Causes of Hyponatremia
Most common cause of hyponatremia in hospitalized patients, often due to excessive water retention.
What is SIADH (Syndrome of Inappropriate Antidiuretic Hormone)?
Low serum osmolality (<275) with urine osmolality >100 in a euvolemic patient suggests this.
What is SIADH?
Most concerning neurologic symptom in acute hyponatremia.
What is seizure?
First-line therapy for symptomatic severe hyponatremia.
What is hypertonic 3% saline?
Hyponatremia in hypothyroidism occurs via this mechanism.
What is reduced free water clearance?
Hyponatremia associated with volume depletion from diarrhea, vomiting, or diuretics.
What is hypovolemic hyponatremia?
Hyponatremia with high urine sodium (>40 mEq/L) in a volume-depleted patient indicates this cause.
What is renal salt wasting (diuretics or adrenal insufficiency)?
A 72-year-old woman presents with mild chronic hyponatremia (Na 127). She has difficulty with balance and recently fell at home. What subtle neurologic effect is most likely?
What is gait instability / increased fall risk?
Maximum safe correction rate of sodium in chronic hyponatremia.
What is <8–10 mEq/L per 24 hours?
Hyponatremia in adrenal insufficiency is primarily due to deficiency of which hormone?
What is cortisol (and sometimes aldosterone)?
Hyponatremia seen in patients with cirrhosis or heart failure due to water retention with edema.
What is hypervolemic hyponatremia?
Hyponatremia in a hyperglycemic patient due to osmotic shift.
What is pseudohyponatremia?
Rapid correction of chronic hyponatremia risks this neurologic condition.
What is Osmotic demyelination syndrome (central pontine myelinolysis)?
Medication class used in SIADH to block ADH-mediated water retention.
What are vaptans (vasopressin receptor antagonists)?
Hyponatremia in hyperglycemia requires sodium correction by how much per 100 mg/dL above normal glucose?
What is +1.6 mEq/L per 100 mg/dL glucose?
This type of hyponatremia occurs in patients receiving excessive hypotonic IV fluids.
What is iatrogenic hyponatremia?
Low urine sodium (<20 mEq/L) in hypovolemic hyponatremia usually indicates this origin.
What is extrarenal sodium loss (vomiting, diarrhea, burns)?
Mild hyponatremia can present with these nonspecific symptoms.
What are fatigue, nausea, headache, confusion?
Chronic asymptomatic hyponatremia in SIADH can be managed with these first steps.
What are fluid restriction and salt tablets?
Electrolyte that should always be corrected along with hyponatremia to prevent ongoing issues.
What is potassium?
Hyponatremia in a psych patient drinking excessive water, often with dilute urine.
What is primary polydipsia?
Hyponatremia with high urine sodium and low serum uric acid in a euvolemic patient points to this diagnosis.
What is SIADH?
A patient with acute hyponatremia (Na 115) develops confusion, vomiting, and a new-onset seizure. On exam, you notice bounding pulses and mild edema. What neurologic complication are these acute symptoms most consistent with?
What is cerebral edema?
This therapy is used when overcorrection of sodium occurs.
What is desmopressin + free water (DDAVP + D5W)?
This lab feature helps distinguish renal vs. extrarenal causes of hypovolemic hyponatremia.
What is urine sodium (<20 = extrarenal, >40 = renal)?