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Hyponatremia, Emergency Medicine

Basics

Description

- 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

- 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)

- 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)

- Deficits in total body water and total body sodium - Sodium deficits exceed water deficits - Possible etiologies include: - GI losses - Sweating - Cerebral salt wasting (occurs after head injury or neurosurgical procedures) - Burns - Cystic fibrosis - Salt-wasting nephropathies - Diuretics

- Due to excessive osmotically active substances - 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

- Moderate: Na+ between 110 and 120 mEq/L: - Impaired response to verbal stimuli - Decreased response to painful stimuli - Visual/auditory hallucinations - Bizarre behavior - Incontinence - Hyperventilation - Gait disturbance

- Pseudohyponatremia due to: - Hyperglycemia - Hyperlipidemia - Hyperproteinemia - Radiocontrast dye particularly in chronic renal insufficient patients

- Hypovolemic hyponatremia: - Correct underlying cause - Replete volume with 0.9% NS IV. - Primary goals to restore: - Extracellular fluid - Cardiac output - Organ perfusion

  • Sodium <136 mEq/L
  • Most common electrolyte disturbance (1-4% of hospitalized patients)

Etiology

Pseudohyponatremia

  • 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 myelomaHyperlipidemia

Hyponatremia with Normal Osmolarity and Fluid Overload

  • Inappropriate retention of water
  • Disease examples include:CHFCirrhosisRenal failureNephrotic 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:HypothyroidStressSyndrome 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 infectionWater intoxication (3-7% of institutionalized psychotic patients), can also occur in marathon runnersMineralocorticoid abnormalitiesPostoperative hyponatremia (particularly after transurethral prostatectomy)Consumption of large amounts of beer (beer potomania)MDMA (Ecstasy)

Hyponatremia with Normal Osmolarity and Hypovolemia

  • Deficits in total body water and total body sodium
  • Sodium deficits exceed water deficits
  • Possible etiologies include:GI lossesSweatingCerebral salt wasting (occurs after head injury or neurosurgical procedures)BurnsCystic fibrosisSalt-wasting nephropathiesDiuretics

Drug Induced

  • Drugs may stimulate antidiuretic hormone (ADH) and cause hyponatremia:AmiodaroneBarbituratesBromocriptineCarbamazepineClofibrateCyclophosphamideOpiatesOxytocinVincristine, vinblastine
  • Drugs may increase sensitivity to ADH and cause hyponatremia:
  • Drugs may stimulate thirst and cause hyponatremia:AmitriptylineEcstasyFluoxetineFluphenazineHaloperidolSertralineThiothixene

Hyponatremia with Hyperosmolarity

  • Due to excessive osmotically active substances
  • Possible etiologies include:Elevated glucose (most common cause of hyponatremia)Corrected Na+ = 0.016 — (measured glucose - to 100) + measured sodiumMannitol infusionMaltose and glycine
  • 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

Conivaptan and Tolvaptan are class C drugs in pregnancy.

  • Tend to develop more symptoms
  • Hyponatremia more common due to impaired water secretion and low sodium diets

Diagnosis

Signs and Symptoms

  • Mild: Na+ >120 mEq/L:HeadacheNauseaVomitingWeaknessAnorexiaMuscle crampsRhabdomyolysis
  • Moderate: Na+ between 110 and 120 mEq/L:Impaired response to verbal stimuliDecreased response to painful stimuliVisual/auditory hallucinationsBizarre behaviorIncontinenceHyperventilationGait disturbance
  • Severe: Na+ <110 mEq/L:Signs of herniationDecorticate/decerebrate posturingBradycardiaHTNAltered temperature regulationDilated pupilsSeizure activityRespiratory arrestComa/unresponsive

Chronic

May be asymptomatic

History

Review patient medication list.

Physical Exam

  • Assess volume status including skin turgor, neck veins, peripheral edema, and signs of ascites
  • Perform a complete neurologic exam.

Essential Workup

Serum sodium level:

  • Recheck sodium to verify.

Diagnosis Tests & Interpretation

Lab

  • Electrolytes, BUN/creatinine
  • Glucose:Correct sodium value accordingly if severe hyperglycemia (add 1.6 Na for each 100 mg/dL of glucose above normal)
  • Calculate osmolality:Plasma osmolality = [2 — NA (mEq L) + Glucose/18 + BUN/2.8]
  • Urine sodium
  • Serum and urine osmolality
  • Thyroid function test
  • Adrenal function tests
  • CPK for possible rhabdomyolysis

Imaging

  • CXR to rule out CHF, infection, and tumor
  • CT of head, particularly if patient has AMS

Differential Diagnosis

  • Pseudohyponatremia due to:HyperglycemiaHyperlipidemiaHyperproteinemiaRadiocontrast dye particularly in chronic renal insufficient patients

