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Emergency And Acute Medicine: Hyponatremia
Basics
Description Hyponatremia is defined as serum sodium <136 meq /> and is the most common electrolyte disturbance, occurring in 1–4% of hospitalized patients.
Etiology
Pseudohyponatremia Low measured sodium with normal serum osmolality due to displacement of sodium in the aqueous phase; seen with hyperlipidemia or hyperproteinemia (e.g., multiple myeloma).
Hyponatremia With Normal Osmolarity And Fluid Overload Inappropriate water retention seen in CHF, cirrhosis, renal failure, and nephrotic syndrome.
Hyponatremia With Normal Osmolarity And Euvolemia Dilutional hyponatremia with increased total body water and minimal edema. Causes include hypothyroidism, stress, SIADH (pulmonary disease, CNS disorders, malignancy, HIV), water intoxication, postoperative states, beer potomania, MDMA use, and mineralocorticoid abnormalities.
Hyponatremia With Normal Osmolarity And Hypovolemia Total body sodium and water loss with sodium loss predominating; causes include GI losses, sweating, burns, cerebral salt wasting, cystic fibrosis, salt-wasting nephropathies, and diuretics.
Drug Induced ADH stimulation (amiodarone, carbamazepine, cyclophosphamide, opiates, vincristine), increased ADH sensitivity (chlorpropamide, NSAIDs), or increased thirst (SSRIs, antipsychotics, MDMA).
Hyponatremia With Hyperosmolarity Due to osmotically active substances, most commonly hyperglycemia. Corrected Na = measured Na + 0.016 × (glucose − 100). Also seen with mannitol, maltose, or glycine.
Pediatric Considerations Higher risk of water intoxication and iatrogenic hyponatremia.
Pregnancy Considerations Vasopressin antagonists are pregnancy class C.
Geriatric Considerations Increased symptom burden due to impaired free water excretion and low sodium intake.
Diagnosis
Signs And Symptoms Mild (Na >120): headache, nausea, vomiting, weakness, anorexia, cramps. Moderate (110–120): confusion, hallucinations, bizarre behavior, incontinence, gait disturbance. Severe (<110): seizures, coma, herniation signs, respiratory arrest. chronic hyponatremia may be asymptomatic.< />pan>
History And Exam Review medications and assess volume status. Perform full neurologic examination.
Essential Workup Confirm serum sodium level with repeat testing.
Diagnosis Tests And Interpretation
Lab Electrolytes, BUN, creatinine, glucose (correct sodium if hyperglycemic), serum and urine osmolality, urine sodium, thyroid and adrenal function, CPK if rhabdomyolysis suspected. Plasma osmolality = 2 × Na + glucose/18 + BUN/2.8.
Imaging CXR for CHF, infection, or malignancy. CT head if altered mental status.
Differential Diagnosis Pseudohyponatremia from hyperglycemia, hyperlipidemia, hyperproteinemia, or radiocontrast exposure.
Treatment
Prehospital Supportive care and IV access.
Initial Stabilization/Therapy ABCs, IV 0.9% NS, naloxone, thiamine, and D50W for altered mental status.
Emergency Department Treatment/Procedures Management depends on severity, chronicity, and cause. Chronic hyponatremia requires slow correction to prevent osmotic demyelination; limit correction to 10-12 mEq/L in 24 hr. Acute severe hyponatremia with seizures requires hypertonic saline to raise sodium 8-10 mEq/L over 4-6 hr or to >120–125 mEq/L, then slow or stop correction. Typical dose is 200–400 mL of 3% saline over 2 hr or 1–2 mL/kg/hr.
Hypovolemic Hyponatremia Restore volume with 0.9% NS.
Euvolemic Or Hypervolemic Hyponatremia Water restriction (<1 l />ay), high salt intake, or 0.9% NS with loop diuretics. Maximum correction rate 0.5 mEq/L/hr.
Medication
First Line 500 mL–1 L isotonic saline bolus.
Adjuncts Furosemide 20–40 mg IV.
Second Line Conivaptan IV or tolvaptan PO for euvolemic or hypervolemic hyponatremia only.
Follow-Up And Disposition
Admission Criteria Symptomatic hyponatremia, sodium <120 meq />, or comorbid risk factors.
Discharge Criteria Sodium >130 mEq/L and asymptomatic, or stable chronic mild hyponatremia with close follow-up.
Follow-Up Recommendations Repeat sodium within one week, especially if diuretic-related.
Pearls And Pitfalls Avoid rapid correction to prevent osmotic demyelination syndrome, especially in women, alcoholics, malnourished patients, those with hypokalemia, or liver transplant history. Perform serial neurologic exams. Beware of falsely low sodium from blood draws near hypotonic IV lines. Thiazide-induced hyponatremia may persist up to two weeks after discontinuation.
