Basics
Description
- 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 myeloma
- Hyperlipidemia
Hyponatremia with Normal Osmolarity and Fluid Overload
- Inappropriate retention of water
- Disease examples include:
- CHF
- Cirrhosis
- Renal failure
- Nephrotic 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:
- Hypothyroid
- Stress
- Syndrome 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 infection
- 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)
Hyponatremia with Normal Osmolarity and Hypovolemia
- 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
Drug Induced
- Drugs may stimulate antidiuretic hormone (ADH) and cause hyponatremia:
- Amiodarone
- Barbiturates
- Bromocriptine
- Carbamazepine
- Clofibrate
- Cyclophosphamide
- Opiates
- Oxytocin
- Vincristine, vinblastine
- Drugs may increase sensitivity to ADH and cause hyponatremia:
- Drugs may stimulate thirst and cause hyponatremia:
- Amitriptyline
- Ecstasy
- Fluoxetine
- Fluphenazine
- Haloperidol
- Sertraline
- Thiothixene
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 sodium
- Mannitol infusion
- Maltose 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:
- Headache
- Nausea
- Vomiting
- Weakness
- Anorexia
- Muscle cramps
- Rhabdomyolysis
- 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
- Severe: Na+ <110 mEq/L:
- Signs of herniation
- Decorticate/decerebrate posturing
- Bradycardia
- HTN
- Altered temperature regulation
- Dilated pupils
- Seizure activity
- Respiratory arrest
- Coma/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:
- Hyperglycemia
- Hyperlipidemia
- Hyperproteinemia
- Radiocontrast 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 hr
- OR may dose 1-2 mL/kg/hr of 3% saline solution
- Calculate sodium deficit:
- Na+ deficit = 0.6 (weight in kg) (140 - Na+)
- Sodium contents:
- 1 L 0.9% NS = 154 mEq of sodium
- 1 L 3% saline = 513 mEq of sodium
- Hypovolemic hyponatremia:
- Correct underlying cause
- Replete volume with 0.9% NS IV.
- Primary goals to restore:
- Extracellular fluid
- Cardiac output
- Organ perfusion
- Hypervolemic/euvolemic hyponatremia:
- Water restriction to <1 L/day with high dietary salt intake
- For 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+ deficit
- Replace 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)