Treatment

Pre-Hospital

  • Establish IV
  • Supportive care

Initial Stabilization/Therapy

  • ABCs
  • Initiate IV fluid with 0.9% NS.
  • Naloxone, thiamine, D50W (or Accu-Chek) for altered mental status

Ed Treatment/Procedures

  • Depends on severity and chronicity of hyponatremia and underlying etiology
  • Chronic hyponatremia is to be corrected slowly to minimize osmotic demyelination syndrome. Correction should be limited to 10-12 mmol/L in 24 hr
  • Acute hyponatremia with severe CNS symptoms/actively seizing:Goal:Raise serum sodium by 8-10mEq/L in 4-6 hr or to level >120-125 mEq/L with administration of hypertonic saline, slow or discontinue when seizure subsides.200-400 mL of 3% saline solution will be the approximate amount needed in most adults over the 1st 2 hrOR may dose 1-2 mL/kg/hr of 3% saline solutionCalculate sodium deficit:Na+ deficit = 0.6 (weight in kg) (140 - Na+)Sodium contents:1 L 0.9% NS = 154 mEq of sodium1 L 3% saline = 513 mEq of sodium
  • Hypovolemic hyponatremia:Correct underlying causeReplete volume with 0.9% NS IV.Primary goals to restore:Extracellular fluidCardiac outputOrgan perfusion
  • Hypervolemic/euvolemic hyponatremia:Water restriction to <1 L/day with high dietary salt intakeFor faster correction of sodium:Administer IV 0.9% NS with loop diuretic (furosemide).Maximum rate of correction = 0.5 mEq/L/hr

Medication

  • Furosemide: 20-40 mg IV push
  • Sodium replacement:Calculate Na+ deficitReplace no more than 1/2 of requirement over 8-12 hr

First Line

500 mL-1 L of saline for a fluid challenge

Second Line

  • Conivaptan: Argininevasopressin antagonist
  • 20 mg IV loading dose over 30 min followed by 20 mg continuous IV infusion over 24 hr
  • Tolvaptan: Selective vasopressin V2 receptor antagonist dose 15 mg/d PO and may increase in 24 hr to 30 mg
  • Conivaptan and tolvaptan are for the treatment of euvolemic and hypervolemic hyponatremia only

Follow-Up

Disposition

Admission Criteria

  • Symptomatic hyponatremia
  • Sodium <120 mEq/L
  • Asymptomatic, mild hyponatremia (Na+ 120-127 mEq/L), with comorbid factors

Discharge Criteria

  • Sodium >130 mEq/L and asymptomatic
  • Known chronic history of hyponatremia with no acute changes
  • Asymptomatic, mild hyponatremia (Na+ 120-129 mEq/L) with no comorbid factors; however, must have close outpatient follow-up.

Followup Recommendations

Have repeat serum sodium within a week, particularly if related to thiazide diuretics

Pearls and Pitfalls

  • Too rapid correction may cause osmotic demyelination syndrome
  • Females, alcoholics, malnourished patients, hypokalemia, and history of liver transplant are risk factors for osmotic demyelination syndrome.
  • Repeat and document neurologic exam during correction.
  • Beware of falsely low sodium when blood is drawn near an IV site with hypotonic fluid.
  • Thiazide diuretics may cause persistent hyponatremia up to 2 wk after discontinuation.

Additional Reading

  • Lien YH, Shapiro JI. Hyponatremia: Clinical diagnosis and management. Am J Med. 2007;120(8):653-658.
  • Lin M, Liu SJ, Lim IT. Disorders of water imbalance. Emerg Med Clin North Am. 2005;23(3):749-770, ix.
  • Palmer BF, Gates JR, Lader M. Causes and management of hyponatremia. Ann Phamacother. 2003;37:1694-1702.
  • Pfennig CL, Slovis CM. Sodium disorders in the emergency department: A review of hyponatremia and hypernatremia. Emerg Med Pract. 2012;14(10):1-26.
  • Verbalis JG, Goldsmith SR, Greenberg A, et al. Hyponatremia guidelines 2007: Expert panel recommendations. Am J Med. 2007;120(11):S1-S21.

See Also (Topic, Algorithm, Electronic Media Element)

Hypernatremia

Codes

ICD9

  • 253.6 Other disorders of neurohypophysis
  • 276.1 Hyposmolality and/or hyponatremia
  • 276.69 Other fluid overload

ICD10

  • E22.2 Syndrome of inappropriate secretion of antidiuretic hormone
  • E87.1 Hypo-osmolality and hyponatremia
  • E87.79 Other fluid overload

SNOMED

  • 89627008 Hyponatremia (disorder)
  • 55004003 Syndrome of inappropriate vasopressin secretion (disorder)
  • 71785001 Water intoxication syndrome (disorder)
  • 237843009 Pseudohyponatremia
  • 237844003 Drug-induced hyponatremia (disorder)
  • 307201006 Dilutional hyponatremia (disorder)
  • 74003001 Hyponatremia with normal extracellular fluid volume (disorder)