Basics
Description Hyponatremia is defined as serum sodium <136 meq /> and is the most common electrolyte disturbance, occurring in 1–4% of hospitalized patients.
Etiology
Pseudohyponatremia Low measured sodium with normal serum osmolality due to displacement of sodium in the aqueous phase; seen with hyperlipidemia or hyperproteinemia (e.g., multiple myeloma).
Hyponatremia With Normal Osmolarity And Fluid Overload Inappropriate water retention seen in CHF, cirrhosis, renal failure, and nephrotic syndrome.
Hyponatremia With Normal Osmolarity And Euvolemia Dilutional hyponatremia with increased total body water and minimal edema. Causes include hypothyroidism, stress, SIADH (pulmonary disease, CNS disorders, malignancy, HIV), water intoxication, postoperative states, beer potomania, MDMA use, and mineralocorticoid abnormalities.
Hyponatremia With Normal Osmolarity And Hypovolemia Total body sodium and water loss with sodium loss predominating; causes include GI losses, sweating, burns, cerebral salt wasting, cystic fibrosis, salt-wasting nephropathies, and diuretics.
Drug Induced ADH stimulation (amiodarone, carbamazepine, cyclophosphamide, opiates, vincristine), increased ADH sensitivity (chlorpropamide, NSAIDs), or increased thirst (SSRIs, antipsychotics, MDMA).
Hyponatremia With Hyperosmolarity Due to osmotically active substances, most commonly hyperglycemia. Corrected Na = measured Na + 0.016 × (glucose − 100). Also seen with mannitol, maltose, or glycine.
Pediatric Considerations Higher risk of water intoxication and iatrogenic hyponatremia.
Pregnancy Considerations Vasopressin antagonists are pregnancy class C.
Geriatric Considerations Increased symptom burden due to impaired free water excretion and low sodium intake.
Diagnosis
Signs And Symptoms Mild (Na >120): headache, nausea, vomiting, weakness, anorexia, cramps. Moderate (110–120): confusion, hallucinations, bizarre behavior, incontinence, gait disturbance. Severe (<110): seizures, coma, herniation signs, respiratory arrest. chronic hyponatremia may be asymptomatic.< />pan>
History And Exam Review medications and assess volume status. Perform full neurologic examination.
Essential Workup Confirm serum sodium level with repeat testing.
Diagnosis Tests And Interpretation
Lab Electrolytes, BUN, creatinine, glucose (correct sodium if hyperglycemic), serum and urine osmolality, urine sodium, thyroid and adrenal function, CPK if rhabdomyolysis suspected. Plasma osmolality = 2 × Na + glucose/18 + BUN/2.8.
Imaging CXR for CHF, infection, or malignancy. CT head if altered mental status.
Differential Diagnosis Pseudohyponatremia from hyperglycemia, hyperlipidemia, hyperproteinemia, or radiocontrast exposure.
Treatment
Prehospital Supportive care and IV access.
Initial Stabilization/Therapy ABCs, IV 0.9% NS, naloxone, thiamine, and D50W for altered mental status.
Emergency Department Treatment/Procedures Management depends on severity, chronicity, and cause. Chronic hyponatremia requires slow correction to prevent osmotic demyelination; limit correction to 10-12 mEq/L in 24 hr. Acute severe hyponatremia with seizures requires hypertonic saline to raise sodium 8-10 mEq/L over 4-6 hr or to >120–125 mEq/L, then slow or stop correction. Typical dose is 200–400 mL of 3% saline over 2 hr or 1–2 mL/kg/hr.
Hypovolemic Hyponatremia Restore volume with 0.9% NS.
Euvolemic Or Hypervolemic Hyponatremia Water restriction (<1 l />ay), high salt intake, or 0.9% NS with loop diuretics. Maximum correction rate 0.5 mEq/L/hr.
Medication
First Line 500 mL–1 L isotonic saline bolus.
Adjuncts Furosemide 20–40 mg IV.
Second Line Conivaptan IV or tolvaptan PO for euvolemic or hypervolemic hyponatremia only.
Follow-Up And Disposition
Admission Criteria Symptomatic hyponatremia, sodium <120 meq />, or comorbid risk factors.
Discharge Criteria Sodium >130 mEq/L and asymptomatic, or stable chronic mild hyponatremia with close follow-up.
Follow-Up Recommendations Repeat sodium within one week, especially if diuretic-related.
Pearls And Pitfalls Avoid rapid correction to prevent osmotic demyelination syndrome, especially in women, alcoholics, malnourished patients, those with hypokalemia, or liver transplant history. Perform serial neurologic exams. Beware of falsely low sodium from blood draws near hypotonic IV lines. Thiazide-induced hyponatremia may persist up to two weeks after discontinuation.
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