Hyponatremia

Key considerations: Severe hyponatremia with seizures or coma, Adrenal crisis (acute adrenal insufficiency), Cerebral salt wasting (post-neurosurgery)

Cannot miss

Severe hyponatremia with seizures or coma
Adrenal crisis (acute adrenal insufficiency)
Cerebral salt wasting (post-neurosurgery)

Likely diagnoses

SIADH
Thiazide diuretics
Heart failure
Cirrhosis
Psychogenic polydipsia
Beer potomania

Red flags

Na <120 mEq/L
Seizures or altered mental status
Acute onset (<48 hours)
Respiratory distress

Workup

history: Duration and acuity of onset; Medications (thiazides, SSRIs, carbamazepine); Fluid intake history; Symptoms: headache, nausea, confusion, seizures; exam: Volume status assessment (hypervolemic, euvolemic, hypovolemic); Neurological exam; Signs of CHF or cirrhosis; labs: Serum Na, osmolality; Urine Na, osmolality; TSH, cortisol; BMP, glucose (corrected Na if hyperglycemic); imaging: CXR if volume overload suspected; CT head if neurological symptoms; bedside: Point-of-care Na (iSTAT); Volume assessment

Management

immediate: Severe symptomatic (seizures/coma): 3% NaCl 100mL IV bolus over 10 min, may repeat x2; Goal: raise Na 4-6 mEq/L in first 6 hours; Do NOT correct >8-10 mEq/L in 24 hours (risk of osmotic demyelination); general: Identify and treat underlying cause; Fluid restriction for SIADH (1-1.5L/day); Monitor Na q4-6h during correction; specific: diagnosis: SIADH; steps: Fluid restriction 1-1.5L/day; Consider salt tabs + furosemide; Tolvaptan (vasopressin antagonist) if refractory — use ONLY in ICU; diagnosis: Hypovolemic; steps: NS resuscitation; Na will auto-correct — monitor to avoid overcorrection; diagnosis: Hypervolemic (CHF/Cirrhosis); steps: Fluid and sodium restriction; Diuretics (loop preferred); Treat underlying cause

Disposition

admit: Na <125 or symptomatic; Active correction needed; Unclear etiology requiring workup; discharge: Mild chronic hyponatremia (Na 130-134) with identified reversible cause; Asymptomatic with outpatient follow-up; consults: Nephrology for severe or refractory hyponatremia; Endocrine if adrenal insufficiency or thyroid disease suspected

Clinical pearls

Overcorrection is dangerous: osmotic demyelination syndrome (ODS) if corrected >10-12 mEq/L in 24 hours
If overcorrecting, give D5W ± desmopressin to slow correction
Corrected Na for hyperglycemia: add 1.6 mEq/L Na for every 100 mg/dL glucose above 100

Source and review

Spasovski et al., Eur J Endocrinol 2014; Verbalis et al., Am J Med 2013. Last reviewed: 2024-11-01