Rosen & Barkin's 5-Minute Emergency Medicine Consult (692 page)

• Serum sodium <135 mEq/L:
  
  • May be asymptomatic
    
• Serum sodium <130 mEq/L:
  
  • Weakness/lethargy
    
  • Weight gain
    
  • Headache
    
  • Anorexia
    
• Sodium serum <120 mEq/L:
  
  • Altered mental status
    
  • Seizure/coma
    
• Chronic hyponatremia: 50% asymptomatic
  
• High mortality in acute hyponatremia
  

• Thorough medication history
  
• Course of illness (acute, subacute, or chronic)
  

• Volume status
  
• Mental status
  
• Stigmata of malignancy
  

• Diagnosis is 1 of exclusion, need to evaluate for other causes of:
  
  • Depletional or dilutional hyponatremia
    
• Electrolytes, BUN, Cr, glucose, protein, lipids:
  
  • Hyponatremia (serum Na <135 mmol/L)
    
  • Serum hyposmolality (serum Osm <275 mOsm/kg)
    
• Urine osmolality:
  
  • Inability to excrete dilute urine
    
  • Urine osmolality >100 mOsm/kg
    
• Urine sodium:
  
  • Continued urinary excretion of sodium
    
  • Urinary sodium >20 mEq/L
    

• Serum protein levels
  
• Lipid levels
  
• Glucose levels
  
• Serum osmolality
  
• LFT and thyroid function test
  
• Morning cortisol level
  

Consider imaging (CXR, CT head) to screen for pathology causing SIADH (tumors/masses)

• See etiologies above
  
• Increased extracellular fluid (dilutional hyponatremia):
  
  • Renal failure/insufficiency
    
  • CHF
    
  • End-stage liver disease
    
• Normal extracellular fluid (dilutional hyponatremia):
  
  • SIADH
    
  • Myxedema
    
  • Sheehan syndrome (postpartum hypopituitarism)
    
  • Reset osmostat syndromes (dilute urine at lower than normal sodium levels)
    
• Decreased extracellular fluid (depletional hyponatremia):
  
  • Increased losses:
    
    • Excessive sweating (endurance sports)
      
    • GI losses (vomiting, diarrhea)
      
  • 3rd-space sequestration
    
  • Diuretic use
    
  • Aldosterone deficiency:
    
    • Addison disease
      
  • Salt-losing nephropathies:
    
    • Renal tubular acidosis
      
• Pseudohyponatremia (seen in hyperglycemia, hyperproteinemia, hyperlipidemia)
  

TREATMENT

• In patients with altered mental status, maintenance and protection of the airway are paramount.
  
• When hypovolemia is suspected, appropriate fluid resuscitation should be initiated.
  
• Rapid patient evaluation and transport are essential.
  

• Severe symptomatic hyponatremia with CNS manifestations
  
• Endotracheal intubation for patients in need of airway protection
  
• Identify/treat other causes of altered mental status
  
• Treat seizures with benzodiazepines
  
• Proceed to hyponatremia treatment
  

• Most effective treatment of SIADH is successful
  eradication of the underlying cause
  .
  
• Initial treatment of hyponatremia caused by SIADH is the same for all causes of euvolemic/hypervolemic hyponatremia.
  

• Serum sodium usually >125 mEq/L
  
• Fluid restriction 800–1,000 mL/day alone or in conjunction with:
  
  • 0.9% NS infusion and/or IV furosemide
    
• Correct serum sodium by no more than 0.5 mEq/L/hr (5–6 mEq/day):
  
  • Too rapid correction of serum sodium levels can induce
    central pontine myelinolysis
    , associated with development of bulbar palsy, quadriplegia, seizures, coma, and death.
    

• Symptomatic patient, serum sodium <125 mEq/L
  
• Increase serum sodium by no more than 12 mEq/L in 1st 24 hr at a rate of 1 mEq/L/hr (8–12 mEq/day when serum sodium below 125 mEq/L and slow to 5–6 mEq/day when serum sodium rises to 125 mEq/L).
  
• Target level: 125 mEq/L
  
• Treat patients with significant neurologic symptoms with 3% saline solution.
  
• Serum sodium lab testing every 1–2 hr
  

• Serum sodium usually <120 mEq/L
  
• Associated with seizures or coma
  
• Clinical goal: Stop seizure and improve neurologic status
  
• Therapeutic goal: Same as for severe hyponatremia
  
• Administer hypertonic saline solution (3%)
  
• Stop hypertonic saline when symptoms (i.e., seizures) resolve and transition to NS.
  
• IV furosemide to promote diuresis and induce a negative fluid balance.
  
• Once serum sodium = 125 mEq/L, further IV fluid should be in the form of 0.9% saline solution.
  
• Restoration of serum sodium to normal levels should take place over ≥48 hr.
  
• Drugs that inhibit the secretion/effects of ADH:
  
  • Indicated when SIADH not self-limited and cause cannot be removed
    
  • Demeclocycline (blocks effect of ADH)
    

• Conivaptan 20 mg IV over 30 min (for severe hyponatremia in concert with admitting physician)
  
• Demeclocycline: 300 mg PO BID–QID
  
• Hypertonic saline solution (3% NaCl): 250–500 mL (max. initial dose 5 mL/kg):
  
  • 25–100 mL/hr
    
  • Limit rate in rise of serum sodium to 0.5–1 mEq/L/h.
    
  • Discontinue when seizure resolves or serum sodium of 125 mEq/L is reached.
    
  • Rise in serum sodium by 4–6 mEq/L is usually sufficient to stop seizures.
    
• 0.9% NS: Maintenance rates
  
• Lasix: 1 mg/kg up to 20–40 mg IV
  

FOLLOW-UP

• Severe life-threatening hyponatremia
  
• Symptomatic hyponatremia
  
• Serum sodium <125 mEq/L regardless of symptoms
  
• New-onset SIADH in which underlying cause or complications must be diagnosed and treated
  
• Patient’s compliance an issue
  

• Asymptomatic chronic hyponatremia
  
• Serum sodium >125 mEq/L
  
• No unstable comorbid factors
  
• Known diagnosis of SIADH
  

All patients with hyponatremia that meet discharge criteria still require follow-up to check for resolution, monitoring, and/or diagnosis of the underlying cause of the SIADH/hyponatremia.

• SIADH is a diagnosis of exclusion.
  
• Must evaluate for other causes as well as renal, thyroid, adrenal, cardiac, and hepatic dysfunction.
  
• Take a thorough medication history.
  

• Balasubramanian A, Flareau B, Sourberr J. Syndrome of inappropriate antidiuretic hormone secretion.
  Hospital Physician
  . 2007;39:33–36.
  
• Brimioulle S, Orellana-Jimenez C, Aminian A, et al. Hyponatremia in neurological patients: Cerebral salt wasting versus inappropriate antidiuretic hormone secretion.
  Intensive Care Med
  . 2008;34:125–131.
  
• Ellison DH, Berl T. Clinical practice. The syndrome of inappropriate antidiuresis.
  N Engl J Med
  . 2007;356(20):2064–2072.
  
• Gross P. Clinical management of SIADH.
  Ther Adv Endocrinol Metab.
  2012;3(2):61–73.
  
• Verbalis JG. Managing hyponatremia in patients with syndrome of inappropriate antidiuretic hormone secretion.
  J Hosp Med.
  2010;5(suppl 3):S18–S26.
  

See Also (Topic, Algorithm, Electronic Media Element)

Hyponatremia

The author gratefully acknowledges the contribution of Arunachalam Einstein on previous editions of this chapter.

CODES

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

BASICS