mL).
- Obtain repeat measurements of serum sodium every one to two hours. A rapid, point-of-care sodium analyzer can be used if available. Serum sodium may decline further after presentation in patients with self-induced water intoxication.
- Monitor urine output.
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| Disposition |
- Patients with acute hyponatremia should be hospitalized. Those who manifest or remain at risk for severe complications should be closely monitored in a critical care setting.
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